From the Guidelines

Cholestyramine (Questran) is a recommended initial therapy for managing chronic diarrhea, specifically bile acid diarrhea (BAD).

Cholestyramine is a bile acid sequestrant that can help reduce the frequency of watery stools in patients with BAD 1.
The Canadian Association of Gastroenterology suggests using cholestyramine as initial therapy for induction of clinical response in patients with BAD, although the evidence is rated as very-low-certainty 1.
Studies have shown that cholestyramine can be effective in reducing diarrhea symptoms in patients with BAD, with response rates ranging from 56% to 69.8% 1.
The dosage of cholestyramine can vary, but typical doses range from 2-12 g/d, and it can be given on-demand or as maintenance therapy at the lowest effective dose 1.
However, tolerability of cholestyramine can be poor, with common side effects including abdominal bloating and pain, dyspepsia, nausea/vomiting, and constipation, and some patients may prefer alternative treatments such as loperamide 1.

Cholestyramine should be considered for patients with chronic diarrhea who have risk factors for BAD, such as terminal ileal resection, cholecystectomy, or abdominal radiotherapy 1.
Testing for BAD using 75 selenium homocholic acid taurine (SeHCAT) or 7a-hydroxy-4-cholesten-3-one can help identify patients who may benefit from cholestyramine therapy 1.
Patients with extensive ileal Crohn’s disease or resection may not be suitable for cholestyramine therapy, and alternative antidiarrheal agents may be suggested instead 1.

From the Research

Cholestyramine is a bile acid sequestrant that is used to treat chronic diarrhea caused by bile acid malabsorption (BAM) 2, 3, 4, 5, 6
The medication works by binding to bile acids in the gut and preventing them from being reabsorbed, which can help to reduce the frequency and severity of diarrhea 4, 5
Studies have shown that cholestyramine is effective in treating chronic diarrhea in patients with BAM, with response rates ranging from 70% to 96% 4
Cholestyramine is generally considered to be the first-line treatment for bile acid diarrhea, and is often used as an empirical trial to rule out BAM as a cause of chronic diarrhea 4, 5

The diagnosis of BAM can be made using a variety of tests, including the SeHCAT test, which measures the level of bile acid malabsorption in the gut 2, 6
The SeHCAT test can help to identify patients who are likely to respond to treatment with cholestyramine, and can also be used to monitor the effectiveness of treatment 2, 6
In addition to cholestyramine, other medications such as colestipol and colesevelam may also be effective in treating BAM-associated diarrhea 4
Treatment with cholestyramine should be individualized and tailored to the specific needs of each patient, with doses ranging from 2-12 g/day 6

The clinical response to cholestyramine can vary depending on the underlying cause of the diarrhea and the severity of the BAM 2, 3
Studies have shown that patients with a positive SeHCAT test result are more likely to respond to treatment with cholestyramine, and are also more likely to require long-term maintenance therapy to control their symptoms 2
However, cholestyramine may also be effective in patients with chronic diarrhea who have a negative SeHCAT test result, suggesting that the medication may have other mechanisms of action beyond simply binding to bile acids 2, 3