Viagra is a medication primarily used to treat erectile dysfunction (ED) in men. It contains the active ingredient sildenafil citrate, which belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors. These medications work by increasing blood flow to the penis during sexual stimulation, which helps men achieve and maintain an erection suitable for sexual activity.

Viagra is not an aphrodisiac and does not increase sexual desire. It only works when there is sexual stimulation and does not have an effect on libido. It is generally prescribed for men who have difficulty achieving or maintaining an erection due to various underlying physical or psychological factors.

It's important to note that Viagra should be taken as prescribed by a healthcare provider and is not suitable for everyone. Common side effects may include headaches, flushing, indigestion, and nasal congestion. Serious side effects are rare but can include vision changes or sudden loss of vision, hearing loss, and priapism (a painful erection lasting more than four hours). Therefore, it's crucial to use Viagra under medical supervision and follow dosage instructions carefully.