The main ingredient in both lomotil and Imodium (loperamide) act in pretty much the same way. They are opioid derivatives that work in the opiate receptor for effect on the intestines. This is the side effect of all opiates that is usually a bad thing: constipation. They lack the pain relieving and euphoric effect in therapeutic doses. Even in high doses, there is no opiate withdrawal syndrome with loperamide, but there may be with lomotil, especially after high dose, long term use. That said, after a certain level, there is no useful added effect, so high doses are just money down the drain, so to speak.
It is said that Imodium actually actively increases water absorption, but I am not 100% sure of that. It also is known to improve resting sphincter pressure, which is good if you have a night time leakage issue, bad if you tend to strain against tight sphincters.
Lomotil also has a small amount of atropine added to prevent abuse (such as taking huge doses in an effort to get high). If you are very sensitive to atropine, it could give you heart palpitations, and the "jitters." On the other hand, atropine is an antispasmodic. But, the amount is really too low to be useful in that respect.
One other thing is that Lomotil is still a schedule V narcotic in the U.S. (it would be a schedule II without the atropine). The abuse potential is practically nil, but present, since the diphenoxylate portion does cross the blood-brain barrier (not true of Imodium). Plus, it is prescription only, while Imodium is over the counter. Basically, Imodium is just the safer drug overall. It is possible to put yourself into a coma by overdosing with Lomotil.
Bottom line, they are both very good, and as Scott said, the one that works for you is the best one for you. They have both been around for many decades, so they are well tested.
Jan
