[britta]

I work at 18F but am speaking about my experience here and experiences heard from coworkers, not officially on behalf of 18F.

Applying to 18F didn't require a drug test for me. The application process asks this question in the background check part (details at "security clearance" at the bottom of https://pages.18f.gov/joining-18f/how-to-apply/ for anyone curious), but answering yes to the "have you ever done federally-illegal drugs" question is not an automatic disqualification. It can be a disqualification depending on the details of the drug use.