I'm no expert on kids and drugs. But I've got some ideas. Firstly don't lie to them. Tell them that "insert currently trendy drug here" is the most dangerous drug ever, and they know you are lying. Even if its true. Tell them about your drug use. Don't gloss it. If there is stuff you regret, tell them. If there is stuff that was fun, tell them.
I'm not very adventurous with drugs, but I know people who have used dope, ecstasy, speed, heroin, and lots of alcohol. None of the ones I know have suffered much as a result. But my family has a tendency towards psychosis - so I tell my son that he might think twice about smoking dope - the consequences might not be pretty.