Tadalafil is a prescription medication for the treatment of erectile dysfunction in men, and usually an erection occurs with sexual stimulation after the medication, which can last for about 20 minutes. Specific adverse reactions may occur that may result in a persistent erection for even more than 4 hours or more. Some patients may have no effect or poor effect. 1. Normal condition: Under normal circumstances, after the use of the drug, the penile erection can be maintained for about 20 minutes during sex, which can effectively improve the patient’s sexual life experience. 2. Persistent erection: some patients will have persistent erection after taking tadalafil, also known as abnormal erection, the erection time can be more than 4 hours, need to go to the hospital in time for examination and treatment. 3. No effect: some patients have penile arteriovenous fistula, in this case the use of tadalafil has no effect, or the effect is not good. Tadalafil is a prescription drug with certain side effects and indications, and needs to be used under the guidance of a doctor in order to achieve more satisfactory results.