You should not take 40 mg of tadalafil a day, and you should not take more than 20 mg of tadalafil a day. Tadalafil tablets are used to treat erectile dysfunction in men who need sexual stimulation for the product to take effect. The recommended dose of this product is 10 mg, with a maximum amount of 20 mg, and the maximum frequency of dosing is once a day, so you should not take 40 mg a day. The use of tadalafil may cause adverse reactions such as headache, back pain, and indigestion. If you take 40 mg a day, it may lead to an increased incidence of these adverse reactions. Tadalafil is contraindicated in people who are allergic to any of the ingredients in this product, patients who are taking any form of nitrates, guanylate cyclase stimulators, women, children and other people. The above medicines should be used under the supervision of a doctor.