Based on NIH | Can metformin cause constipation, and what steps can I take to manage this side effect?

Yes metformin can cause constipation in some people, although diarrhea, nausea, gas, and stomach upset are more common. ^[1] Constipation is listed among the gastrointestinal side effects reported with both immediate‑release and extended‑release metformin products. ^{[1] [2]} In clinical information for extended‑release tablets, constipation occurred in about 1% to 5% of users and was reported more often than with placebo. ^[2] Extended‑release tablets may also appear as a soft “ghost tablet” in stool, which looks like the pill shell and is not harmful. ^[3]

How often and why it happens

• How often: Digestive side effects are common with metformin when treatment starts and often lessen as your body adapts over a few weeks. ^[4] While diarrhea is more frequently reported, constipation also appears in safety summaries for various metformin formulations. ^{[2] [5] [6]}
• Why it happens: The exact mechanism behind metformin’s gut side effects isn’t fully understood, but proposed explanations include changes in intestinal hormones, bile salt handling, and microbiome shifts; these effects can vary widely between individuals. ^[7]

First steps to reduce constipation

• Take with meals: Taking metformin with food can reduce gastrointestinal side effects and is commonly recommended. ^[4]
• Start low and go slow: If you recently began metformin or increased the dose, asking your clinician about a slower titration may help symptoms settle. ^[8]
• Hydration and fiber: Aim for adequate fluids and gradual increases in fiber (whole grains, fruits, vegetables) to soften stool and support regularity; this general approach is widely recommended for constipation management. ^[9]
• Physical activity: Gentle, regular movement can help stimulate bowel function. ^[9]

When simple measures aren’t enough

If constipation persists despite routine measures, over‑the‑counter options may help while you continue metformin after discussing with your clinician or pharmacist to make sure they’re appropriate for you. ^[10]

• Stool softeners (docusate): Increase water in the stool to make it easier to pass, and generally have few side effects. ^[11]
• Osmotic laxatives (polyethylene glycol, e.g., MiraLAX): Draw water into the bowel to soften stool; can occasionally cause gas or bloating. ^[12]
• Stimulant laxatives (senna, bisacodyl): Help the bowel contract; typically used short‑term or as rescue if other options fail. ^[12] Overuse of laxatives can lead to dependence or side effects, so follow label directions and professional advice. ^[9]

Medication adjustments that may help

• Extended‑release (ER) formulation: Some people tolerate ER metformin better than immediate‑release for gastrointestinal symptoms, and ER labeling acknowledges different GI side‑effect profiles, including constipation. ^[2]
• Dose changes or brief pause: If side effects last more than a few weeks, come back later, or are very bothersome, clinicians may lower the dose or consider a short interruption. ^[4]
• Microbiome‑targeted strategies (early evidence): Small studies suggest that adding a gastrointestinal microbiome modulator may improve metformin tolerance, though this is not standard care and should be discussed with your clinician. ^[13]

Important safety notes

• Differentiate from serious issues: If you develop severe abdominal pain, persistent vomiting, blood in stool, or symptoms of dehydration, seek medical advice promptly. (General safety guidance for laxatives and constipation self‑care emphasizes not delaying care with red‑flag symptoms.) ^[9]
• Other causes: People with diabetes can have constipation for reasons other than medication, including autonomic nerve changes, so persistent symptoms may warrant evaluation. ^[14]

Practical plan you can discuss with your clinician

1. Take each metformin dose with a meal and maintain good hydration. ^[4]
2. If new on metformin or after a dose increase, allow 1–2 weeks to adapt; consider slower titration if symptoms are ongoing. ^[8]
3. Add fiber gradually and increase physical activity as tolerated. ^[9]
4. If needed, try an OTC softener (docusate) or osmotic laxative (polyethylene glycol); reserve stimulant laxatives for short‑term rescue. ^{[11] [12] [9]}
5. If constipation is still troublesome, ask about switching to extended‑release metformin or adjusting the dose. ^{[2] [4]}
6. Consider evaluation for other causes of constipation if symptoms persist, especially if long‑standing diabetes is present. ^[14]

With these steps, many people can continue metformin comfortably while maintaining its blood‑sugar benefits, since most GI side effects are mild and tend to improve with time and simple adjustments. ^{[8] [4]}