Here's some useful information on certain types of drugs and what they give you.
Weed - 5% Armour.
Acid - 10% Armour.
PCP - 10% Armour.
Ecstasy - 10% Armour.
Heroin - 10% Armour.
Cocaine - 15% Armour.
Crack - 20% Armour.
Obviously you'll become addicted to certain types of drugs if you use it, for instance you'll become addicted to crack/heroin the first time using it.
The withdrawal effects show up after circa 5 minutes, they don't last long but will lower your health quite a bit.
This guide is only targeting illegal drugs, i'm not aware of the effects of medical drugs like vicodin. As you can see, crack is basicly the best drug on PR-RP despite the IC addiction.