smoking cannabis will have no effect whatsoever on your sex drive or libido, don't worry about it; if anything, smoking some pot before sex makes it better... i don't have any first-hand experience with propranolol... it's a beta-blocker and it can lower your blood pressure so that may make it harder to achieve erection while on it... not sure if you take it every day? propranolol has a half-life of around 4-5 hours so if it was just a one-time thing, it will already have been well metabolized and out of your body by 48 hours out.