We don’t know.

The manufacturer has collected data, called “stability data,” that show that the medication is safe and effective through the expiry date, provided the medication has been stored correctly. The manufacturer has no data on the safety or effectiveness of the medication after the expiry date.

There is no reason to think that PrEP medications instantly become ineffective on the expiry date, but there is no way to know how long they may remain effective after that. Studies conducted in the 1980s and early '90s showed that some medications remain effective for years after they have expired, but no study like that has looked specifically at Truvada, Descovy, or their generic alternatives.