First off, a little experimentation in high school isn't going to disqualify you from a clearance, so long as you've stopped and it's been at least 6 months since you've tried it.
But yes they do ask questions about drug use in the Standard Form 86 (Questionnaire for National Security Positions). It's section 23, starting on page 93.
https://www.opm.gov/forms/pdf_fill/sf86.pdfFor the record, I just had my periodic reinvestigation for my TS-SCI last year. And yes, they asked me.
So my advice: I would tell the truth to the recruiter -
but only if he asks. And if he does, make clear it was as you said, a stupid decision that you won't repeat. Then follow his advice throughout the rest of the enlistment process.
But as for the SF86 and the security clearance interview, yes, be up front and disclose everything, don't omit anything. You will be under oath. The investigator will interview your parents and your references, and then he will ask them for other people to ask about you. He or she may or may not uncover your drug use, but getting caught lying on the SF86 about anything is grounds for an automatic disqualification. Given how minor your "offense" was, it's not worth the risk.
HHH 95
LTC, US Army