Wow, there's no lack of high moral posturing on this thread is there!
"OMG you can't take coke in your 40s..." etc.
Give it a break. There's one thing (for some) to rightly question the OP's own situation in terms of overall frequency and intensity of usage; another entirely (for others) to generalise and pidgeon-hole recreational drugs like a bunch of ignorant old biddies. Talk about becoming your own parents!
Is recreational drug use in adulthood patently a bad thing? I'd argue otherwise. It's the fact that the OP got caught is the key issue, and how to manage that - and which only a smattering have bothered to provide constructive advice on.
My own example: I spent a significant proportion of recreational time in my late teens and early 20's 'using' (yawn...) cannabis, MDMA, acid, cocaine (in decreasing order) then went about my daily business successfully. I kept it proportionate because I came from a solid family background and required no secondary emotional outlet, other than what we youth simply did in the early 90s then.
Since then, I have occasionally dabbled but in terms of years rather than months or weeks, e.g. I went to a party last July (2013) and had a few spliffs and lines of coke along with beer and red wine. Sure, it was a heavy night but my wife (we're now 40 with two DDs) who doesn't partake but had plenty of booze, was a mess the next day so I looked after the kids, relatively happily. Then nothing until May this year when I took two ecstasy pills in a club with old friends (fantastic fun!) but haven't hankered after them since.
If some of you are this judgmental towards someone who is actively seeking your advice, then your own approach towards your own kids' experiences is questionable. I'm obviously not advocating recreational drug use in general, but teenagers will do what they do regardless and from experience, an absolutism approach is neither helpful, nor necessary.
I'm personally glad that I have first-hand experience of very occasional drug use in my late 30's/early 40s. In small doses it keeps me 'in the loop' and it can be harmless fun if that's your bag - like canoeing down a gorge or eating at Michelin Star restaurants can be fun.
Key words from all that: solid family background ;-)