I remember a few years back having a conversation with a downhiller who'd been warned by his race team manager that his dope habit may become a problem if he started racing internationally, as he intended to, and got drug tested.
Although marijuana is on the banned list, it's not exactly performance enhancing, but he thought the illusion of floaty high speed after a smoke was well worth the downside of actually going far slower than when he raced pure. He's essentially a highly skilled, very talented downhill racer who gets a much bigger buzz from racing with a slightly altered mind than he does from getting a better result.
This is the other side of doping. I call it attitude doping. Instead of altering your body to make it go faster, you alter your mind to change the whole experience of what you're doing. Most of us do it socially, by drinking alcohol. For better or worse, it changes the way you perceive things. And in most cases it's not illegal, or even frowned upon.
Riding a bike whilst your mind is altered is not something I would particularly recommend, but I'm certainly not going to pretend I haven't done it from time to time.
I love riding woodsy singletrack, fast, listening to my favourite music, even though it dulls my other fine-control senses. I love riding in the dark, often listening to music too: I suspect that's the nearest I get to racing downhill slightly stoned these days, in that I get the sensation of speed without the reality. I love riding after a couple of pints of cider, although I once ripped the sole straight off my shoe on a steep climb after succumbing to a third pint of anaesthetising Thatchers Traditional. And I'm not proud about the time I followed a kerb several times around Hyde Park trying to ride the fifteen miles home after a big bike brand launch party at a Westend club about twenty years ago.
Oddly, I remember those mind-altered rides more than the regular ones. I wonder if winning races on body-altering dope has that effect. I suspect it does when you get caught... a bit like winning a cross country race by taking a short cut then feeling guilty about it for the rest of your life. I know someone who did that too. His mind was altered at the time.