Anticholinergic/Antispasmodic Agents

Antispasmodics are drugs that inhibit smooth muscle contractions in the GI tract.

There are three major classes of antispasmodics:

  • anticholinergics,
  • direct smooth muscle relaxants,
  • and peppermint oil (to be discussed separately).


Anticholinergics reduce spasms or contractions in the intestine. This provides the potential to reduce abdominal pain and discomfort. The most common anticholinergics include hyoscyamine (Levsin®, NuLev®, Levbid®) and dicyclomine (Bentyl®). These can be taken daily or as needed. Each dose should be taken 30-60 minutes prior to a meal. Both drugs can be taken by mouth. Hyoscyamine is also available in a sublingual formulation. The sublingual form is placed under the tongue and allowed to dissolve there. Limited clinical studies suggest that these may improve pain (more specifically cramping) in people with IBS. Their efficacy for improving overall IBS symptoms has not yet been proven. As such, this makes them less attractive treatments for IBS.

Side effects of anticholinergics

The most common side effects include headaches, dry eyes and mouth, blurred vision, rash as well as mild sedation or drowsiness. Overall, these side effects are minimal, making them quite safe to use

Direct Smooth Muscle Relaxants 

Smooth muscle relaxants are not currently available for use in the United States. These drugs appear more effective for treating overall IBS symptoms than anticholinergics. The direct smooth muscle relaxants found to be effective include cimetropium, mebeverine, otilonium (available
in Mexico), pinaverium bromide, and trimebutine. Side effects with smooth muscle relaxants appear to be rare.

Peppermint Oil

Peppermint oil is generally considered an antispasmodic as it shares similar properties with
other medications. However, other traits make this particular agent unique. It causes smooth muscle relaxation by blocking calcium entry into intestinal smooth muscle cells. Calcium triggers muscle contraction, so the lack of calcium results in relaxing intestinal muscles. It also has anti-inflammatory, antigas, and anti-serotonergic properties. Serotonin is a chemical found in the gut that accelerates movement. Limiting the amount of serotonin in the gut may be more effective for people with IBS-D.

Recent studies have shown that it can be used to treat both overall symptoms and pain. This treatment may also be used either daily or as needed. Peppermint oil can be found in the form of teas, drops, gels, and capsules. There have not been any specific trials comparing one form to another. Side effects are uncommon but can include heartburn and nausea. These may be reduced by using a coated form. Coated pills minimize the activity of the peppermint oil in the stomach (IBgard®, Pepogest®).

Side Effects of Peppermint oil

Peppermint oil use can rarely cause skin rashes, headaches, or tremors. In clinical trials, these side effects do not occur more frequently in people taking peppermint oil than in those taking a placebo. A placebo is a pill or treatment with no active ingredients. 


Last modified on May 25, 2021

Taken from IFFGD Publication #168 Current Pharmacologic Treatments for Adults with Irritable Bowel Syndrome By: Darren M. Brenner, MD, Associate Professor of Medicine and Surgery, Northwestern University -Feinberg School of Medicine, Chicago, Illinois; Adapted from an article by: Tony Lembo, MD, Professor, of Medicine and Rebecca Rink MS, Beth Israel Deaconess Medical Center, Harvard Medical School, MA; Edited by: Lin Chang, M.D., Professor of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA

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