Medication-induced constipation or diarrhea is a common struggle faced by many, especially those with chronic conditions such as inflammatory bowel diseases as well as those with neuropathic pain, depression and anxiety. Here, we explain which medications can cause chronic constipation and how personalized drug therapy, vitamins and supplements can help alleviate these symptoms.

How medications slow down digestion and bowel movement

Many medications directly affect gut motility, which is the automatic contraction of the gastrointestinal muscles used by the body in order to move food, liquid, and eventually waste products throughout the digestive system. Changes to gut motility can affect the speed and ability with which the body is able to perform necessary natural digestive function, and can result in further concerns such as constipation. Normal gut motility is stimulated by a variety of signals from receptors on the muscles, triggered by serotonin and acetylcholine. Drugs that block these signals or the production of neurotransmitters or hormones that regulate the digestive system can cause chronic constipation. Commonly, people with chronic pain who take opioid painkillers need to take laxatives to combat this. Severe opioid-induced constipation requires other drugs that block opioid effects in the gut without affecting pain relief, such as methylnaltrexone (Relistor), naloxegol (Movantik), and naldemedine (Symproic). Lubiprostone (Amitiza) also helps increase fluid in the gut. However, these agents are not appropriate for people with constipation caused by non-opioid medications.

Medications that commonly cause constipation

For weight loss drugs and other medications, it is important to assess what type of constipation you have:

• Slow transit – Characterized by reduced frequency of bowel movements due to the drug’s action or the underlying condition, such as autonomic neuropathy in people with diabetes.
• Normal-transit – Characterized by an ordinary frequency of bowel movements, but an increased difficulty and/or pain when passing them. Typically related to inadequate hydration or dietary fibre intake
• IBS-type – Characterized by alternating bowel patterns and symptoms such as bloating.

In most cases, the risk of drug-induced complications rises with higher drug doses, longer treatment times, and the use of multiple medications and supplements, which lead to a gradual accumulation of the drug in your body. To better treat your drug-induced constipation, it is essential to understand how the drug works and how your body processes different medications. These insights can help guide safer and more effective treatment.

Pharmacogenetics is a science that reveals how your DNA can affect your response to medication and risk of side effects. Genetic-guided therapy helps to recover from anxiety and depression, reduce the risk of constipation or diarrhea for people with IBS, and optimize pain management.

An expert pharmacist can help you and your doctor better understand how to optimize your treatment and reduce the risk of medication-related side effects by switching to drugs better matched to your DNA. Careful selection of supplements can also reduce the severity of constipation.

How supplements can worsen or improve drug-induced constipation

In general, a healthy balance of vegetables, leafy greens, and high-fibre fruit are essential for gut health. However, people taking certain medications must avoid certain foods or supplements. For example, vitamin K supplements and leafy greens can affect the effectiveness of warfarin; grapefruit juice can affect the absorption and metabolism of many cholesterol drugs (statins) and other drugs. Fibre supplements, including Metamucil and psyllium, require adequate hydration, as insufficient water (or other fluid) intake can worsen constipation symptoms and affect drug absorption and metabolism as well.

Iron supplements are also known to increase the risk of constipation. Calcium, especially when combined with Vitamin D, can also reduce gut motility. Herbal and homeopathic supplements, such as St. John’s Wort, can significantly alter drug metabolism and affect the effectiveness and tolerability of many medications.

Supplements that can cause constipation

 Which remedies can help relieve constipation?

Standard first-line treatment of constipation typically involves the use of laxatives, which include a variety of substances and medications that relieve symptoms of constipation by promoting increased bowel movement. There are several different types of laxatives:

• Bulk-forming laxatives, such as the supplements containing psyllium and/or methylcellulose, trap water in the intestine using fiber which causes stool to increase in “bulk” and soften. This in turn stimulates the bowel muscles, causing them to contract and aid their passage.
• Osmotic laxatives, including magnesium, macrogol, and lactulose, draw water into the intestines to soften hard stool and improve transit, but they can alter electrolyte levels.
• Emollient laxatives, more commonly known as ‘Stool Softeners’ (e.g., docusate), reduce stool surface tension and are often combined with other laxatives.
• Stimulants, including coffee, bisacodyl and senna, stimulate intestinal muscles and increase water content.

Each type may provide only limited symptom relief, be ineffective for some individuals, or be associated with discomfort or side effects.

Senna

Herbal teas and supplements containing senna (Cassia species) are popular laxatives available without a prescription. It is generally safe, but excessive doses and prolonged use can cause liver problems. Senna works by activating the pro-inflammatory enzyme COX2. Because NSAIDs block COX2, senna will not work for people taking ibuprofen, celecoxib, and other medications in this class. Taking senna with NSAIDs can affect gut motility and potentially damage the GI tract, increasing the risk of adverse effects.

Coffee and caffeine: Do they help or worsen constipation?

Coffee is known to improve gut motility, but the effect is not driven by caffeine. The primary beneficial effects of coffee in regard to constipation are mediated by naturally occurring acetylcholine and flavonoids that stimulate muscarinic receptors in the gut. The decaffeinated coffee has the same effect on gut motility, but its effects are neutralized by medications with anticholinergic effects.

Drugs with anticholinergic effects that may block coffee’s GI stimulations include:

• Antispasmodic medications and supplements: atropine, mecamylamine, glycopyrrolate, vecuronium, succinylcholine
• Anxiety and depression: amitriptyline, paroxetine
• Antinausea: scopolamine
• Allergy: diphenhydramine
• Asthma: ipratropium, trospium
• Urge incontinence medications: oxybutynin, solifenacin, tolterodine

Additionally, genetic variations in asymmetric acetylcholinesterase (COLQ) and other genes that affect the activity of enzymes and receptors in the gut muscles and neurons can affect an individual’s GI response to coffee. It may be dangerous to increase coffee intake or use coffee enemas to treat constipation. High doses of caffeine can cause electrolyte imbalances (specifically sodium and chloride depletion), heart palpitations, anxiety, and dizziness, which can be fatal in people with certain genetic variants that affect heart rhythm (QT prolongation). To reduce your risk of GI and heart complications, consider switching to decaffeinated coffee and consult your pharmacist to determine whether any medications or supplements may interfere with its efficacy.

Supplement–medication interactions can be significant, and your pharmacist must carefully review the timing of your medications and supplements. Knowing how your DNA affects drug metabolism and response can help your pharmacist and doctor select appropriate medications and supplements to better manage your condition and reduce the risk of drug-induced constipation and other side effects.

Genes, vitamin B1 and drug-induced constipation

A recent study examined how the interplay among conditions, medications, and genetics affects stool frequency. It found that variants in the SLC35F3 and XPR1 genes, which are involved in thiamine transport and metabolism, influence the risk of drug-induced constipation in some individuals. The study also showed that higher dietary intake of thiamine (Vitamin B1) can increase stool frequency and alleviate drug-induced constipation in individuals with these genetic variants. Thiamine deficiency has been linked to GI disorders, particularly the so-called GI beriberi, characterized by impaired gut motility and digestion. Thiamine supplementation may help alleviate poor gut motility and IBS symptoms.

Lifestyle to reduce drug-induced constipation

A lack of physical activity can slow bowel movements. For people with chronic conditions and reduced mobility, yoga breathing exercises activate the diaphragm and abdominal muscles and can stimulate bowel movements.

Adequate hydration, especially for men with an enlarged prostate and women with urge incontinence, is essential. While you may avoid drinking fluids due to urge concerns, this can cause constipation, kidney stones, and significant health problems. Taking fibre supplements with low fluid intake will worsen GI symptoms.

Talk to a pharmacist or your doctor

If you have irregular bowel movements and regularly use suppositories or enemas, it is essential that you alert your healthcare providers about these issues. Seek medical help if you experience severe nausea and abdominal pain to assess for the risk of intestinal obstruction. Ultrasound imaging and/or colonoscopy may help rule out more serious health problems.

Your pharmacist can assess whether medication dose adjustments or switching to alternative drugs and supplements could help to improve GI motility. A pharmacogenetic test, such as Pillcheck, can help you and your healthcare providers better understand how your body processes different medications and suggest an alternative treatment plan, better matched to your DNA, to reduce the risk of medication side effects. The Pillcheck service includes a review of your medications, vitamins and supplements by an expert pharmacist.

While you can try using Vitamin B1, (decaf) coffee, senna and psyllium fibre, your DNA may hold the easier answer, which supplements are better suited for you.

Summary

• Certain medications and supplements may affect gastrointestinal motility. Prolonged use and higher doses increase the risk of severe constipation
• Irregular bowel movements may indicate a more severe condition and warrant timely assessment by a physician.
• A complex interaction between certain genetic variations and medications can indicate which supplements might help you to reduce the severity of GI symptoms.
• Careful review of your medications, supplements, and DNA profile can help a pharmacist optimize your therapy to reduce the severity of gastrointestinal symptoms and other side effects.

References

Díaz-Muñoz C et al., Genetic dissection of stool frequency implicates vitamin B1 metabolism and other actionable pathways in the modulation of gut motility Gut Published Online First: 20 January 2026.

Ismaiel A et al. Gastrointestinal adverse events associated with GLP-1 RA in non-diabetic patients with overweight or obesity: a systematic review and network meta-analysis. Int J Obes 49, 1946–1957 (2025).