How soon may I have unprotected sex after a depo shot?

You should stay protected for the first week, possibly two to be on the safe side.

And remember, the shot must be given every 12 weeks, not 3 months. There actually is a difference.

My OBGYN always told me anytime I started a new form of birth control, to use back up protection for 2 weeks... as J9 said "to be on the safe side"

Also, please remember that the shot does not protect you against STDs, only pregnancy.