It varies.Some people find one more effective for them than the other. I think technically Imodium on a per milligram basis is a bit more potent, but I'm not sure about a per tablet basis as I don't know the milligrams per tablet off the top of my head.But that is an "on average" basis and any given human may find one works better for them than the other, and I have no way to predict for you what will happen.Imodium is over the counter because people really don't abuse it, and Lomotil has a small potential for addiction. To counter using Lomotil to get high they do have an antispasmodic added to it (which may be why some people do better on it as they respond to antispasmodics, but not all IBSers do). Antispasmodics like the add to Lomotil (and you can find in Bentyl and Levsin but those are also both prescription only in the USA) can cause dry mouth and reduced sweating so you may need to be more careful in the heat if you take Lomotil than if you take Imodium. With Lomotil the antispasmodic side effects are annoying enough that usually limits how many of them people can take at one time. Imodium may be better if you sometimes need more than others as you don't have to worry about the antispasmodic dose.Peppermint is an over the counter antispasmodic some use so if you seem to need that and you won't or can't get a prescription for a separate antispasmodic that is an option. Some people also like the Imodium Advanced which combines simethicone (which can break up larger gas bubbles to smaller ones) with the Imodium and find that combination works well for them.