Aildenafil (methisosildenafil) is a synthetic drug that is a structural analog of sildenafil (Viagra). It was first reported in 2003. Like sildenafil, aildenafil is a phosphodiesterase type 5 inhibitor.

Aildenafil has been found as an adulterant in a variety of supplements which are sold as "natural" or "herbal" sexual enhancement products. The United States Food and Drug Administration has warned consumers that any sexual enhancement product that claims to work as well as prescription products is likely to contain such a contaminant.

Aildenafil is approved for use in China.