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Asacol HD
Generic name: mesalamine (oral)
What is Asacol HD?
Asacol HD affects a substance in the body that causes inflammation, tissue damage, and diarrhea.
Asacol HD delayed-release 800mg tablets are used to treat moderately active ulcerative colitis in adults.
How should I take Asacol HD?
Take Asacol HD exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets.
This medicine can affect the results of certain medical tests. Tell any doctor who treats you that you are using Asacol HD.
Follow your doctor's instructions about taking this medicine with or without food. Some brands may need to be taken on an empty stomach, at least 1 hour before or 2 hours after a meal.
Drink plenty of liquids to help prevent kidney stones.
Swallow the tablet whole and do not crush, chew, or break it. Tell your doctor if you have trouble swallowing the tablet.
Tell your doctor if you find undissolved tablets in your stool.
Call your doctor if your ulcerative colitis symptoms do not improve, or if they get worse.
This medicine can affect the results of certain medical tests. Tell any doctor who treats you that you are using this medicine.
You may need frequent blood tests to check your blood cells or kidney function.
Your urine may become discolored reddish-brown when it comes in contact with surfaces or water treated with bleach (such as in a toilet). Tell your doctor if your urine is discolored before it leaves your body.
Store at room temperature away from moisture and heat.
Warnings
Stop using Asacol HD and call your doctor at once if you have severe stomach pain, stomach cramping, bloody diarrhea (may occur with fever, headache, and skin rash).
Before taking this medicine
You should not use Asacol HD if you are allergic to mesalamine, aspirin, sulfasalazine, or salicylates (such as Disalcid, Doans Pills, Dolobid, Kaopectate, Nuprin Backache, Pepto-Bismol, Tricosal, Trilisate, and others).
To make sure Asacol HD is safe for you, tell your doctor if you have ever had:
- a kidney stone or kidney disease;
- liver disease;
- a blockage in your stomach or intestines (such as pyloric stenosis);
- a skin condition such as eczema; or
- phenylketonuria (PKU).
Tell your doctor if you are pregnant or plan to become pregnant. It is not known whether mesalamine will harm an unborn baby. However, having untreated or uncontrolled ulcerative colitis during pregnancy may cause complications such as low birth weight or premature birth. The benefit of treating ulcerative colitis may outweigh any risks to the baby.
It may not be safe to breastfeed while using this medicine. Ask your doctor about any risk. If you are breastfeeding, tell your doctor if you notice diarrhea in the nursing baby.
Do not give this medicine to a child without medical advice. Some brands or forms of this medicine are not approved for use in anyone younger than 18 years old.
Asacol HD side effects
Get emergency medical help if you have signs of an allergic reaction to Asacol HD: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.
Stop using Asacol HD and call your doctor at once if you have:
- severe stomach pain, stomach cramping, bloody diarrhea;
- fever, headache, general ill feeling;
- rash, itching, eye redness;
- severe skin reaction - fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling;
- bloody or tarry stools, coughing up blood or vomit that looks like coffee grounds;
- low white blood cell counts - fever, chills, mouth sores, skin sores, sore throat, cough, feeling light-headed, trouble breathing;
- signs of a kidney stone - severe pain in your side and back, frequent need to urinate, foul-smelling urine, dark or cloudy urine;
- kidney problems - increased or decreased urination, swelling, weight gain; or
- liver problems - loss of appetite, upper stomach pain, tiredness, easy bruising or bleeding, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).
Low white blood cell counts may be more likely in older adults.
Common Asacol HD side effects may include:
- burping, constipation, nausea, vomiting, stomach pain, diarrhea, gas;
- dizziness;
- cold symptoms such as stuffy nose, sneezing, sore throat;
- back pain;
- headache;
- rash; or
- abnormal liver function tests.
This is not a complete list of side effects, and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
Dosing information
Usual Adult Dose for Ulcerative Colitis:
800 mg delayed release tablets: 1600 mg orally 3 times a dayDuration of therapy: 6 weeks.
What happens if I miss a dose?
Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.
What happens if I overdose?
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.
If you have a skin condition such as eczema, Asacol HD could make you sunburn more easily. Avoid sunlight or tanning beds. Wear protective clothing and use sunscreen (SPF 30 or higher) when you are outdoors.
What other drugs will affect Asacol HD?
Mesalamine can harm your kidneys, especially if you also use certain medicines for infections, cancer, osteoporosis, organ transplant rejection, bowel disorders, high blood pressure, or pain or arthritis (including Advil, Motrin, and Aleve).
Tell your doctor about all your other medicines, especially:
- azathioprine or 6-mercaptopurine.
- iron supplements.
- antacids; or
This list is not complete. Other drugs may interact with mesalamine, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.
Common questions about Asacol HD
How long does it take for mesalamine to work?
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Can I stop taking mesalamine?
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Content is provided for education and is not medical advice. See our medical disclaimer. Source page medically reviewed by Philip Thornton, DipPharm on October 1, 2026.