This information is for people who have irritable bowel syndrome. It tells you about antidepressants, a treatment used for irritable bowel syndrome. It is based on the best and most up-to-date research.
Do they work?
Yes. Antidepressants may help some people with irritable bowel syndrome (IBS).
What are they?
Antidepressants are medicines that are normally used to treat depression. They affect chemicals called neurotransmitters, which help carry messages between brain cells. Doctors also use antidepressants to treat pain and diarrhoea caused by IBS. You might be given an antidepressant if other treatments haven't helped you.
Doctors prescribe antidepressants for IBS at a lower dose than for depression, so there may be fewer side effects.
Antidepressants usually take a while to start working, so you might not feel the benefits of treatment for two or three weeks.
You need to take antidepressants every day, and not just when your symptoms flare up. So your doctor will probably prescribe antidepressants only if you have bad symptoms most of the time.
Most research in IBS has been ona group of antidepressants called tricycylics. Your doctor may suggest trying one of these drugs first. Tricyclic antidepressants (with their brand names) include:
There hasn't been quite as much research on the antidepressants called selective serotonin reuptake inhibitors (SSRIs). SSRIs include:
How can they help?
Antidepressants help some people with IBS.   In studies, about 6 in 10 people found their symptoms of IBS improved when they took an antidepressant. This compared with about 4 in 10 people who improved after taking a dummy treatment (a placebo).
There's been more research on a group of antidepressants called tricyclics. There are fewer studies on another group of antidepressants called SSRIs. However, the research so far suggests that tricyclics and SSRIs work equally well for people with IBS. 
How do they work?
Doctors aren't sure how antidepressants help people with IBS. Antidepressants help to relieve some kinds of nerve pain, so it's possible that they could also help with pain caused by IBS.
Another theory is that antidepressants work by treating underlying depression or anxiety. However, in several studies, the improvement in people's IBS wasn't connected to improvements in their mood. In one study, antidepressants worked best for people who weren't depressed. So, it might be that antidepressants work by helping with pain somehow, rather than by improving your mood.
Can they be harmful?
All antidepressants can have side effects. In studies looking at people with IBS, about 2 in 10 people got some kind of side effect, but none of the problems were serious.  The most common side effects were drowsiness and dizziness.