I ran my first marathon in May, 1972 in 4:34:30. It was much slower than even my most conservative expectations. I'd thought running for an hour each day and for about two hours once a week would have me in decent shape.
When I looked at my diary I saw that I'd really only had three weeks when I had actually done that. I skipped a LOT of days. So I quit doing that and got to 50 to 70 a week through the summer and autumn. In November '72 I ran an hour five minutes faster.
If the OP and probably you knew me then I imagine so much improvement in so little time would make you suspect me. That wouldn't have bothered me. I think I'd have laughed about it. But a great thing about this sport is when some who's dabbled in it and never showed any ability gets really serious and gets performances s/he could once have only fantasized about. It's sad if such people aren't given all the credit they deserve.
I, at 71, have no idea where I'd get the drugs you're talking about. But I suspect that many of the people who do know and do take them are not doing it for improved running but to be able to do things they can't anymore because of age. Better running is a by product, though I may be totally wrong here.