when I tried to join up tp go kill ol' Bin Laden and Hussien, I also was joining a division that required the highest security clearances there was. I wasn't exactly honest about my youthful indiscretions, and they found out stuff about me I couldnt believe. Youd be amazing what FBI and CIA bg checks can bring up... Anyway thier biggest issue with me was that I had lied, kinda a no no for top secret clearance. I was told I probably would have been accepted if I had been honest. I was not accepted, and when I asked if I could join as regular enlisted, at that point they also told me no.
In my very humble opinion, I would say be honest to a degree. Todays military understands drug use in America, and has a bit of leniency for "experimentation". If you were in a hospital, and they "knew" you were shrooming, and if there was bloodwork done, theres a paper trail somewhere, whether you can find it or not.
Good luck, and I expect you to bring me 10 NATZI scalps!