The effects of tadalafil last up to 36 hours. Tadalafil is a prescription medication that is commonly used to treat erectile dysfunction in men. Tadalafil is a long-acting medication, and clinical studies have shown that the effects of the drug last up to 36 hours after taking tadalafil, with the optimal duration of effectiveness being within 28 hours. Taking tadalafil is prone to adverse reactions such as headache, dizziness, flushing, nausea, muscle pain and nasopharyngitis, but symptoms are generally mild. The concomitant use of tadalafil with theophylline may lead to increased heart rate, and use with alcohol may increase the risk of low blood pressure, so tea and alcohol should be avoided during medication to avoid adverse reactions. People for whom tadalafil is contraindicated include patients with heart disease, epilepsy, and those who are allergic to tadalafil ingredients. If there is a need to take tadalafil, patients should be under the guidance of a doctor, and should not take the drug on their own to avoid adverse effects.