The benefits of 5-HTP for athletes: the evidence base

5-HTP increasingly appears in the sports nutrition range with promises of better sleep, recovery and "appetite control during a cut." But sport is a special situation: serotonin in the brain is closely linked to the feeling of fatigue during exercise. The editors analyzed what is known about the effect of 5-HTP specifically on athletes and whether there are grounds to consider it beneficial.

Serotonin and central fatigue

Fatigue during prolonged work arises not only in the muscles. Back in the 1980s, Newsholme and colleagues formulated the central fatigue hypothesis: during prolonged exertion the entry of free tryptophan into the brain increases, serotonin synthesis rises, and this heightens the feeling of fatigue, drowsiness and reduced motivation (Newsholme, Blomstrand, 2006).

The mechanism is as follows: during prolonged work the concentration of free fatty acids in the blood rises, they displace tryptophan from its binding to albumin, and the level of branched-chain amino acids (BCAAs), which compete with tryptophan for transport into the brain, falls. As a result, more tryptophan enters the brain.

The hypothesis was later refined: what matters is not the absolute level of serotonin but the ratio of serotonin to dopamine. A high ratio is associated with fatigue, a low one with the maintenance of motivation and motor activity (Davis, Bailey, 1997; Meeusen et al., 2006).

In this context 5-HTP looks not like an ally but like a potential adversary of endurance: it directly increases serotonin synthesis, bypassing the regulatory mechanisms that at least somewhat limit the process when tryptophan is taken.

What studies say about endurance

There are practically no direct high-quality studies of the ergogenic action of 5-HTP in athletes. The most informative are works in which serotonergic activity was enhanced pharmacologically. Wilson and Maughan (1992) gave volunteers paroxetine — a serotonin reuptake inhibitor — and recorded a shortening of the time to exhaustion during cycling compared with placebo.

Similar results were obtained in other experiments with serotonergic drugs: in a number of works their intake worsened endurance performance or increased the subjective perception of effort. At the same time, not all studies are unambiguous, and the review by Meeusen and colleagues (2006) emphasizes that central fatigue is a multifactorial phenomenon that cannot be reduced to serotonin alone.

The "reverse" logic also did not work as expected. BCAA supplements, intended to reduce the entry of tryptophan into the brain, did not improve endurance results in most studies, although they could reduce the subjective feeling of fatigue.

Thus, as of today there are no data that would indicate a benefit of 5-HTP for endurance, and physiological reasoning and pharmacological experiments rather point to a risk of worsening. The editors do not recommend taking 5-HTP before prolonged workouts or competitions.

Appetite and body weight control

The most common sports argument in favor of 5-HTP is appetite control during weight loss, for example before competitions in weight classes or in bodybuilding. It relies on the study by Cangiano and colleagues (1992), in which people with obesity on 5-HTP consumed fewer calories, especially carbohydrates, and felt satiety faster.

However, these works had small samples, were conducted on people with obesity rather than athletes, and part of the effect could be provided by side effects — nausea and stomach discomfort, which also reduce appetite. There are no independent large studies that would confirm the results.

For an athlete in a calorie deficit, reduced appetite is not only a plus. Excessive carbohydrate restriction worsens training quality, and combining 5-HTP with caffeine "fat burners" and other substances can create unpredictable effects.

Far more reliable tools for controlling hunger during a deficit are sufficient protein intake, fiber, high-volume low-calorie foods, and a sleep routine. It is precisely these that sports nutrition position papers recommend.

Sleep, mood and recovery

Since serotonin is a precursor of melatonin, 5-HTP is advertised as a remedy for sleep and recovery. The editors did not find studies that would show an improvement in sleep in athletes after taking 5-HTP. Data on sleep in the general population are also limited and of low quality.

As for mood: the Cochrane review by Shaw and colleagues (2002) found the evidence base regarding depression insufficient, and the meta-analysis by Javelle and colleagues (2020) found it to be of low quality. For athletes with signs of overtraining or depressive symptoms, the correct step is to see a doctor, not a supplement.

As for "recovery" in the sense of muscle regeneration — there are no mechanistic grounds for such an effect. 5-HTP does not affect muscle protein synthesis or glycogen recovery.

It is also important to remember: many athletes take antidepressants, tramadol for injuries or triptans for migraine. Combining these drugs with 5-HTP carries a risk of serotonin syndrome (Boyer, Shannon, 2005).

Assessing the evidence and practical conclusions

The consensus statement of the International Olympic Committee on dietary supplements (Maughan et al., 2018) singles out a small group of supplements with proven effectiveness for performance: caffeine, creatine, nitrates, beta-alanine, sodium bicarbonate. 5-HTP is not among them and is not considered an ergogenic aid.

In summary, the evidence base for 5-HTP in sport can be described as follows:

• Endurance:no benefit shown, theoretically possible worsening.
• Strength and muscle mass:no mechanism and no studies.
• Appetite:small studies in people with obesity; not studied in athletes.
• Sleep and mood:data insufficient and of low quality.

For athletes who undergo doping control, an additional factor is product quality. 5-HTP itself is not banned by WADA, but supplements may be contaminated; products certified under independent testing programs reduce this risk.

If an athlete is nonetheless considering 5-HTP, for example for appetite control, this decision should be made together with a doctor or sports dietitian, taking into account all the medications and supplements they take.

Editorial conclusions

For athletes, 5-HTP has no proven benefits. The serotonin hypothesis of central fatigue and pharmacological experiments indicate that enhancing serotonergic activity may worsen endurance.

The only direction with some data — appetite reduction — was studied in people with obesity and in small studies, so transferring it to sport is incorrect.

Reliable alternatives for endurance, sleep and appetite control are nutrition, routine, and supplements with proven effectiveness.

Related materials: "5-HTP: what it is and how it works," "Side effects of 5-HTP" and "Myths about L-tyrosine."

References

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2. Davis JM, Bailey SP. Possible mechanisms of central nervous system fatigue during exercise. Med Sci Sports Exerc. 1997;29(1):45–57.
3. Meeusen R, Watson P, Hasegawa H, et al. Central fatigue: the serotonin hypothesis and beyond. Sports Med. 2006;36(10):881–909.
4. Wilson WM, Maughan RJ. Evidence for a possible role of 5-hydroxytryptamine in the genesis of fatigue in man: administration of paroxetine, a 5-HT re-uptake inhibitor, reduces the capacity to perform prolonged exercise. Exp Physiol. 1992;77(6):921–924.
5. Cangiano C, Ceci F, Cascino A, et al. Eating behavior and adherence to dietary prescriptions in obese adult subjects treated with 5-hydroxytryptophan. Am J Clin Nutr. 1992;56(5):863–867.
6. Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7):439–455.
7. Shaw K, Turner J, Del Mar C. Tryptophan and 5-hydroxytryptophan for depression. Cochrane Database Syst Rev. 2002;(1):CD003198.
8. Boyer EW, Shannon M. The serotonin syndrome. N Engl J Med. 2005;352(11):1112–1120.