soshy,I smoke and I can't say that it really "causes" an IBS-D episode ALL the time, but it certainly does stimulate a gut response more often than not.Interestingly, there was a time when that urge had to be met within seconds of the onset. Then, when I started taking the Caltrate, I could cope with the urge a lot better - meaning that I had a minute or so to get to the toilet, instead of seconds.Now, when I go out into the garage to have a cigarette (my wife and I have agreed not to smoke inside our new house), I can control the urge brought on by taking a drag so that at least I can finish the stick. So, smoking gives me a confirmation that the Caltrate is working. Of course, I don't need to smoke a cigarette just to verify to myself that the Caltrate is working, but it is a curious nuance to me.And, when I've taken an immodium and am done with whatever business I took it for, lighting up a cigarette back at home generally gets me out of that immodium constipation effect.None of this is an argument in favor of smoking - in fact, I am encouraged by all the responses from former smokers here because I'd like to quit myself.Nevertheless, in answer to your question: yes and no. Smoking does, I think, enhance the symptoms of IBS-D, but I don't think quitting will necessarily make those symptoms go away completely. And the amount that those symptoms will be reduced by quitting really depends on how severe your IBS is to begin with.For me, I can smoke and still manage my IBS reasonably. It'd be good to quit though.BJ