How Medications Affect Constipation
How Medications Affect Constipation
Joy Stepinski, MSN, RN-BC
October 11, 2026
In addition to poor diet and inadequate fluid intake, medications can negatively impact bowel health. Side effects may include abdominal pain, bloating, nausea, vomiting, and changes in bowel habits. While lifestyle factors can significantly improve bowel habits, medication-related effects are another important factor that is often overlooked.
One medication class commonly associated with constipation is opioids. These medications are prescribed to help manage severe pain. The Centers for Disease Control and Prevention describes opioids as “chemicals that interact with opioid receptors on nerve cells in the body and brain, and reduce the intensity of pain signals and feelings of pain” [1].
A Cochrane analysis found that for every 17 people treated with an opioid, approximately one additional person developed constipation, compared with those receiving a different treatment [2]. While this number does not seem large, constipation can be a frequent and sometimes persistent problem for people taking opioids. Constipation is one of the most common adverse effects of this drug class [3]. Symptoms may include harder stools, reduced bowel motility, increased straining, and a feeling of incomplete stool evacuation.
Beyond opioids, anticholinergic medication can also interfere with normal bowel function. These medications have numerous potential side effects – enough to fill an entire article! They work by blocking acetylcholine, an important chemical messenger in the body’s nervous system. In the gastrointestinal tract, this action can slow intestinal movement and contribute to constipation. Experiencing this effect may vary depending on factors such as age, comorbidities, and lifestyle [4].
A systematic review of 11 studies involving 211,921 patients found that nine studies totaling 207,795 participants reported an association between anticholinergic medication use and constipation [5]. These medications treat a range of conditions, including motion sickness, nausea, allergies, respiratory conditions, Parkinson’s disease, cardiac arrhythmias, gastrointestinal conditions, and bladder conditions.
Certain medications used to manage high blood pressure may likewise affect bowel habits. Calcium-channel blockers can relax smooth muscle in blood vessels and may reduce intestinal contractions, slowing the movement of stool [6]. Diuretics increase urine production by removing water and salt from the body. If fluid intake does not adequately replace these losses, dehydration may contribute to harder stools and constipation. Studies have also found a relationship between constipation and an increased risk of cardiovascular events.
Certain antidepressant medications, such as tricyclic antidepressants (TCAs), are another drug class that may cause constipation [7]. An example is amitriptyline. A meta-analysis comparing the adverse effects of TCAs and selective serotonin reuptake inhibitors (SSRIs) found that constipation was reported in 22% of people taking TCAs, compared with 11% of those taking SSRIs. Furthermore, one-third of patients who discontinued TCA therapy because of an adverse effect experienced dry mouth, constipation, or dizziness.
Although constipation is a frequent side effect of pharmaceutical drugs, it can also occur with dietary supplements. As we have discussed in previous articles, supplements are not without risks. Iron is a commonly used supplement to treat iron deficiency and iron-deficiency anemia. Gastrointestinal side effects are among the most commonly reported effects of oral iron. In a systematic review, constipation was reported in 12% of people taking ferrous sulfate across the 27 studies that highlighted constipation as an adverse effect [8].
In conclusion, constipation can be caused by a variety of factors, including medications and supplements. Medication-related constipation is an important side effect to recognize that may be overlooked. Understanding the potential side effects of your medication and any treatment is an essential part of being an informed healthcare consumer. If you have a concern about a medication affecting your bowel health, always consult your healthcare provider so that you can make an informed decision about future actions.
References:
Centers for Disease Control and Prevention. (2024, April 19). Commonly used terms. https://www.cdc.gov/overdose-prevention/glossary/
Els, C., Jackson, T. D., Kunyk, D., Lappi, V. G., Sonnenberg, B., Hagtvedt, R., ... & Straube, S. (2017). Adverse events associated with medium‐and long‐term use of opioids for chronic non‐cancer pain: an overview of Cochrane Reviews. Cochrane Database of Systematic Reviews, (10). https://doi.org/10.1002/14651858.CD012509.pub2
Norton, P. D., & Bharucha, A. E. (2016). Management of opioid-induced constipation. British Journal of Nursing, 25(10), S4 – S11. https://doi.org/10.12968/bjon.2016.25.10.S4
Bishara, D. (2023). Anticholinergic action is rarely a good thing. Therapeutic Advances in Psychopharmacology, 13. https://doi.org/10.1177/20451253231195264
Rodriguez-Ramallo, H., Baez-Gutierrez, N., Prado-Mel, E., Alfaro-Lara, E. R., Santos-Ramos, B., & Sánchez-Fidalgo, S. (2021). Association between anticholinergic burden and constipation: A systematic review. Healthcare, 9 (5), 581. https://doi.org/10.3390/healthcare9050581
Kume, T., & Mogi, M. (2025). The inseparable relationship between constipation and blood pressure. Hypertension Research, 48(5), 1687-1689.
Trindade, E., Menon, D., Topfer, L. A., & Coloma, C. (1998). Adverse effects associated with selective serotonin reuptake inhibitors and tricyclic antidepressants: a meta-analysis. CMAJ : Canadian Medical Association Journal = Journal de l'Association médicale canadienne, 159(10), 1245–1252. https://pmc.ncbi.nlm.nih.gov/articles/instance/1229819/pdf/cmaj_159_10_1245.pdf
Tolkien, Z., Stecher, L., Mander, A. P., Pereira, D. I., & Powell, J. J. (2015). Ferrous sulfate supplementation causes significant gastrointestinal side-effects in adults: a systematic review and meta-analysis. PloS One, 10(2), e0117383.https://doi.org/10.1371/journal.pone.0117383