I still recommend the oldest form of self-defence, practiced by our ancestors thousands of years ago...
Run like hell! And remember, you don't have to be able to run faster than the bad guys, just faster than the slowest of your mates

I'm going to second the sound advice Seige gave you - by "light drugs" I presume you mean the old hemp (whoever mentioned aerosols - they are well known for being one of the most dangerous "substances" you can abuse - a good warning, but not necessarily a good comparison!).
Anyway - I could just say "drugs are bad" but I doubt that'll pursuade you, so I'll just explain myself:
If I'm going to club in a rough area of with a bad reputation (and I try not to), I don't even drink, or at least limit it to one beer. That way my reactions or assessment of a situation aren't compromised, and chances are whether fight or flight (and I much prefer flight), I already have a significant upper hand. The same goes for walking around places you know to be frequented by the sort of people who did that to you. I advise you to do the same!
As Seige said, drugs/drink and violence are a lethal combo, because people just don't have the sense to realise the consequences of what they're doing, or that one kick to the head or stab to the body could kill.
Honestly, police or no, the best advice I can give you is if you want to do a few recreationals (is there really nothing else to do...?!), go to a mate's house and have a giggle at the TV, don't be wandering round the streets incapable to any degree, because trouble will find you, and whether it's a mugging or a car crash or whatever, you need your wits about you!
That's the lecture over - I hope you're feeling better now, these things really shake you up, don't they?!