Carey,
Bentyl antagonizes acetylcholine at muscarinic receptors (anticholinergic), relaxing the smooth muscle in your gut and inhibiting painful (bradykinin- and histamine-induced) spasms. Bentyl has similar side effects to Benadryl (also an anticholinergic medication): headache, insomnia, heart palpitations, dry mouth, constipation, and urinary retention. Your pharmacist should be able to tell you all the medication interactions. Avoid other sedating medications like Percocet.
Dr. S (spouse of a Crohn's sufferer)