Can Bentyl Cause Diarrhea? Understanding Dicyclomine's Effects on Bowel Function

October 9, 2025 •

4 min read

Dicyclomine, the active ingredient in Bentyl, is an antispasmodic prescribed for Irritable Bowel Syndrome (IBS). While it is designed to calm an overactive gut, many patients wonder: Can Bentyl cause diarrhea as an adverse effect?

Quick Summary

Bentyl (dicyclomine) primarily works by slowing gastrointestinal motility, and its most common gastrointestinal side effect is constipation. While less frequent, some patients report that Bentyl can worsen or even cause diarrhea, especially in certain conditions.

Key Points

Diarrhea is a possible side effect: While constipation is more common, a subset of patients may experience diarrhea or a worsening of existing diarrhea when taking Bentyl.
Bentyl primarily slows gut motility: As an anticholinergic, Bentyl is designed to relax intestinal muscles and decrease contractions, making constipation its most typical gastrointestinal effect.
Diarrhea can signal an underlying issue: In rare cases, persistent diarrhea while on Bentyl can indicate a more serious condition, such as an intestinal obstruction or severe ulcerative colitis, and requires immediate medical attention.
Individual responses vary: Patient experiences differ, with some finding Bentyl effective for cramps and associated diarrhea, while others report an opposite or unhelpful effect.
Drug interactions can cause diarrhea: Bentyl can interact with other medications, such as digoxin, potentially leading to toxicity with symptoms like persistent diarrhea.
Consult a doctor for symptom changes: Any new or worsened GI symptoms, including diarrhea, should be promptly discussed with a healthcare provider to ensure safety and adjust treatment if necessary.

Understanding Bentyl: An Anticholinergic Approach to Gut Health

Bentyl, the brand name for the generic drug dicyclomine, is a medication primarily used to treat the symptoms of Irritable Bowel Syndrome (IBS), such as painful cramping and spasms. It belongs to a class of drugs known as anticholinergics or antimuscarinics. By blocking the action of acetylcholine, a neurotransmitter that signals muscle contractions, dicyclomine relaxes the smooth muscles of the stomach and intestines. This mechanism is intended to reduce the painful muscle spasms that are characteristic of IBS.

The intended effect of Bentyl is to slow down an overactive gastrointestinal (GI) tract, which can provide significant relief for individuals experiencing cramping and diarrhea related to IBS. However, this same mechanism of action can sometimes lead to a variety of gastrointestinal side effects.

The Expected vs. Unexpected: Constipation and Diarrhea

Given its function as a GI motility-reducer, the most commonly reported gastrointestinal side effect of Bentyl is constipation. In fact, for patients with IBS-D (IBS with diarrhea), this effect can be a beneficial therapeutic outcome. However, a significant number of user reports and clinical data indicate that diarrhea can occur, and some individuals report that the medication actually exacerbates their symptoms.

Why Constipation is Common

Bentyl's anticholinergic action suppresses the natural peristaltic movement of the intestines. Peristalsis is the wave-like muscle contraction that moves food and waste through the digestive system. By slowing down this process, Bentyl can cause stool to move more sluggishly, leading to constipation. Some common side effects reported in clinical trials include dry mouth (33%) and nausea (14%), while constipation is a rare but noted side effect. For patients whose primary IBS symptoms are cramping and diarrhea, this constipating effect is often a welcome trade-off.

Why Diarrhea Can Still Happen

While counterintuitive, several scenarios can lead to or worsen diarrhea while taking Bentyl:

Paradoxical Reaction: Some individuals with IBS experience paradoxical reactions to medications. Instead of alleviating their diarrhea, the drug does not work for them and may even increase the frequency of loose stools. User-reported data on platforms like Drugs.com specifically mention diarrhea as a side effect for a subset of users.
Worsening Underlying Conditions: Medical warnings for dicyclomine note that diarrhea can be a symptom of an incomplete intestinal obstruction. In this case, treating the diarrhea with Bentyl would be harmful as it can worsen the obstruction. Additionally, for patients with ulcerative colitis, high doses of anticholinergics can suppress intestinal motility to a dangerous degree, potentially leading to toxic megacolon.
Drug Interactions: Certain drug combinations, such as dicyclomine with digoxin, can raise the risk of digoxin toxicity, which can manifest as persistent diarrhea, nausea, and vomiting. Patients must inform their doctor of all medications they are taking.

Potential Management of Gastrointestinal Side Effects

If you experience unwanted GI side effects while taking Bentyl, such as new or worsened diarrhea, it's crucial to consult your healthcare provider. They can help you determine the cause and adjust your treatment plan. Below are some general strategies that may help manage GI issues, though they should always be discussed with a doctor:

Review your medications: A healthcare professional should assess all your medications to check for potential interactions.
Dietary Adjustments: For constipation, increasing dietary fiber and fluid intake is often recommended. If diarrhea is the issue, a bland diet may be suggested. Certain foods and drinks, like spicy or fatty foods and alcohol, can worsen IBS symptoms and should be avoided.
Dosage Modification: Your doctor may decide to adjust your dose. For instance, if Bentyl causes excessive drowsiness or other side effects, your doctor may suggest taking the medication at bedtime.

Comparison of Bentyl with Other IBS Treatments

It is helpful to compare Bentyl with other IBS treatments to understand how different mechanisms can lead to different side effect profiles. The choice of medication depends heavily on the specific IBS symptoms a patient experiences.


Feature	Bentyl (Dicyclomine)	Ibsrela (Tenapanor)	Hyoscyamine (Levbid, etc.)
Drug Class	Anticholinergic, antispasmodic	Sodium/hydrogen exchanger 3 (NHE3) inhibitor	Anticholinergic, antispasmodic
Mechanism	Relaxes smooth muscles by blocking acetylcholine.	Prevents sodium absorption and helps soften stool; also works on nerves to relieve pain.	Relaxes smooth muscles by blocking acetylcholine.
Primary Use	Treat muscle spasms and cramping in general IBS.	Specifically for IBS with constipation (IBS-C).	Treat spasms in IBS and other GI conditions.
Common GI Side Effects	Dizziness, dry mouth, blurred vision, constipation.	Diarrhea, bloating, gas.	Dry mouth, constipation, drowsiness.
Targeted IBS Symptoms	Abdominal pain, cramps, spasms.	Constipation and abdominal pain.	Abdominal pain, spasms.

Conclusion

While Bentyl's primary pharmacological effect is to slow intestinal motility, making constipation a common side effect, it can cause or worsen diarrhea in some individuals. This often depends on individual physiological responses, drug interactions, and pre-existing conditions like an incomplete bowel obstruction or severe ulcerative colitis. For this reason, it is critical that patients report all gastrointestinal symptoms to their prescribing physician to ensure safe and effective treatment. Always discuss any changes in bowel habits with a healthcare professional to rule out more serious complications and determine the best course of action.

For more detailed information on dicyclomine, refer to the official FDA drug label for dicyclomine.

Frequently Asked Questions

Bentyl, or dicyclomine, is an anticholinergic medication that relaxes the smooth muscles of the gastrointestinal tract, which can slow down gut motility and most often leads to constipation.

While less common than constipation, some users have reported experiencing diarrhea or a worsening of existing diarrhea while taking Bentyl, suggesting that individual responses can vary significantly.

If you experience new or worsening diarrhea while on Bentyl, you should contact your doctor. They can determine if the medication is the cause, rule out more serious complications like an intestinal obstruction, and adjust your treatment plan.

Yes. In some cases, persistent diarrhea could be a symptom of an incomplete intestinal obstruction, and continuing to take Bentyl could be harmful. A doctor can help determine the true cause of your symptoms.

Yes. Bentyl can have drug interactions that cause adverse effects. For example, when taken with digoxin, it can increase digoxin levels and lead to toxicity, with symptoms including persistent diarrhea.

Bentyl is often prescribed for IBS symptoms like cramping, and its constipating effect can help manage diarrhea. However, some users do not experience this benefit and may even have their diarrhea worsened by the medication.

Bentyl is an antispasmodic for general IBS, while Ibsrela is specifically for IBS with constipation (IBS-C) and works differently. Bentyl's common GI side effect is constipation, while Ibsrela's is diarrhea.