What medications cause constipation?

If you got constipated after starting a medicine, you are not imagining it. The NHS lists a side effect of medicine among the common causes of constipation, and names opioid painkillers as the classic culprit: opioids slow the gut directly, which is why constipation is nearly universal on regular opioid use. The wider list from clinical references includes iron supplements, antacids containing calcium or aluminum, anticholinergic drugs for bladder and allergy, some antidepressants, some blood pressure medicines like verapamil, and anti-nausea drugs like ondansetron. The NIH notes that medicines and dietary supplements can make constipation worse, and adds a subtler one: simply changing your medicines can shift your bowel habits while your gut adjusts. What to do about it: first, the NHS is explicit that you should speak to the GP before you stop taking any prescribed medicine, because the fix is usually adjusting, not abandoning; second, the basics work harder when a drug is the cause, so fluids, fiber, and movement matter more, not less; third, for opioids specifically, ask about a laxative plan from the start rather than waiting for trouble; and fourth, mention the medication connection at your appointment, because switching families often solves it. Constipation with sudden bowel-habit change, pain, or tiredness is a get-checked combination.