This information is for people who have irritable bowel syndrome. It tells you about anti-spasmodic drugs, treatments used for irritable bowel syndrome. It is based on the best and most up-to-date research.
Do they work?
Probably. Anti-spasmodic drugs can help some people with the pain and other symptoms caused by irritable bowel syndrome (IBS).
What are they?
Anti-spasmodic drugs relax the wall of your bowels. They include (with brand names):
You can get these drugs on prescription from your doctor. You can also buy several of them yourself from a pharmacy. Brands you can buy yourself include Colofac IBS and Buscopan IBS.
You can also get some of these medicines combined with a fibre supplement. You can get mebeverine as Fybogel mebeverine. It comes in a sachet which you mix with water.
Peppermint oil, a herbal treatment from the peppermint plant, also has an anti-spasmodic effect.
Anti-spasmodic drugs all work in slightly different ways. If one doesn't work well for you, it might be worth trying a different one. People often take anti-spasmodic drugs for a week or so at a time to control symptoms when they flare up. It's better to take these tablets when your symptoms get bad than to take them every day.
How can they help?
Anti-spasmodic drugs can help with irritable bowel syndrome, especially if your main symptom is pain.  You may also find that some of your other symptoms improve too.
One summary of the research found that about 6 in 10 people improved if they took anti-spasmodic drugs, compared with 4 in 10 people who took a placebo.  However, the better quality studies were less likely to find a benefit, which makes it harder to trust the results.
A second summary of research found that most of the anti-spasmodic drugs it looked at were better than a placebo at reducing symptoms, but - as with the previous summary - better quality studies were less likely to find a benefit. 
How do they work?
The muscles in the wall of your bowels can be overactive if you have irritable bowel syndrome. You may get spasms that cause pain and discomfort. Spasms are sudden, strong muscle contractions. Wind or stools may get trapped in your bowels. This can make you feel bloated.
Anti-spasmodic drugs work by relaxing the muscles of your bowels. This stops you having spasms. So you should feel less pain and be less bloated.