Can oxybutynin cause diarrhea? Exploring the Side Effects

October 10, 2025 •

4 min read

Affecting as many as 30% of men and 40% of women in the U.S., overactive bladder (OAB) is often treated with medications like oxybutynin [1.7.2, 1.7.3]. While effective, patients often ask: can oxybutynin cause diarrhea among its side effects?

Quick Summary

Oxybutynin is a medication for overactive bladder. Though more known for causing constipation, diarrhea is also a recognized side effect, affecting between 1% and 9% of users depending on the formulation [1.2.2, 1.4.1].

Key Points

Diarrhea is a Side Effect: While constipation is more common, oxybutynin can cause diarrhea in 1% to 10% of users [1.2.2].
Anticholinergic Action: Oxybutynin works by blocking acetylcholine, which relaxes the bladder muscle but can also affect other body systems like the GI tract [1.2.1, 1.4.3].
Dry Mouth is Most Common: The most frequent side effect of oxybutynin is dry mouth, followed by constipation and dizziness [1.2.7, 1.3.1].
Formulation Matters: Extended-release (ER) versions of oxybutynin may cause fewer side effects, including constipation and blurry vision, compared to immediate-release (IR) versions [1.5.3, 1.4.1].
Management is Key: Side effects like diarrhea and dry mouth can often be managed with simple measures like staying hydrated and using sugar-free gum [1.5.2].
Consult a Doctor: Persistent or severe side effects, including diarrhea lasting more than two days, should be discussed with a healthcare provider [1.2.8].
Alternative Medications Exist: If side effects are intolerable, other OAB medications like tolterodine may be an option as they are sometimes better tolerated [1.6.1].

Understanding Oxybutynin

Oxybutynin is an anticholinergic and antispasmodic medication primarily prescribed to treat the symptoms of overactive bladder (OAB) [1.2.1]. OAB is a condition characterized by a sudden, urgent need to urinate, frequent urination, and sometimes urge incontinence [1.7.2]. Oxybutynin works through a dual mechanism: it blocks the action of acetylcholine, a neurotransmitter that signals bladder muscles to contract, and it also directly relaxes the bladder's detrusor muscle [1.2.1, 1.4.3]. This combined action helps to increase the bladder's capacity and reduce the uncomfortable and often disruptive symptoms of OAB [1.4.3]. It is available in various forms, including immediate-release (IR) tablets, extended-release (ER) tablets, a transdermal patch, and gel [1.5.3, 1.6.2].

The Anticholinergic Effect and the GI Tract

The primary mechanism of oxybutynin is its anticholinergic effect, which is not selective to the bladder [1.4.4]. Acetylcholine receptors are present throughout the body, including in the salivary glands and the gastrointestinal (GI) tract. By blocking these receptors, oxybutynin slows down involuntary muscle movements. In the GI tract, this action typically leads to decreased motility, which is why constipation is one of the most frequently reported side effects, affecting up to 15% of users [1.2.2, 1.4.4].

Can Oxybutynin Cause Diarrhea?

While it seems counterintuitive for a medication that primarily causes constipation, diarrhea is a recognized side effect of oxybutynin [1.2.2, 1.2.3]. Multiple medical sources list diarrhea as a possible adverse reaction [1.2.1, 1.2.4, 1.2.5]. The incidence of diarrhea is generally lower than that of constipation. Reports show that diarrhea can occur in 1% to 10% of patients, with some studies on the extended-release formulation noting an incidence between 7% and 9% [1.2.2, 1.4.1].

The exact mechanism by which an anticholinergic drug might cause diarrhea isn't perfectly clear, but it could be related to complex changes in gut motility or individual patient responses. In rare cases, severe diarrhea or runny stools after meals could be a sign of a serious condition called pseudo-obstruction, where hardened stool becomes impacted and only liquid stool can pass around it. This requires immediate medical attention [1.2.8].

Other Common and Serious Side Effects

Beyond constipation and diarrhea, oxybutynin has a range of potential side effects due to its systemic anticholinergic action. The most common is dry mouth, which can affect up to 72% of people taking the medication [1.2.2, 1.2.7]. Other common side effects include:

Dizziness and drowsiness [1.3.1]
Blurred vision and dry eyes [1.2.4, 1.5.2]
Headache [1.2.1]
Nausea [1.2.2]
Decreased sweating, which can lead to overheating or heat stroke in hot environments [1.3.2]

Serious but rarer side effects can include confusion, hallucinations (especially in the elderly), difficulty urinating, rapid heartbeat, and severe allergic reactions like swelling of the face, lips, or tongue [1.3.1, 1.3.3].

Comparison with Other OAB Medications

When considering OAB treatments, it's helpful to compare oxybutynin to other options, such as tolterodine (Detrol).


Feature	Oxybutynin	Tolterodine (Detrol)
Primary Mechanism	Anticholinergic, antispasmodic [1.2.1]	Anticholinergic, more selective for the bladder than salivary glands [1.6.3]
Common Side Effects	Dry mouth (very common), constipation, dizziness, drowsiness, diarrhea [1.2.2, 1.3.1]	Dry mouth (less than oxybutynin IR), constipation, headache, dizziness [1.6.1, 1.6.5]
Efficacy	Some studies suggest it is more effective at reducing incontinence episodes [1.6.1, 1.6.4]	Efficacy is clinically similar to oxybutynin [1.6.1]
Tolerability	Higher incidence of dry mouth and side effects often leads to discontinuation [1.6.1, 1.6.3]	Generally better tolerated with fewer withdrawals due to side effects [1.6.1]
Formulations	Oral (IR, ER), transdermal patch, gel [1.6.5]	Oral (IR, ER) [1.6.5]

Managing Oxybutynin Side Effects

If you experience diarrhea while taking oxybutynin, it's important to stay hydrated by drinking plenty of fluids like water [1.5.2]. Do not take any other medications to treat the diarrhea without first speaking to a doctor or pharmacist [1.5.2]. If the diarrhea is severe or lasts for more than a couple of days, you should contact your healthcare provider [1.2.8].

For other common side effects:

Dry Mouth: Chewing sugar-free gum, sucking on sugar-free candies, and taking regular sips of water can help stimulate saliva production [1.5.1].
Constipation: Increase fiber in your diet, drink plenty of water, and try to exercise regularly [1.5.2].
Dizziness/Drowsiness: Avoid driving or operating heavy machinery until you know how the medication affects you. Alcohol can worsen these effects and should be avoided [1.5.1, 1.5.4].

Sometimes, a healthcare provider might suggest switching from an immediate-release to an extended-release formulation, as ER tablets can have fewer side effects [1.5.3].

Conclusion

So, can oxybutynin cause diarrhea? Yes, while less common than constipation, diarrhea is a documented side effect of oxybutynin. As an anticholinergic medication, its effects on the gastrointestinal system can vary among individuals. Most side effects, including dry mouth and constipation, are more prevalent. If you experience persistent or bothersome side effects from oxybutynin, including diarrhea, it is crucial to consult your healthcare provider. They can help manage the side effects or explore alternative treatments for your overactive bladder to find a solution that works best for you.

For more information on OAB and its treatments, you can visit the Urology Care Foundation.

Frequently Asked Questions

Diarrhea is not one of the most common side effects, but it is a recognized possibility, affecting between 1% and 10% of people who take it. Dry mouth and constipation are much more common [1.2.2, 1.2.7].

While its primary anticholinergic effect slows the gut, which typically leads to constipation, medications can have complex and sometimes paradoxical effects on the gastrointestinal system depending on the individual. In rare instances, severe diarrhea could also be a sign of stool impaction [1.2.8].

You should drink plenty of fluids to avoid dehydration. Do not use over-the-counter anti-diarrhea medicine without consulting a doctor first. If the diarrhea persists for more than a day or two or is severe, contact your healthcare provider [1.5.2, 1.2.8].

The most common side effects are dry mouth, constipation, dizziness, drowsiness, headache, and blurred vision [1.2.2, 1.3.1].

Yes, transdermal forms of oxybutynin, like the patch or gel, deliver the medication steadily and avoid the initial processing by the liver. This generally results in fewer systemic side effects like dry mouth and constipation compared to the oral tablets [1.2.1, 1.3.1].

It is recommended to avoid alcohol, as it can worsen side effects like dizziness and drowsiness [1.3.3, 1.5.1].

You should contact your doctor if any side effects are severe, don't go away, or are very bothersome. Seek immediate medical attention for signs of a serious reaction, such as swelling of the face or throat, difficulty breathing, or severe confusion or hallucinations [1.3.3, 1.5.3].