I got the fun of dealing with both those issues.
Telling them I did drugs, there were quite a few arguments over a period of about a month, but we sat down and cleared it all up, and now they're fine with it. It was pretty hard to start with, and I didn't say through choice.
Telling them I was gay, I did through choice after I met my current girlfriend. Mother was cool with it straight away, so were my dad and my sister. Mum gets on well with my gf and we've had no problems.
Looking back, before I told them either of the things, I was least looking forward to telling them I was gay, because I didn't want to be seen as a disappointment. Drugs I thought were less of an issue.
Now, however, I can discuss my relationship with my mother or comment on attractive women and it's easy for me, whereas drugs I feel a little awkward with for some reason. I feel fine telling them about stupid things I've seen on shrooms, or randomness on E, but coming home high, I hate. Maybe it's to do with them seeing me in a different state of mind. Dunno.
Turns out my parents had guessed that I was on drugs AND gay long before I told them.