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Natural Medicines Used for Improving Athletic Performance
Stimulants | Steroids & Hormones | Steroid Enhancers & Precursors
Adaptogens | Amino Acids | Antioxidants
Endurance/Muscle/Metabolism/Energy Enhancers | The Bottom Line | References
 

The use of performance enhancing drugs and supplements, known as "ergogenic aids," is very popular among many trained athletes. As many as 76% of college athletes and up to 100% of athletes in some sports, such as weight lifting, take a supplement.16271 Many of these products are also used by the health conscious mainstream population. Worldwide spending on sports-oriented foods, beverages, and supplements reached $5.4 billion in 2005 and continues to grow rapidly.16272

These products are used for a variety for purposes ranging from building muscle and improving endurance to helping with exercise recovery.

Commonly Used Conventional and Natural Medicines for Improving Athletic Performance*
Adaptogens
Amino Acids
Antioxidants
Endurance/Muscle/Metabolism/Energy Enhancers
Steroids & Hormones
  • Anabolic steroids
  • Human Growth Hormone
Steroid Enhancers & Precursors
Stimulants
*Note: Many natural products are tried for improving athletic performance, but very few have reliable evidence that they work. Inclusion in this list does NOT imply that these products are effective for improving athletic performance.

 
 
 
Stimulantsreturn to top 

Stimulant drugs are among the best known athletic performance enhancers. These include amphetamines, pseudoephedrine, caffeine, cocaine, and others. These drugs release catecholamines such as norepinephrine and are thought to increase alertness and decrease feelings of fatigue.16273

Most of these drugs have not been consistently shown to improve athletic performance. However, caffeine does seem to have some effects on performance. It is probably the most commonly used stimulant among athletes. Several small clinical studies show that taking caffeine 2-10 mg/kg can increase endurance and increase time to exhaustion.10203,11832

Caffeine is usually well-tolerated when taken in moderate doses. But higher doses, those over 250-300 mg/day, can cause significant side effects including insomnia, nervousness, GI upset, tachycardia, tremors, diuresis, chest pain, arrhythmias, and others.

Caffeine is found in many energy drinks...Enviga, Jolt, Red Bull, Monster, NOS, Rockstar, and many others. These can contain from 50-350 mg caffeine per serving.

Some people take caffeine in a concentrated pill form or in a dietary supplement containing caffeine. Several natural medicines found in supplements are sources of a significant amount of caffeine. These include guarana, green tea extract, mate, cola nut, and others.

Practice Pearl
Advise patients about the many different sources of caffeine. People who consume energy drinks might end up getting too much caffeine if they also take a supplement containing a hidden source of caffeine. This is especially important for athletes. The National Collegiate Athletic Association (NCAA) allows caffeine within limits. Urine concentrations over 15 mcg/mL are prohibited. Explain to athletes that it takes about 8 cups of coffee providing 100 mg/cup to achieve this urine concentration for most people.16273

Other natural stimulants are also used, often in combination with caffeine.

Ephedra was once widely used in combination with caffeine for both weight loss and to enhance athletic performance. Ephedra is a plant source of several stimulant drugs including ephedrine, phenylpropanolamine, and pseudoephedrine. A combination of the stimulants found in ephedra plus caffeine seems to improve endurance; however, this may be due primarily to the caffeine content alone because the stimulant drugs alone do not appear to have this effect.16271

Ephedra also appears to be unsafe and was banned in North America in 2004. This was due to over 140 reports of serious adverse events including myocardial infarction, stroke, seizure, and death.1381,5047,6486 Despite these risks, ephedra is still available for purchase in other countries and through internet retailers. Advise patients not to use products containing ephedra.

Bitter orange has now largely replaced ephedra in energy/stimulant formulations. In fact, most "ephedra free" products actually contain bitter orange, which is just a stimulant by a different name.

Bitter orange contains the stimulant synephrine, which is an isomer of phenylephrine. Like ephedra, there is no reliable evidence that bitter orange alone improves athletic performance. There is also growing concern about the safety of bitter orange. Several case reports are now emerging linking bitter orange to stroke, myocardial infarction, arrhythmia, and death.2040,6979,12030,13039,13067,14326,14342 Advise patients not to use bitter orange-containing products.

Practice Pearl
Help patients identify bitter orange-containing products. Bitter orange goes by many names and might appear on supplement labels as Aurantium, Aurantii Fructus, Citrus aurantium, Fructus Aurantii, Orange Peel Extract, Zhi Shi, or others.

 
View brands containing:
-Caffeine
  Question #1
Which of the following stimulants has been shown to improve athletic performance?
  • View brands containing:
    -Guarana
    -Green tea extract
    -Mate
    -Cola nut
      Question #2
    TRUE or FALSE. Consuming 2 servings of Rockstar energy drink, providing 80 mg caffeine per serving, might increase urine caffeine concentrations over the permissible limit of 15 mcg/mL.
  • View brands containing:
    -Ephedra
    -Bitter orange
      Question #3
    Ephedra was removed from the market in North America because:
  • Steroids & Hormonesreturn to top 

    Anabolic steroids such as testosterone have a long history of use for improving physical performance. Testosterone was first synthesized in 1935 and was used by German soldiers in World War II to increase aggressiveness. It was also used by Russian athletes during the 1956 World Games. Since then several new testosterone-derived "designer" steroids have been developed and have had widespread use in sports. Anabolic steroids were not banned from the Olympics until 1976.16273

    In addition to steroids, other hormones are also used, especially human growth hormone. Human growth hormone is popular among athletes, despite the fact that there is no evidence to support its use. Human growth hormone can improve strength in people who are deficient, but has no effect on strength in healthy young people.16271,16273

    Human growth hormone is banned by both the National Collegiate Athletic Association (NCAA) and the International Olympic Committee (IOC), but there is no reliable test to detect its use.16273

    		 
      Question #4
    Which of the following is TRUE about bitter orange?
  • Steroid Enhancers & Precursorsreturn to top 

    Several "natural" products are also used as steroid or hormone precursors or enhancers.

    Dehydroepiandrosterone (DHEA) is normally secreted by the adrenal glands and testes. In the body, DHEA is converted to androstenedione and androstenediol, which are the immediate precursors to androgens (testosterone) and estrogens (estrone).3232,6098

    Despite the metabolic connection to testosterone, DHEA does not increase testosterone levels in men and there is no reliable evidence that it improves athletic performance.6010,6011,9694,11465 Some clinical research shows that it does NOT improve strength or muscle mass in elderly patients.10406

    Androstenedione does appear to modestly increase testosterone levels, short-term. But when used for longer than a month testosterone levels return to normal.1365,1905,6000,7236,7514,10696 Clinical research also shows that androstenedione does NOT improve muscle strength, muscle mass, or lean body mass when used for 2-3 months in weight trainers.1365,1905,6000,7514

    Androstenediol acts similar to androstenedione. Clinical research also shows that androstenediol does NOT improve muscle strength or muscle mass after 3 months in resistance trainers.1905

    There are concerns about the safety of taking DHEA, androstenedione, and androstenediol supplements. Taking supraphysiological amounts of these alters the normal hormonal balance in both men and women. In men, these supplements actually increase estrogen above normal levels. In women they increase testosterone. As a result, men might experience gynecomastia, testicular atrophy, and other estrogen-related side effects. Women might experience androgen-related side effects such as hirsutism, acne, deepening of the voice, and many others.

    Several other natural medicines are used because they are thought to stimulate production of endogenous hormones.

    Chrysin is a naturally occurring plant flavonoid that can be isolated from passionflower, silver linden, and some geranium species. Chrysin has aromatase inhibitor activity in vitro. Therefore, it's thought that chrysin can prevent the aromatization of androstenedione and testosterone to estrogen.7506

    Chrysin is often combined with androstenedione and other testosterone precursors to prevent their conversion to estrogen, resulting in decreased estrogen-related side effects and increased testosterone levels. But research in humans shows that chrysin does not do this. Combining chrysin with androstenedione and DHEA does NOT significantly decrease estrogen levels, increase testosterone levels, or improve strength or body composition in response to resistance training.7514

    Gamma hydroxybutyrate (GHB) is commonly known as a "date-rape" drug. As a result it became a schedule I controlled substance in 2000. Nonetheless, it is still available from retailers on the internet. There is interest from athletes in the use of GHB for improving performance because it stimulates the release of growth hormone.5804 However, as with growth hormone itself, there is no reliable evidence that taking GHB improves athletic performance.

    There are also significant concerns about safety. GHB has been linked to several serious side effects including hallucinations, drowsiness, nausea, vomiting, depressed respiration, eosinophilia-myalgia syndrome, and many others.

    Extracts of Avena sativa or "oats" are also promoted as improving both athletic and sexual performance. Promoters suggest that these extracts increase steroid production or free up bound testosterone to increase its effects in the body. There is no reliable evidence to support these claims.

    Puncture vine is often included in natural product formulations promoted for improving athletic performance. Research in animal models suggests that the puncture vine constituent, protodioscin, stimulates increased levels of testosterone, DHEA, and other hormones.12675,12677 However, research in humans shows that taking puncture vine in combination with androstenedione, DHEA, and other supplements increases androstenedione levels, but not levels of other hormones.13255 Additionally, clinical research shows that taking puncture vine alone, or in combination with androstenedione, DHEA, and other supplements, does NOT significantly improve body composition or performance.7514,13255

    		 
      Question #5
    TRUE or FALSE. Human growth hormone improves strength in healthy young adults.
  • View brands containing:
    -DHEA
    -Androstenedione
    -Androstenediol
      Question #6
    Which of the following side effects might be expected in a male who takes large doses of androstenedione?
  • View brands containing:
    -Chrysin
    -GHB
      Question #7
    Several natural products are promoted as testosterone precursors or enhancers. Which of the following has been shown to INCREASE testosterone levels in males?
  • View brands containing:
    -Oats
    -Puncture vine
    Adaptogensreturn to top 

    The term "adaptogen" refers to products that are thought to improve the body's ability to combat stress, fatigue, and trauma. Many natural products classified as adaptogens are used by athletes to improve endurance and performance.

    Both American ginseng and Panax ginseng (aka, Asian ginseng) contain ginsenosides and polysaccharides, which are thought to have a variety of effects on hormones such as estrogen, blood glucose, immunomodulation, and acetylcholine.6461,9736,10984,11351

    How exactly ginseng might affect athletic performance is not clear. In fact, preliminary clinical research shows that taking American ginseng 1600 mg for 4 weeks does not significantly improve measures of athletic performance. However, there is speculation that it might help reduce muscle damage during aerobic exercise.14804

    Similarly, several clinical studies show that taking Panax ginseng does not significantly improve measures of aerobic exercise performance.1427,4230,4231,4236

    Siberian ginseng is another commonly used adaptogen. Despite its name, Siberian ginseng is a completely different herb than American ginseng and Panax ginseng. It is said that the Soviet Union wanted to provide its athletes with the advantage they thought was offered by Panax ginseng, but wanted a less expensive version; therefore, Siberian ginseng was used in its place. This is why most studies on Siberian ginseng have been done in Russia.797

    As with American ginseng and Panax ginseng, Siberian ginseng has been shown to be ineffective for improving measures of athletic performance.2335,7522,7593,7600,7601,8994

    		 
    View brands containing:
    -American ginseng
    -Panax ginseng
    View brands containing:
    -Siberian ginseng
    Amino Acidsreturn to top 

    A wide variety of amino acids are used to enhance physical performance.

    L-arginine, L-lysine, and L-ornithine are theorized to stimulate endogenous growth hormone release. These amino acids show up in lots of natural products claiming to be growth hormone stimulators...Natural Growth Hormone Formula, Growth Hormone Support, Doctor's A-Z GHR Growth Hormone Releaser, and many others.

    Some research shows that L-arginine and L-lysine can increase growth hormone release in humans.7820 However, L-ornithine does NOT increase growth hormone release.2418 Nonetheless, there is no reliable clinical research that L-arginine or L-lysine improves athletic performance. Some clinical research shows that L-ornithine does NOT improve athletic performance.2417,2418

    L-carnitine is used to improve fat metabolism and intracellular energy production. L-carnitine is essential for beta-oxidation of long-chain fatty acids in the mitochondria. To enter the mitochondria, fatty acids must bind to coenzyme A, forming fatty acyl-CoA. Long-chain fatty acyl-CoA molecules are too large to cross the internal mitochondrial membrane and rely on enzymatic transportation that requires L-carnitine. In the mitochondria, fatty acids undergo beta-oxidation to adenosine triphosphate (ATP) and L-acetyl-carnitine is excreted to begin a new transport cycle.12352

    Some clinical research suggests that L-carnitine might improve some aerobic processes and oxygen consumption.3649,3650 However, L-carnitine does NOT consistently improve athletic performance or endurance.1947,3639

    L-glutamine is used to enhance muscle development; however, preliminary research shows that it doesn't affect muscle precursor cells.13773 Clinical research shows that taking L-glutamine does not improve measures of athletic performance.2341,2342,5455,5456,5464,5465,5466

    Branched chain amino acids (BCAAs) are a group of essential amino acids including leucine, isoleucine, and valine. Taking branched-chain amino acids before exercise increases serum ammonia levels and appears to decrease muscle breakdown and inhibit muscle glycogen degradation during exercise.77,693,694

    Clinical trials have produced somewhat conflicting findings. Some research suggests that these amino acids might reduce muscle damage following intense exercise. However, most research shows that they do not improve athletic performance.

    		 
    View brands containing:
    -L-arginine
    -L-lysine
    -L-ornithine
      Question #8
    Which of the following are used for boosting endogenous growth hormone?
  • View brands containing:
    -L-carnitine
    -L-glutamine
    -Branched-chain amino acids
    Antioxidantsreturn to top 

    Antioxidants are often taken by athletes in an effort to prevent muscle damage and breakdown during exercise. Selenium, vitamin C, and vitamin E are commonly used antioxidants.

    Some clinical research shows that vitamin C might help prevent exercise-induced respiratory tract infections that can occur occasionally following intense exercise, such as running a marathon.9831 Population research also suggests that higher dietary intake of vitamin C is associated with improved physical performance in elderly patients.14006 But there is no reliable evidence that taking a vitamin C supplement improves athletic performance in young, healthy athletes.

    There is no reliable evidence that selenium or vitamin E have any effect on athletic performance.

    Pycnogenol is an extract from the bark of the French maritime pine tree. It contains several active flavonoids and phenol compounds with antioxidant activity. Some preliminary clinical research shows that taking pycnogenol 200 mg daily for 30 days significantly improves treadmill exercise capacity in recreational athletes.2554 Pycnogenol is well-tolerated and has not been linked to serious side effects in several short-term studies.

    		 
    View brands containing:
    -Selenium
    -Vitamin C
    -Vitamin E
    View brands containing:
    -Pycnogenol
    Endurance/Muscle/Metabolism/Energy Enhancersreturn to top 

    A long list of other substances are commonly used for improved energy, endurance, muscle, or metabolism.

    One common approach to improve endurance is the use of "blood doping" with erythropoietin, which increases hemoglobin and hematocrit. This has an effect similar to high-altitude training because it enhances the aerobic capacity of the body and might increase aerobic performance.16271,16273 High-altitude training is permitted, but the use of erythropoietin for this purpose is considered illegal.

    There are also significant safety concerns. The use of erythropoietin by cyclists is thought to have resulted in several cases of death from stroke, myocardial infarction, and pulmonary embolism.16274

    Iron supplements are also commonly used as a method for improving aerobic capacity and performance, but there is no reliable evidence to support this.

    Some athletes also use phosphodiesterase inhibitors such as sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra). These are normally used for erectile dysfunction and pulmonary hypertension. They increase oxygen supply in the body and blood flow to the lungs.

    Sodium bicarbonate is also used to improve endurance. It is thought to buffer lactic acid production from muscle and appears to delay muscle fatigue in aerobic and anaerobic exercises.16271

    Creatine is one of the best known sports supplements. Creatine is a normal component of skeletal muscle. In skeletal muscles creatine exists in dynamic equilibrium with phosphocreatine, which is a precursor to the energy molecule, adenosine triphosphate (ATP). Higher levels of creatine are thought to enhance the ability to renew ATP for short 10-20 second energy bursts and improve resynthesis of phosphocreatine during recovery from intense exercise. Taking creatine supplements enhances both creatine and phosphocreatine concentrations, providing a larger total creatine pool in the skeletal muscle.2103,3997,4574,4576,4580,4583,6925,6927,11330

    In addition to its role in ATP generation, preliminary research suggests creatine might increase the activity of muscle precursor cells called satellite cells, causing muscular hypertrophy.13773 But most research supports increased water retention as the primary cause of creatine-induced muscle gain.4569,4575,4576,4579,4588,6061,10062 Muscle enlargement due to increased water retention is short term. Creatine might allow athletes to train harder due to increased phosphocreatine resynthesis and subsequent energy production.6061 Creatine might also reduce lactate production, but this has not been consistently found in studies.4604,4592

    Clinical research shows that taking creatine enhances muscle performance during repeated bouts of brief, high-intensity exercise such as sprinting, resistance training, and power lifting.2100,2101,2102,4591,4592,4593,4594,4601,4602,4604,4605,6015,10064,11331 For other exercises, such as cycling, creatine appears to offer no benefit.4582,4595,4596,4597,4606,6183,13772

    Many variables seem to determine the effect of creatine on performance, including the person's training status, the type of sport being tested, diet, age of the person, and the dose of creatine. Creatine does not seem to improve performance in aerobic exercises, or benefit older individuals. Additionally, creatine does not seem to increase endurance or improve performance in highly trained athletes.2103,2105,2106,4607,13772

    Several creatine dosing regimens have been used. Most commonly loading doses of 20 grams/day (or 0.3 grams per kg) for 5 days, followed by 2 grams or more (0.03 grams per kg) daily, have been used.

    Practice Pearl
    Creatine can cause GI upset and about 25% of people experience muscle cramping.4584 People taking creatine should be advised to ensure adequate fluid intake to reduce cramping and prevent dehydration related to intracellular fluid shifts.4576

    Creatine has been linked to isolated reports of renal dysfunction.184,2118 But this appears to be rare in people with healthy kidneys.1368,2120,3996 Advise patients with existing kidney disease to avoid creatine supplements.

    Bee pollen is often promoted as a strength enhancer because of its combination of proteins, vitamins, fatty acids, and enzymes. However, clinical research shows that taking bee pollen does NOT improve athletic performance or endurance.7062,7063

    Choline is also promoted for increasing endurance, but clinical research shows that it does not reduce fatigue in athletes.5164

    Coenzyme Q-10 is thought to improve endurance by reducing fatigue. Coenzyme Q-10 is an important cofactor in many metabolic pathways, particularly in the production of adenosine triphosphate (ATP) in oxidative respiration. Therefore, it is thought to improve oxidative metabolism, resulting in improved exercise tolerance and decreased fatigue.8159,8162,8163

    Coenzyme Q-10 might improve exercise tolerance in patients with mitochondrial disorders or coenzyme Q-10 deficiency; however, it does not improve performance in athletes.2109,2110,8911

    Colostrum is popular now among athletes. It is the milk that newborn mammals consume from their mothers. Most athletes use powdered colostrum from cows, which contains proteins, fats, vitamins, minerals, growth factors, and high concentrations of immunoglobulin. Some researchers think that consuming colostrum might stimulate skeletal muscle growth and improve strength. It might also improve immunity and possibly resistance to stress. Some preliminary clinical research shows that taking colostrum for 8 weeks might improve peak power during anaerobic exercises such as sprints and high jumping.11453

    B vitamins including folic acid (vitamin B9), vitamin B1 (thiamine), vitamin B2 (riboflavin), niacin (vitamin B3), vitamin B5 (pantothenic acid), vitamin B6 (pyridoxine), and vitamin B12 (cyanocobalamin) are promoted for improving performance by improving aerobic capacity, enhancing energy, or increasing muscle growth. No reliable evidence supports the use of these B vitamins for improving athletic performance. In fact, preliminary clinical research suggests that taking thiamin plus pantothenic acid does not improve muscle strength or endurance in athletes.10431

    Phosphates are often used to increase energy and muscle endurance because phosphate is a key component of cellular energy, adenosine tri-PHOSPHATE. However, clinical research shows that taking phosphates does not significantly improve athletic performance.2499,8300,8301

    Pyruvate is a by-product of glucose metabolism. Some researchers have speculated that it might have a role in muscle development and reducing body fat; however, research shows that it does not affect muscle precursor cells.13773

    There are conflicting findings about the effects of pyruvate on athletic performance and body composition.

    Preliminary clinical research suggests that taking high dose pyruvate plus dihydroxyacetone increases arm and leg exercise endurance.807,808 However, other research suggests that pyruvate, alone or in combination with creatine does not improve athletic performance.13659,13661,13772

    Similarly, preliminary clinical research suggests that taking pyruvate in place of a portion of dietary carbohydrates and in combination with a low-calorie diet seems to help increase weight loss and decrease body fat.2472,2474,13658 Other research suggests pyruvate has no effect on body weight or body composition.13660

    D-ribose is a pentose sugar molecule which is involved in the metabolic pathways that help maintain adenosine triphosphate (ATP) levels. After intense exercise, muscle ATP is significantly lower. Athletes who take a D-ribose supplement, 200 mg/kg three times daily, have less ATP depletion following intense exercise. This suggests that ribose in muscle tissue is the limiting step in resynthesis of ATP; however, muscle ATP reduction does not appear to limit high-intensity exercise performance.15729

    Taking D-ribose supplements does not seem to significantly increase power output, anaerobic exercise, or improve muscle strength when used in doses ranging from 625 mg to 10 grams.15723,15724,15725,15726,15727,15728,15729

    		 
    View brands containing:
    -Iron
    -Creatine
    View brands containing:
    -Bee pollen
    -Choline
    -Coenzyme Q-10
    -Colostrum
    View brands containing:
    -Folic Acid
    -Vitamin B1
    -Vitamin B2
    -Niacin
    -Vitamin B5
    -Vitamin B6
    -Vitamin B12
    -Phosphates
    -Pyruvate
      Question #9
    Which of the following is correctly matched with its suspected mechanism of action?
  • View brands containing:
    -D-ribose
    The Bottom Linereturn to top 

    Both highly trained athletes and recreational or "weekend warrior" athletes frequently turn to athletic performance enhancing substances. The use of enhancing substances can be as simple as drinking a highly caffeinated energy drink to getting injections of prescription hormones.

    Only a handful of these substances have actually been shown to improve measures of athletic performance...caffeine, anabolic steroids, erythropoietin, sodium bicarbonate.

    Many of the enhancers are unsafe...stimulants, steroids and precursors, erythropoietin.

    Most research on "natural" performance enhancers has produced conflicting or negative findings, with only a couple exceptions.

    Some evidence supports the use of creatine for improving muscular power during repeated, short, maximal energy bursts. Some research suggests that pycnogenol might improve treadmill performance, but this is too preliminary.

    Most drugs and many natural medicines used to enhance athletic performance are not permitted in organized sports. Different agencies and organizations have different rules for which substances are prohibited. Help athletes steer clear from substances prohibited by their sporting organizations. Links to the most current prohibited lists for some of these organizations below:

    		 
      Question #10
    Which of the following substances has been shown to improve athletic performance?
  •   
     
    Recommendation Chart for Natural Medicines Used for Athletic Performance Enhancers *
    Safety/EffectiveLikely
    Safe    		Possibly
    Safe    		Insufficient
    Evidence    		Possibly
    Unsafe    		Likely
    Unsafe    		Unsafe
    Effective      
    Likely
    Effective    		      
    Possibly
    Effective
    -Caffeine
    -Creatine
    -Vitamin C
     
    -Pycnogenol
         		    
    Insufficient
    Evidence
    -Folic acid
    -Iron
    -Niacin
    -Oats
    -Selenium
    -Vitamin B1
    -Vitamin B2
    -Vitamin B5
    -Vitamin B6
    -Vitamin B12
    -Vitamin E
    -Colostrum
     
    -American ginseng
    -Cola nut
    -Green tea extract
    -Guarana
    -L-arginine
    -L-lysine
    -Mate
    -Pyruvate
         		 
    -Bitter orange
     
    -Ephedra
     
    -GHB
     
    Possibly
    Ineffective
    -Choline
    -D-ribose
     
    -Bee pollen
    -BCAAs
    -L-glutamine
    -Panax ginseng
    -Puncture vine
    -Siberian ginseng
    -Chrysin
     
    -L-ornithine
     
    -Androstenediol
    -DHEA
         		  
    Likely
    Ineffective
    -Phosphates
    -Coenzyme Q-10
    -L-carnitine
         		  
    -Androstenedione
         		  
    Ineffective      
     KEY:
     Consider recommending this product.
     Don't recommend using this product.
     Recommend against using this product.

    * These proposed recommendations are based solely on the Safety and Effectiveness Ratings contained in Natural Medicines Comprehensive Database. This assumes use of high-quality, uncontaminated products and the use of typical doses. Keep in mind that some products are never appropriate for some patients due to concomitant disease states, potential drug interactions, or other clinical factors. Use your clinical judgment before recommending any product.

    References return to top
    77Blomstrand E, Ek S, Newsholme EA. Influence of ingesting a solution of branched-chain amino acids on plasma and muscle concentrations of amino acids during prolonged submaximal exercise. Nutrition 1996;12:485-90.
    184Koshy KM, Griswold E, Schneeberger EE. Interstitial nephritis in a patient taking creatine. N Engl J Med 1999;340:814-5.
    693MacLean DA, Graham TE. Branched-chain amino acid supplementation augments plasma ammonia responses during exercise in humans. J Appl Physiol 1993;74:2711-7.
    694MacLean DA, Graham TE, Saltin B. Branched-chain amino acids augment ammonia metabolism while attenuating protein breakdown during exercise. Am J Physiol 1994;267:E1010-22.
    797Awang DVC. Siberian ginseng toxicity may be case of mistaken identity (letter). CMAJ 1996;155:1237.
    807Stanko RT, Robertson RJ, Galbreath RW, et al. Enhanced leg exercise endurance with a high-carbohydrate diet and dihydroxyacetone and pyruvate. J Appl Physiol 1990;69:1651-6.
    808Stanko RT, Robertson RJ, Spina RJ, et al. Enhancement of arm exercise endurance capacity with dihydroxyacetone and pyruvate. J Appl Physiol 1990;68:119-24.
    1365Wallace MB, Lim J, Cutler A, Bucci L. Effects of dehydroepiandrosterone vs androstenedione supplementation in men. Med Sci Sports Exerc 1999;31:1788-92.
    1368Greenhaff P. Renal dysfunction accompanying oral creatine supplements. Lancet 1998;352:233-4.
    1381FDA Takes Aim at Ephedra. The Washington Post. Available at: www.washingtonpost.com/wp-dyn/articles/A33439-2000Mar17.html (Accessed 19 March 2000).
    1427Vogler BK, Pittler MH, Ernst E. The efficacy of ginseng. A systemic review of randomized clinical trials. Eur J Clin Pharmacol 1999;55:567-75.
    1905Broeder CE, Quindry J, Brittingham K, et al. The Andro Project: physiological and hormonal influences of androstenedione supplementation in men 35 to 65 years old participating in a high-intensity resistance training program. Arch Intern Med 2000;160:3093-104.
    1947Colombani P, Wenk C, Kunz I, et al. Effects of L-carnitine supplementation on physical performance and energy metabolism of endurance-trained athletes: a double-blind crossover field study. Eur J Appl Physiol 1996;73:434-9.
    2040Penzak SR, Jann MW, Cold JA, et al. Seville (sour) orange juice: synephrine content and cardiovascular effects in normotensive adults. J Clin Pharmacol 2001;41:1059-63.
    2100Kreider RB, Ferreira M, Wilson M, et al. Effects of creatine supplementation on body composition, strength, and sprint performance. (abstract) Med Sci Sports Exerc 1998;30:73-82.
    2101Vandenberghe K, Goris M, Van Hecke P, et al. Long-term creatine intake is beneficial to muscle performance during resistance training (abstract). J Appl Physiol 1997;83:2055-63.
    2102Earnest CP, Snell PG, Rodriguez R, et al. The effect of creatine monohydrate ingestion on anerobic power indices, muscular strength and body composition. Acta Physiol Scand 1995;153:207-9.
    2103Balsom PD, Soderland K, Ekblom B. Creatine in humans with special reference to creatine supplementation. Sports Med 1994;18:268-80.
    2105Burke LM, Pyne DB, Telford RD. Oral creatine supplementation does not improve sprint performance in elite swimmers. Med Sci Sports Exerc 1995;27:S146.
    2106Mujika I, Chatard J, Lacoste L, et al. Creatine supplementation does not improve sprint performance in competitive swimmers. Med Sci Sports Exerc 1996;28:1435-41.
    2109Malm C, Svensson M, Ekblom B, et al. Effects of ubiquinone-10 supplementation and high intensity training on physical performance in humans. Acta Physiol Scand 1997;161:379-84.
    2110Weston SB, Zhou S, Weatherby RP, et al. Does exogenous coenzyme Q10 affect aerobic capacity in endurance athletes? Int J Sport Nutr 1997;7:197-206.
    2118Pritchard NR, Kalra PA. Renal dysfunction accompanying oral creatine supplements. Lancet 1998;351:1252-3.
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