From my point of view, YES - taking chems has certainly lowered my brain capacity & physical strength.
Basically started taking trips & pot in '92, then started taking e's in '94. Introduced to speed in '95 and coke only last year (still have only tried it once). I haven't taken a trip since 95 (i think), but still smoke quite regularly (read every weekend). As to pilz 'n powder, I prolly indulge on average once/twice a month, only on weekends. I have just recently quit smoking (ciggies), but still feel quite tight in the lungs. This affects me because I like to surf big waves, and having small lungs, I need EVERY oxygen atom that I can get. I try to keep fit during the week, either by surfing, swimming or jogging, and take quite a few vitamins (multi, B, C, magnesium & Zinc). I just wish that there was something that I could take to keep my memory happening!
Timbo