Viagra (sildenafil citrate is a treatment for impotence that has become increasingly common as a recreational drug, particularly amongst gay men who want to counteract the impotence side-effect of ecstasy. Several studies have linked Viagra use to increased risk of unprotected sex and STIs, although is it unclear whether this is because Viagra enables men to have more partners or increases the length of sexual exposure. It is also possible that these men simply added Viagra to their risk-taking repertoire.

The most common side-effects of Viagra are headaches, facial flushing, indigestion, nasal congestion and transient disturbance of colour vision. In the clinical trials, 30% of participants reported a side-effect but only 2% stopped taking the drug due to side-effects.

Viagra should not be taken in conjunction with 'poppers' or nitrates (e.g. amyl nitrate) or with drugs used to treat angina. If nitrates and Viagra are taken together, blood pressure may fall to dangerously low levels.