Could a medication be behind your gut symptoms? A checklist

Timing is one of the best clues in any gut mystery. If your bloating, constipation or loose stools started within weeks of a new prescription, a dose change or a new supplement, your medicine cabinet deserves a closer look.

This checklist covers common medications linked to digestive side effects in research. It's meant to help you have a better conversation with your doctor or pharmacist, not to stop anything on your own.

Before you start: make a complete list

• Every prescription, with the dose and roughly when you started it
• Over-the-counter medicines, including antacids, allergy pills and pain relievers
• Supplements, including iron, calcium, magnesium and fiber products
• Any recent dose increases or switches to a different brand or form

Then compare those start dates with when your symptoms began. A match doesn't prove cause, but it's worth raising.

Medications linked to constipation

A study using a large general practice database compared 7,251 people with chronic constipation, 6,441 with constipation of unspecified duration and 7,103 controls. Several medication groups were linked to higher odds of chronic constipation (Talley et al., 2003). Check whether you take any of these:

• Opioid pain medicines (odds ratio 1.6)
• Antidepressants (odds ratio 1.9)
• Antihistamines (odds ratio 1.8)
• Antispasmodics (odds ratio 3.3)
• Anticonvulsants (odds ratio 2.8)
• Diuretics, or water pills (odds ratio 1.7)
• Aluminum-containing antacids (odds ratio 1.7)

An odds ratio above 1 means higher odds, and the bigger the number, the stronger the link. An odds ratio of 1.9 means close to twice the odds. This kind of study shows an association, not proof that a drug caused constipation in any one person.

Iron supplements

Iron is one of the most common supplement culprits. A meta-analysis of 43 trials with 6,831 adults found that ferrous sulfate, the standard form of oral iron, significantly increased gastrointestinal side effects, with an odds ratio of 2.32 compared with placebo (Tolkien et al., 2015).

If you need iron, don't stop it on your own. Low iron is also worth understanding in its own right, so ask your doctor about the cause, and whether a different dose, schedule or form could suit you better.

Metformin and GLP-1 medications

Metformin is widely prescribed for type 2 diabetes, but a sizable share of people can't tolerate it at adequate doses because of digestive side effects. Diarrhea and nausea are the most common, and flatulence, indigestion, vomiting and abdominal discomfort also occur (Bonnet and Scheen, 2017).

The same review describes strategies such as starting at a low dose and increasing slowly, or using an extended-release form (Bonnet and Scheen, 2017). These are adjustments to make with your prescriber.

GLP-1 medications also commonly cause digestive side effects. In pooled data from three large trials of semaglutide 2.4 mg for weight management, nausea affected 43.9% of participants versus 16.1% on placebo, and constipation affected 24.2% versus 11.1% (Wharton et al., 2022).

Most of these side effects were mild to moderate, temporary and most frequent during or shortly after dose increases. Only 4.3% of people taking semaglutide stopped because of them (Wharton et al., 2022).

Acid-reducing medications

Proton pump inhibitors (PPIs), such as omeprazole, lower stomach acid, and researchers have proposed that this could change the environment in the small intestine. A meta-analysis of 11 studies found higher odds of small intestinal bacterial overgrowth (SIBO) in PPI users, with a pooled odds ratio of 2.28. The link appeared only in studies that diagnosed SIBO with intestinal fluid cultures, not in those that used a glucose breath test (Lo and Chan, 2013).

That's a signal worth knowing, not a reason to stop a PPI. If you've taken one for years, it's reasonable to ask your doctor whether you still need it, and at what dose.

What to do with your checklist

1. Don't stop or change a prescription on your own. Some medications need to be tapered or replaced.
2. Book a medication review with your doctor or pharmacist, and bring your list and symptom timeline.
3. Ask specific questions. Could this be contributing to my symptoms? Is there a different dose, timing, form or alternative?
4. Change one thing at a time, so you can tell what helped.

When it's more than a side effect

Don't assume a medication explains everything. Contact your doctor promptly if you have blood in your stool or black stools, weight loss you can't explain, severe or worsening abdominal pain, or vomiting that won't stop. The same goes for new bloating most days, especially with early fullness, pelvic pain or urinary urgency.

Sources

1. Talley NJ, Jones M, Nuyts G, Dubois D. Risk factors for chronic constipation based on a general practice sample. Am J Gastroenterol. 2003;98(5):1107-11. PMID 12809835
2. Tolkien Z, Stecher L, Mander AP, Pereira DI, Powell JJ. Ferrous sulfate supplementation causes significant gastrointestinal side-effects in adults: a systematic review and meta-analysis. PLoS One. 2015;10(2):e0117383. PMID 25700159
3. Bonnet F, Scheen A. Understanding and overcoming metformin gastrointestinal intolerance. Diabetes Obes Metab. 2017;19(4):473-481. PMID 27987248
4. Wharton S, Calanna S, Davies M, et al. Gastrointestinal tolerability of once-weekly semaglutide 2.4 mg in adults with overweight or obesity, and the relationship between gastrointestinal adverse events and weight loss. Diabetes Obes Metab. 2022;24(1):94-105. PMID 34514682
5. Lo WK, Chan WW. Proton pump inhibitor use and the risk of small intestinal bacterial overgrowth: a meta-analysis. Clin Gastroenterol Hepatol. 2013;11(5):483-90. PMID 23270866

This article is for general information and isn't medical advice. Never stop or change a prescribed medication without talking to your healthcare provider or pharmacist.