Tadalafil is usually effective in about 30 minutes after use, and is used on an as-needed basis, taken at least half an hour before sexual activity. Tadalafil belongs to the inhibitor class of cyclic guanosine monophosphate type 5 phosphodiesterase, which can increase the level of cyclic guanosine monophosphate in the corpus cavernosum to make the penis erect when there is sexual stimulation. It is used clinically to treat erectile dysfunction. Tadalafil can be effective about half an hour after use, the onset of action may vary from person to person, and the average maximum blood concentration is reached in about 2 hours. It is usually taken as needed, at least half an hour before sexual activity and up to once a day. Tadalafil is not used in women and should not be combined with nitrates such as isosorbide nitrate, as this may cause low blood pressure. Due to the potential risk of sexual activity in patients with heart disease, it should be used with caution in those with underlying cardiovascular disease and prior consultation with a cardiologist is recommended. Side effects such as headache, flushing, back pain and myalgia may occur after tadalafil use. If you feel unwell, you should consult your doctor promptly.