Tadalafil takes effect in about half an hour after taking it, and reaches maximum blood concentration in 2 hours, and is recommended to be taken at least half an hour before sexual activity. Tadalafil is a selective inhibitor of cyclic guanosine monophosphate type 5 phosphodiesterase, which promotes relaxation of cavernous smooth muscle, blood flow into penile tissue, and penile erection in the presence of sexual stimulation. It is used clinically to treat erectile dysfunction. Tadalafil takes effect about 30 minutes after administration and reaches the average maximum blood concentration in about 2 hours. Tadalafil is usually taken as needed and used at least half an hour before sexual activity. Tadalafil should not be combined with nitrates such as isosorbide dinitrate. It should be used with caution in individuals with underlying cardiovascular disease due to the potential cardiac risks associated with sexual activity. Tadalafil use may cause adverse reactions such as headache, dyspepsia, back pain and myalgia. If you feel unwell, you should consult your doctor.