Tadalafil
Tadalafil is a long-acting selective PDE5 inhibitor used for erectile dysfunction, benign prostatic hyperplasia and pulmonary arterial hypertension. Its 17-hour half-life supports an effect window of up to 36 hours. Available under brand and generic names.
- Chemical formula
- C22H19N3O4
- CAS number
- 171596-29-5
- ATC code
- G04BE08
- Molecular weight
- 389.4 g/mol
- Drug class
- PDE5 inhibitor
- Also known as
- IC351, GF196960
What is it?
Tadalafil is a small-molecule selective phosphodiesterase type 5 inhibitor first approved in 2003 for erectile dysfunction in adult men. It was developed by Glaxo Wellcome and ICOS Corporation under the code IC351 and is marketed by Eli Lilly under the brand name Cialis. Compared with earlier PDE5 inhibitors, tadalafil's defining feature is a substantially longer half-life, which translates into an extended therapeutic window and supports daily-dose regimens at lower strengths.
Mechanism of action
Tadalafil selectively inhibits PDE5, the enzyme responsible for breaking down cyclic guanosine monophosphate in the corpus cavernosum and other vascular smooth muscle. By blocking PDE5, the molecule allows cGMP — produced when nitric oxide is released during sexual stimulation — to accumulate. This relaxes vascular smooth muscle, increases local blood flow and supports erection. The same mechanism explains tadalafil's approved use in pulmonary arterial hypertension and lower urinary tract symptoms associated with benign prostatic hyperplasia.
Pharmacokinetics
After oral administration tadalafil reaches peak plasma concentrations in approximately two hours. Absorption is not significantly affected by food. The molecule is metabolised in the liver via CYP3A4 and eliminated mainly through the faeces. The terminal half-life is approximately 17.5 hours — substantially longer than sildenafil's three to five hours — which gives an effect window of up to 36 hours after a single dose. This extended profile supports both on-demand and once-daily low-dose regimens.
Indications
Tadalafil is approved for three indications: erectile dysfunction in adult men, lower urinary tract symptoms associated with benign prostatic hyperplasia, and pulmonary arterial hypertension. The dosing schedule and approved strength differ between indications. The molecule is not approved for use in women, paediatric patients or as a recreational stimulant. According to the prescribing information, off-label use should be discussed with a qualified healthcare professional before initiation.
Safety profile
Common adverse effects in clinical trials include headache, dyspepsia, back pain, myalgia, nasal congestion and facial flushing. Back and muscle pain occur more frequently with tadalafil than with shorter-acting PDE5 inhibitors and typically appear 12 to 24 hours after dosing. Serious but rare events include sudden hearing loss and priapism. Concurrent use of organic nitrates or guanylate cyclase stimulators is contraindicated. According to the prescribing information, cardiovascular fitness and current medications must be reviewed before treatment.
Products containing this ingredient
Frequently asked questions
How is tadalafil different from sildenafil? ▾
Both are selective PDE5 inhibitors used for erectile dysfunction, but their pharmacokinetic profiles differ. Tadalafil has a half-life of about 17.5 hours, supporting an effect window of up to 36 hours after a single dose. Sildenafil's half-life is three to five hours, with an effect lasting up to four hours. Tadalafil also has approved indications beyond erectile dysfunction (BPH, pulmonary arterial hypertension), while sildenafil is approved for ED and pulmonary hypertension at separate strengths.
What is the 36-hour window? ▾
The 36-hour figure refers to the time during which most adult men can expect tadalafil to remain pharmacologically active after a single on-demand dose, according to clinical trial data. It does not mean a continuous erection — sexual stimulation is still required for the medication to produce an effect. The extended window means the timing of sexual activity does not need to be planned around a narrow drug onset, which is the marketing point behind the 'weekend pill' description.
Can tadalafil be taken daily? ▾
Yes. A 2.5mg or 5mg once-daily formulation is approved for ongoing treatment of erectile dysfunction and BPH. Daily dosing produces steady plasma concentrations and removes the need to plan around individual doses. According to the prescribing information, the choice between on-demand (10mg or 20mg) and daily (2.5mg or 5mg) regimens depends on frequency of sexual activity, BPH symptoms, tolerability and clinician judgement.
Does food affect tadalafil absorption? ▾
No. Unlike sildenafil, the absorption of tadalafil is not significantly affected by food, including high-fat meals. This is a clinical advantage when timing is uncertain. Alcohol in moderate amounts is unlikely to alter the pharmacokinetics, but heavy intake may reduce blood pressure further when combined with tadalafil and may impair erectile response on its own. According to the prescribing information, alcohol should be used cautiously.
What are the main contraindications for tadalafil? ▾
The most important contraindication is concurrent use of organic nitrates or guanylate cyclase stimulators (such as riociguat), where the combination can cause severe hypotension. Other situations requiring caution include severe hepatic impairment, recent stroke or heart attack, low blood pressure, severe cardiovascular disease, and known hypersensitivity to the molecule. According to the prescribing information, a clinician should review medical history before any prescription.
The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.