Jimmy, I would like to tell you that illicit drugs will harm your j-pouch, but really, it would not harm your j-pouch any more than it would harm the rest of your body. You can look up side effects of various recreational drugs as easy as the next guy, so I think you know about all that. My primary concern would be not about the drugs you know you are taking, but the fact that the dealers cut their drugs with all sorts of stuff, and THAT is where the real harm can take place. This is not about medication grade cocaine or medical marijuana, but street drugs with who-knows-what added in. In addition, even if the cutting agent is perfectly safe (most likely), you do not know the concentration of the cocaine, or whatever, that you are using. That is how overdose happens.
Realistically, it is like Russian Roulette. You are fine, until you are not. It is your choice whether that is an acceptable risk.
There are however, a number of people here and some evidence that marijuana does help with some symptoms of a dysfunctional pouch. But, I doubt it makes a good functioning pouch better.
Jan
