Mesalamine: what it treats, how to take it, side effects
Last updated September 3, 2026.
Mesalamine is an anti-inflammatory that works where it lands - it stops the body from producing a substance that causes inflammation, right in the lining of the colon. You may know it as Lialda, Apriso, Pentasa, or Delzicol. It is the backbone drug of ulcerative colitis, both for calming flares and for keeping them calm.
What does it treat?
Ulcerative colitis - the swelling and sores in the lining of the colon and rectum - both treating active disease and maintaining remission. The maintenance half matters as much as the flare half: staying on it when you feel fine is what keeps you feeling fine.
How do you take it?
Depends on the brand, and the brand matters: Lialda tablets once daily with food; Asacol HD tablets three times daily on an empty stomach; Apriso capsules once daily in the morning with or without food; Pentasa four times daily; Delzicol two to four times daily. Swallow everything whole - the coatings exist to deliver the drug to the colon, so no splitting, chewing, or crushing. Pentasa and Delzicol capsules can be opened onto applesauce or yogurt and swallowed without chewing. Drink plenty of fluids. Missed dose: take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: muscle or joint pain, back pain, nausea, vomiting, heartburn, burping, constipation, gas, itching, dizziness, runny nose with sneezing, sore throat, and congestion, hair loss, and decreased appetite.
- Serious - call your doctor immediately: rash, hives, itching, peeling, or blistering skin; mouth sores or blisters; fever or flu-like symptoms; swelling of the eyes, face, lips, tongue, mouth, or throat; swollen glands; difficulty breathing or swallowing; new or worsening cough, chest pain, or shortness of breath; black or tarry stools, bloody vomit, or coffee-ground vomit; swelling of any part of the body; and side or back pain - the kidney signal.
Who should not take it?
Anyone allergic to mesalamine or its cousins - balsalazide, olsalazine, sulfasalazine - or to salicylates like aspirin. Flag myocarditis or pericarditis history, eczema, kidney stones, and liver or kidney disease; the delayed-release tablets carry a gastrointestinal-blockage flag. If you become pregnant, call your doctor.
When is it an emergency?
Chest pain, trouble breathing, throat swelling, black stools, or bloody vomit is emergency care. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why does the brand of mesalamine matter so much?
Same drug, different delivery engineering: each brand's coating releases mesalamine at a different spot or pace in the gut, so dosing ranges from once daily (Lialda with food, Apriso in the morning) to four times daily (Pentasa) - and the empty-stomach rule applies to some brands but not others. MedlinePlus lists them separately. A pharmacy switch between brands is a prescriber conversation, not a like-for-like swap.
Why do I stay on mesalamine when I feel fine?
That is the point of it: it is both a flare treatment and a maintenance drug, and the maintenance half is what prevents the next flare. Ulcerative colitis relapses when the inflammation suppression lifts - feeling fine is the evidence the drug is working, not evidence you can stop. The quit decision belongs to your gastroenterologist, with a plan.
Why did my doctor mention my kidneys before prescribing it?
Mesalamine is cleared by the kidneys, and rare kidney inflammation is on its watch list - the signals are side or back pain, changed urination, and swelling. Kidney stones or kidney disease are before-you-start flags, and periodic kidney labs are part of long-term therapy. The drug is gentle for most people; the monitoring exists for the minority where it is not.
Why can't I take it if I am allergic to aspirin?
Mesalamine is chemically a salicylate - aspirin's family - so an aspirin or salicylate allergy can cross-react. The same goes for its drug cousins balsalazide, olsalazine, and sulfasalazine. This is why the allergy question on the intake form is specific, and why a new rash, hives, or facial swelling on the drug is a call-immediately event.
Why do I need to drink plenty of fluids on it?
Hydration protects the kidneys doing the clearing - and dehydration concentrates the drug where it is processed. MedlinePlus includes the instruction directly: drink plenty of fluids while taking mesalamine. It also helps with the constipation on the common-effects list. Simple, but it is part of the prescription.
What happens if I miss a dose of mesalamine?
Take it as soon as you remember, unless it is almost time for the next one - then skip it and never double up. Maintenance drugs work on consistency: one missed dose is a blip, a pattern of misses is a flare invitation. Anchoring it to breakfast or a phone alarm is what keeps the question rare.