Tadalafil

Overview

Tadalafil is a synthetic, orally active small molecule, not a peptide. It inhibits phosphodiesterase type 5 (PDE5) and is the active substance in prescription products including Cialis and Adcirca, as well as generics. The brand names are not interchangeable shorthand for every indication: Cialis-type labels cover erectile dysfunction (ED) and benign prostatic hyperplasia (BPH), while Adcirca-type labels cover pulmonary arterial hypertension (PAH).

Tadalafil has extensive randomized human evidence and regulator-reviewed product information. That does not make it a general-purpose “blood-flow,” libido, testosterone, metabolic or longevity compound. Benefits and risks depend on the diagnosed condition, the particular product and the person’s cardiovascular status and other medicines.

Verified identity

PubChem records tadalafil as CID 110635, molecular formula C22H19N3O4, molecular weight 389.4 g/mol, CAS 171596-29-5 and UNII 742SXX0ICT. It has a defined organic structure and no amino-acid sequence. Its appearance in PeptideGuide does not make the molecule a peptide.

The two PeptideGuide rows disagreed about category, expanded name and several claim fields. More importantly, their only PMID lead—15016503—is a paper on soil nematodes, not tadalafil. None of those source-row claims was used as medical evidence here.

Mechanism: what PDE5 inhibition does

During sexual stimulation, nitric oxide increases cyclic guanosine monophosphate (cGMP) in penile tissue. PDE5 breaks down cGMP. By inhibiting PDE5, tadalafil prolongs cGMP signalling and can support smooth-muscle relaxation and blood inflow. The medicine does not create sexual stimulation and is not a testosterone or libido treatment.

PDE5 is also present in pulmonary vasculature. In PAH, PDE5 inhibition can increase cGMP-mediated vasodilation and lower pulmonary vascular resistance. For BPH symptoms, current labels acknowledge that the precise cellular mechanism is not fully established; symptom improvement should not be rewritten as proof that tadalafil shrinks the prostate or cures the underlying disease.

Approved uses and evidence

Erectile dysfunction

Current US and EU product information supports tadalafil for ED. Randomized, double-blind trials found improvements over placebo in validated erectile- function measures and successful-intercourse outcomes. The US label states that more than 9,000 men received tadalafil in its worldwide clinical-trial programme. These results establish efficacy for the labelled condition, not a promise of response for every individual or evidence of increased desire.

Benign prostatic hyperplasia

Tadalafil is also approved for the signs and symptoms of BPH, including when ED is present. Twelve-week randomized trials found better International Prostate Symptom Score (IPSS) changes than placebo. IPSS is a patient-reported symptom measure: improvement does not by itself show a reduction in prostate size, remove the need to investigate other causes of urinary symptoms or demonstrate prevention of urinary retention or surgery.

Pulmonary arterial hypertension

Separate tadalafil products are approved for PAH. In the randomized PHIRST trial, the approved high-dose arm improved six-minute walking distance versus placebo and reduced clinical-worsening events over the trial period. PAH is a serious specialist diagnosis; its product label, dose and risk assessment are different from ED/BPH treatment.

Pharmacokinetics

The current US label reports a mean terminal half-life of 17.5 hours in healthy subjects and predominant hepatic metabolism by CYP3A4. This helps explain the longer exposure window compared with some other PDE5 inhibitors, but it does not mean a fixed duration of effect for every person.

Potent CYP3A4 inhibitors can raise tadalafil exposure, while CYP3A4 inducers can lower it. Kidney or liver impairment can materially change the permitted regimen or make once-daily use unsuitable. These are prescribing decisions, not details to infer from a generic internet dosing chart.

Safety and interaction boundaries

The current ED/BPH label lists headache, dyspepsia, back pain, myalgia, nasal congestion, flushing and limb pain among common adverse reactions. Important warnings include:

• hypotension with nitrates, riociguat, alpha-blockers, antihypertensives or substantial alcohol intake;
• cardiovascular risk when sexual activity itself is medically inadvisable;
• an erection lasting more than four hours, which needs emergency care;
• sudden vision loss or sudden hearing decrease/loss, which requires prompt medical assessment;
• higher exposure with potent CYP3A4 inhibitors; and
• product-specific restrictions in kidney or liver impairment.

The label does not prove that every reported post-marketing event was caused by tadalafil, but rare-event uncertainty is not a reason to omit the warning.

Russian-language and Russia-origin evidence pass

Russian sources added context but did not overturn the regulator and randomized trial evidence:

• A 2014 review (PMID 25140232) described Russian practice and reported a January 2012 Russian approval for once-daily use in LUTS/BPH. It was a review, and some authors were affiliated with the manufacturer; it is not an independent pivotal trial.
• A 2021 Russian-language paper (PMID 33818935) examined Tadalafil-SZ and endothelial-function measures in men with ED. Its local study design and surrogate endpoints do not justify a general cardiovascular-protection claim.
• A Russia-affiliated combination study of dutasteride, tadalafil and solifenacin (PMID 35198395) cannot isolate tadalafil’s effect. The journal later published a corrigendum (PMID 36721689), so the correction must accompany any use of that paper.
• Russian web and catalog searches also exposed small, product-specific and non-indexed reports. They were retained in the dossier as leads, not promoted above current regulator labels or controlled international trials.

This lane prevents English-only source bias while keeping study design, independence and corrections visible.

Sport and WADA

The indexed text of WADA’s 2026 Prohibited List reviewed for this article did not specifically name tadalafil, PDE5 inhibitors or phosphodiesterase-5. That bounded result does not infer an S0 or other WADA class and is not a permission statement. Athletes remain responsible for the current list, their governing rules and the actual contents of any product.

Product quality matters

Regulator approval applies to authorised products, not to every tablet sold as “tadalafil.” FDA has identified counterfeit Cialis and products with hidden tadalafil. Undeclared or counterfeit products create additional uncertainty about identity, dose and contaminants, and do not inherit the benefit–risk assessment of a licensed medicine.

Evidence bottom line

Tadalafil is a well-characterised, non-peptide prescription medicine with substantial human evidence for specific approved indications. The most important reading discipline is to keep those indications separate, avoid turning symptom outcomes into cure claims and treat nitrate/riociguat and cardiovascular interactions as core facts—not fine print.