What is Colesevelam?
Colesevelam, often known by its brand name Welchol, is a medication classified as a bile acid sequestrant [1.5.4]. It is primarily prescribed to lower LDL ("bad") cholesterol in adults and children over 10 with certain types of high cholesterol [1.9.3]. Additionally, it is approved to help improve glycemic control in adults with type 2 diabetes [1.5.5]. Colesevelam works by binding to bile acids in the intestine, preventing their reabsorption into the body [1.5.4]. This process forces the liver to use cholesterol to make more bile acids, which in turn lowers the amount of LDL cholesterol in the blood [1.5.4]. Because it is not absorbed into the bloodstream, its effects are localized to the gastrointestinal tract [1.5.2].
Primary Uses for Colesevelam:
- Primary Hyperlipidemia: To reduce elevated low-density lipoprotein cholesterol (LDL-C) [1.9.3].
- Type 2 Diabetes Mellitus: As an adjunctive therapy to improve glycemic control [1.5.5].
- Bile Acid Diarrhea (Off-Label): It is also used effectively to treat chronic diarrhea caused by bile acid malabsorption, a condition where excess bile acids irritate the large intestine [1.4.1, 1.8.2].
The Paradox: Can Colesevelam Cause Diarrhea?
While colesevelam is effective in treating specific forms of chronic diarrhea, it can also, paradoxically, cause diarrhea as a side effect [1.3.1]. Clinical studies list diarrhea as a "common" but less frequent side effect than constipation [1.2.2]. According to data, diarrhea occurs in 1% to 10% of patients taking the medication [1.2.2]. This places it in the less common category compared to constipation, which can affect up to 11% of users [1.9.4].
The exact mechanism for why a medication that binds bile acids (and thus firms stool) would cause diarrhea in some individuals is not fully understood. It may be related to individual differences in gut motility, the existing balance of the gut microbiome, or how the medication's bulking effect interacts with a person's specific digestive system. For some, the introduction of this non-absorbable polymer might irritate the gastrointestinal lining or alter fluid balance in the intestines, leading to looser stools.
Other Common Gastrointestinal Side Effects
Besides diarrhea, colesevelam is associated with a range of other GI symptoms. The most reported side effects include:
- Constipation: The most frequent side effect, sometimes severe enough to cause discomfort or lead to fecal impaction [1.2.1, 1.9.3].
- Indigestion (Dyspepsia) [1.9.4]
- Nausea [1.9.4]
- Bloating and Gas (Flatulence) [1.2.2]
- Abdominal Pain [1.2.2]
In rare cases, more severe issues like bowel obstruction have been reported, particularly in patients with pre-existing GI motility disorders [1.9.4].
Colesevelam vs. Other Bile Acid Sequestrants
Colesevelam is considered a second-generation bile acid sequestrant and is often compared to older drugs in the same class, like cholestyramine and colestipol.
| Feature | Colesevelam (Welchol) | Cholestyramine (Prevalite) |
|---|---|---|
| Formulation | Tablets or powder for suspension [1.6.5] | Powder for reconstitution [1.7.1] |
| Tolerability | Generally better tolerated with fewer GI side effects [1.7.2]. | Higher rates of GI side effects, particularly constipation and unpleasant taste [1.7.2]. |
| Common Side Effects | Constipation (up to 11%), dyspepsia, nausea [1.9.4]. | User-reported data shows diarrhea (22.0%), constipation (5.5%) [1.7.1]. |
| Drug Interactions | Fewer drug interactions compared to cholestyramine [1.7.3]. | Can significantly bind to and reduce the absorption of many other drugs [1.7.2]. |
Interestingly, user-reported side effect data from Drugs.com shows a higher percentage of patients reporting diarrhea with both drugs than clinical trials might suggest, with 27.2% for colesevelam and 22.0% for cholestyramine [1.7.1]. This highlights the variability of patient experiences.
Managing Side Effects
If you experience diarrhea or other gastrointestinal side effects while taking colesevelam, there are several strategies that may help:
- Start with a Low Dose: Healthcare providers often recommend starting with a lower dose and gradually increasing it over a couple of weeks to allow your system to adjust [1.6.2].
- Take with Food and Liquid: Always take colesevelam with a meal and a sufficient amount of liquid. This can help mitigate stomach upset [1.11.1].
- Adjust Timing of Other Medications: Colesevelam can interfere with the absorption of other drugs. It's crucial to take other medications at least 4 hours before or 4 hours after your colesevelam dose [1.6.1].
- Dietary Adjustments: For constipation, increasing fiber and water intake is recommended. For diarrhea, eating bland foods like crackers and broth may help [1.11.1, 1.11.3].
- Consult Your Doctor: Do not hesitate to speak with your healthcare provider. They may adjust your dose, suggest over-the-counter remedies for symptoms, or determine if colesevelam is the right medication for you [1.6.4]. Severe symptoms like intense stomach pain, vomiting, or signs of a bowel blockage require immediate medical attention [1.9.1].
Conclusion
So, can colesevelam cause diarrhea? Yes, while it is more commonly associated with constipation and is even used to treat bile acid diarrhea, it is listed as a potential side effect affecting 1-10% of users [1.2.2]. The experience of gastrointestinal side effects is highly individual. Colesevelam remains a valuable medication for managing high cholesterol and type 2 diabetes, and it is generally better tolerated than older drugs in its class [1.7.2]. Open communication with a healthcare provider is key to managing any side effects and ensuring the treatment is both effective and tolerable.
For more information from an authoritative source, you can visit the Mayo Clinic's page on Colesevelam. [1.2.1]
