Viagra is a legal prescription drug used to treat erectile dysfunction, containing sildenafil citrate. It is legal in many countries, including the US and most European countries, but can only be obtained with a valid prescription from a licensed healthcare provider due to potential risks and side effects. Online pharmacies claiming to sell Viagra without a prescription are illegal and may sell counterfeit or expired drugs. In the US, selling or distributing Viagra without a prescription is illegal and can result in fines and imprisonment. Different countries have different laws regarding the importation of Viagra for personal use while traveling internationally. Common side effects of Viagra include headaches, flushing, and upset stomach, while more serious side effects may occur. Viagra should not be taken by people taking nitrates for chest pain or guanylate cyclase stimulators for pulmonary hypertension, women, or children under 18 years of age.