Viagra sildenafil patent expiration date?

Patent expiry depends on country and which patent family you mean (composition, use, or formulation). Roughly:

- United States: Pfizer’s key sildenafil citrate (Viagra) patent for erectile dysfunction protection expired around 2012–2013, and generic sildenafil has been available in the U.S. since 2013.
- Worldwide: expiry dates vary by country and by which patent (there are multiple patents in play, including formulation and use patents). In many major markets the main protection ended in the early 2010s, but some secondary patents extended protection in certain jurisdictions to later years.

If you specify a country (and whether you mean the main ED-use patent, a formulation patent, or another patent family), I can give a more precise date and, if helpful, the patent numbers.