Depends. I've had strains that keep me high for as long as 3 hours. Sativas don't last as long in my experience. Then again, I have some sour diesel that is sativa dominant and it lasts forever. The high has stages: crazy and trippy, happy and swimmy, and mellow as it wears off.

Also, working out helps intensify the high. On the days I lift weights the high hits me a bit harder. Drinking a couple beers will increase the high. Only a couple though, like 3. Any more and you risk getting what I call "the spins" lol. Some strains mix better with alcohol than others too. I've heard smoking on an empty stomach gets you higher, and that makes sense because the blood would be circulating elsewhere, not in your stomach or intestines digesting something.