Taking sildenafil without intercourse usually has no effect. Because after taking sildenafil usually need to have sexual stimulation under the premise in order to make the penis erect, after taking the drug if there is no sex, the drug will be metabolized with time, and will not have an effect on the erection of the penis, the same will not jeopardize the health of the body. Common adverse reactions to sildenafil tablets are mainly headache, flushing, dizziness, nasal congestion, indigestion, visual abnormalities and so on. This drug is contraindicated for women, people who are allergic to this product, children, and people whose recent cardiovascular status makes them unfit for sexual intercourse. Sildenafil as a prescription drug, it is best to take medication and treatment under the guidance of a doctor to avoid jeopardizing your health, in addition, sildenafil can not be taken with any nitrate drugs, which may be life-threatening.