Tadalafil has the benefit of treating erectile dysfunction in men. During sexual stimulation, the penis becomes erect as a result of increased blood flow to the penis caused by relaxation of the penile arteries and penile cavernous smooth muscle. This response is mediated by the release of nitric oxide (NO) from nerve endings and endothelial cells. NO stimulates smooth muscle cells to synthesize cyclic guanosine monophosphate (cGMP), and cGMP leads to smooth muscle relaxation and increased penile corpus cavernosum blood flow. Tadalafil inhibits phosphodiesterase 5 (PDE5) and enhances erectile function by increasing cGMP. Adverse effects of tadalafil include headache, dyspepsia, allergic reactions, stroke, and myocardial infarction. The drug can enhance the antihypertensive effect of nitrates, so it is strictly prohibited to take with nitrates, and should not be used in patients with heart disease who should not be sexually active. It should also not be used in patients with unstable angina or who have had a stroke in the past 6 months. Although tadalafil has a therapeutic effect on erectile dysfunction in men, it should always be taken under the supervision of a physician.