Viagra, whose generic name is sildenafil citrate, does not have a definite time to take it, so there is no such thing as it being best taken at night. Sildenafil citrate has a definite therapeutic effect on men suffering from erectile dysfunction, but sildenafil citrate itself has no libido-promoting effect, and the drug only works after being sexually stimulated after taking the drug, and sexual stimulation is not limited to the nighttime, so there is no such thing as the claim that it is best to take it at night. Sildenafil citrate can be effective in about 30-60 minutes after men take it, and it is more effective when taken on an empty stomach. Therefore, men can take it on an empty stomach and one hour before having sex, and then have sex afterwards. However, if you are taking nitrate drugs, you should not take it at the same time with this drug, because sildenafil citrate also has a certain antihypertensive effect, and taking the two at the same time may lead to an abnormal decrease in blood pressure, which may cause hypotension and other adverse reactions. The drug may cause adverse reactions such as facial edema, shock, weakness, pain, rash, tachycardia, palpitations (rapid heartbeat, often accompanied by panic), hypotension, and postural hypotension. The drug is contraindicated in women, people who are allergic to the product, children, people whose recent cardiovascular state does not allow them to have sex. The drug is a prescription drug and should be used in strict accordance with medical advice.