Why athletes take tadalafil

Tadalafil is a type 5 phosphodiesterase inhibitor, known primarily as a drug for treating erectile dysfunction. Yet in the sporting world it is discussed far more broadly: as a means for «better blood flow», endurance at altitude and even «protecting» the body during cycles. The editors examined which of these expectations have a scientific basis and which remain guesswork.

Why tadalafil entered sporting conversations

Tadalafil blocks the enzyme phosphodiesterase 5 (PDE-5), which breaks down cyclic guanosine monophosphate (cGMP) in vascular smooth muscle. When cGMP accumulates, the vascular wall relaxes and blood flow in the corresponding area increases. PDE-5 is most abundant in the corpora cavernosa of the penis, in the vessels of the lungs and in the smooth muscle of the urinary tract — hence the drug's registered indications.

Tadalafil differs from sildenafil primarily in duration of action. Its half-life in healthy people is about 17.5 hours, so the effect can persist for up to 36 hours. It is precisely this «long» pharmacokinetics that made the drug of interest to people seeking daily support of vascular tone rather than a one-off effect.

In the sporting world the logic is simple: if the drug dilates vessels, then perhaps it will improve the delivery of oxygen and nutrients to muscle, boost the «pump» during training and speed recovery. This idea is intuitively clear, but the physiology of a working muscle is arranged more complexly than it seems.

Another reason for its popularity is medical indications that really occur in older athletes: erectile dysfunction and symptoms of benign prostatic hyperplasia. Finally, tadalafil is often mentioned in the context of anabolic steroid use, which will be discussed separately.

«The pump» and blood flow in muscle: what is known

During intense work, blood flow in skeletal muscle is regulated primarily by local metabolic signals: the accumulation of adenosine, potassium and hydrogen ions, and a drop in oxygen levels. These mechanisms can increase muscle perfusion tens of times over compared with rest. Against this backdrop the additional effect of a PDE-5 inhibitor in a healthy person is most likely small.

Studies of tadalafil's effectiveness in healthy athletes under ordinary conditions (without hypoxia) are few and small. Italian work on trained men studied primarily the hormonal responses to exercise and individual measures of anaerobic performance; no convincing gain in results was shown. There are no large randomized studies proving improved strength or hypertrophy.

The feeling of «a better pump» that users describe may be real on a subjective level, but by itself it does not mean a greater gain in muscle mass. The filling of muscle with blood during a set is a temporary phenomenon, and the link between its magnitude and long-term hypertrophy is unproven.

Below the editors have summarized the main expectations and the level of evidence for them.

Thus it is precisely in «classic» strength sport that expectations of tadalafil diverge most from the data. This does not mean there is guaranteed to be no effect, but speaking of it as an established fact is incorrect.

Altitude and hypoxia: where the data really are

The strongest scientific basis for PDE-5 inhibitors in physically active people concerns mountain conditions. In hypoxia the pulmonary vessels reflexively narrow, pressure in the pulmonary artery rises, and in susceptible people high-altitude pulmonary edema — a life-threatening condition — can develop.

In a randomized study by Maggiorini and colleagues (2006) in people prone to high-altitude pulmonary edema, tadalafil, like dexamethasone, reduced the incidence of this complication during a rapid ascent to about 4,500 m. This is a medical, preventive effect, not an increase in athletic performance.

For sildenafil there are data on improved exercise tolerance in hypoxia (Ghofrani et al., 2004), including at Everest base camp. Tadalafil has a similar mechanism, so these results are often transferred to it as well, although direct comparisons are few.

For athletes at sea level these results mean little: in normoxia pulmonary blood flow is not the main limitation of performance in healthy people. Moreover, any use of a prescription drug in the mountains must be agreed with a doctor, since hypotension at altitude can be dangerous.

Tadalafil against the backdrop of anabolic steroids

On sports forums tadalafil is often mentioned alongside anabolic steroids. There are two reasons. The first is sexual dysfunction after suppression of one's own testosterone: during androgen use or after their withdrawal many men face reduced libido and erection.

The second reason is the widespread belief that the drug «protects» the heart, vessels or prostate from steroid side effects. There is no clinical evidence for such a claim. Tadalafil does not normalize the lipid profile, does not lower hematocrit and does not correct hormonal imbalance.

It is important that erectile dysfunction in a young man is a symptom that requires a search for the cause. Masking it with a pill without tests can delay the diagnosis of hypogonadism, cardiovascular disorders or metabolic problems.

• Tadalafil does not affect the level of testosterone, LH or FSH enough to restore the hormonal system.
• It does not lower hematocrit or blood viscosity, which often rise on androgens.
• It does not eliminate the cause of erectile dysfunction, only relieves the symptom.
• Combination with some substances that circulate among athletes (nitrates, «poppers», alpha-blockers) can cause dangerous hypotension.

It is worth noting separately: on the illegal market tadalafil is often sold under the guise of «sports boosters» or «natural» libido supplements. Regulators have repeatedly found undeclared PDE-5 inhibitors in such products, which creates a risk for people taking nitrates.

Anti-doping status and medical risks

As of the current editions of the WADA Prohibited List, PDE-5 inhibitors are not on it. However, the list is updated every year, so a competing athlete must check the current edition independently and, if necessary, consult the team doctor.

Absence from the prohibited list does not mean safety. The most frequent side effects of tadalafil are headache, dyspepsia, back and muscle pain, nasal congestion and facial flushing. Back pain and myalgia are attributed, in particular, to a partial effect on PDE-11, which can interfere with training.

The most serious risk is a sharp drop in blood pressure when combined with nitrates. The drug's package insert directly contraindicates such a combination. Among rare but important complications are priapism, sudden loss of vision (non-arteritic anterior ischemic optic neuropathy) and sudden hearing loss.

For people with cardiovascular disease, any sexual or physical activity while on the drug requires prior evaluation by a cardiologist. This also applies to veteran athletes, in whom coronary artery disease may run its course without symptoms.

Editorial conclusions

Tadalafil is an effective drug with clear medical indications: erectile dysfunction, BPH symptoms and pulmonary arterial hypertension. Its mechanism of action is indeed linked to vasodilation, but this does not make it a means for growing strength or muscle mass.

The most convincing data on PDE-5 inhibitors in physically active people concern mountain conditions and the prevention of high-altitude pulmonary edema. In classic strength and power sports there is no evidence of benefit.

Using tadalafil for «protection» during anabolic steroid use has no scientific basis and can mask symptoms that require examination.

We also recommend reading our materials on the side effects and contraindications of tadalafil, on its interactions with other drugs and on common myths about this substance.

References

1. Eli Lilly and Company. Cialis (tadalafil) tablets: prescribing information. Indianapolis; U.S. Food and Drug Administration label.
2. Forgue ST, Patterson BE, Bedding AW, et al. Tadalafil pharmacokinetics in healthy subjects. Br J Clin Pharmacol. 2006;61(3):280–288.
3. Maggiorini M, Brunner-La Rocca HP, Peth S, et al. Both tadalafil and dexamethasone may reduce the incidence of high-altitude pulmonary edema: a randomized trial. Ann Intern Med. 2006;145(7):497–506.
4. Ghofrani HA, Reichenberger F, Kohstall MG, et al. Sildenafil increased exercise capacity during hypoxia at low altitudes and at Mount Everest base camp: a randomized, double-blind, placebo-controlled crossover trial. Ann Intern Med. 2004;141(3):169–177.
5. Pope HG Jr, Wood RI, Rogol A, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341–375.
6. World Anti-Doping Agency. International Standard: Prohibited List. Montreal: WADA; оновлюється щороку.