If you have ulcerative colitis (UC), your doctor might suggest Pentasa as a treatment option for you. It’s a prescription drug used to do the following in adults:

  • Treat UC with a bit of activity.
  • induce remission of UC

You can take a capsule called Pentasa. Mesalamine is an active ingredient. An active ingredient is what makes a drug work. If you and your doctor agree it is safe and effective for you, you will most likely take it.

For more information about Pentasa, including details about its uses, see this in-depth article.

Like other drugs, Pentasa can cause mild to serious side effects. Continue reading to learn more.

Some people may experience side effects during treatment. Examples include:

These are just a few of the more common side effects reported by people who took Pentasa in studies.

Many of the side effects of Pentasa are mild. Mild side effects have been reported with this drug.

The side effects explained section is where you can learn more about this side effect.

These side effects should be temporary. Some may be easy to manage. If you have any symptoms that bother you, talk to your doctor or pharmacist. If your doctor recommends it, you should not stop taking it.

Pentasa may cause mild side effects other than the ones listed above. See the drug’s prescribing information for details.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Pentasa, visit MedWatch.

Many of the side effects of Pentasa are mild. It is possible that some serious side effects may occur.

There have been serious side effects with this drug.

If you develop serious side effects while taking the drug, call your doctor. If the side effects seem life threatening or you think you have a medical emergency, immediately call the emergency number.

The side effects explained section is where you can learn more about this side effect.
† An allergic reaction is possible after taking Pentasa. But this side effect wasn’t reported in studies.

Some of the side effects of Pentasa can be found here.

Hair loss

In rare cases, hair loss was reported as a side effect in studies of people taking Pentasa. But it’s not clear if Pentasa was the cause.

Ulcerative colitis, which Pentasa is used to treat, makes it difficult for your body to absorb vitamins and nutrients. And many factors, including nutritional deficiencies and stress, can cause hair loss.

What might help

Talk with your doctor or pharmacist if you’re concerned about hair loss with Pentasa. They can recommend over-the-counter (OTC) treatments. Eating a balanced diet with foods high in vitamins B12 and D, biotin, riboflavin, and iron may also help with hair loss. Examples of these foods include:

  • They have avocados.
  • There are beans.
  • The berries are large.
  • Eggs.
  • There are nuts and seeds.
  • They have oysters.
  • There is a vegetable called spinach.
  • sweet potatoes.


Constipation was reported as a side effect in Pentasa studies, but it was rare. Symptoms include:

  • Having hard stools.
  • Having less than three bowel movements a week.
  • straining during bowel movements.
  • Even after having a movement in the colon, I feel full.

What might help

You can usually manage constipation with OTC stool softeners or laxatives, such as:

Talk to your doctor or pharmacist before taking OTC medications. They will let you know if they are safe to take with them.

If you have any of the following symptoms, please let your doctor know.

Joint pain

Some people reported joint pain in Pentasa studies. But this side effect was not common. Joint pain caused by Pentasa is usually mild and goes away within a few days to weeks.

What might help

Mild joint pain can be relieved with OTC medications, such as ibuprofen (Advil, Motrin) or acetaminophen (Tylenol). Always check with your doctor or pharmacist before taking OTC drugs. They’ll let you know if they’re safe to take with Pentasa.

If your pain is not getting better, talk to your doctor. They can recommend other treatments.

Kidney damage

Kidney problems, including kidney damage, have been reported in people taking Pentasa or other drugs that contain mesalamine. Symptoms of kidney problems include:

What might help

Immediately let your doctor know if you have any symptoms of kidney problems. They’ll do lab tests to check how well your kidneys are working. Depending on the test results, they’ll determine whether Pentasa is safe for you.

Allergic reaction

Like most drugs, Pentasa can cause an allergic reaction in some people. But this side effect wasn’t reported in studies. Symptoms can be mild to serious and can include:

What might help

If you have a mild rash, call your doctor. They may suggest a treatment to help you. Examples include:

  • an antihistamine you take by mouth, such as Benadryl (diphenhydramine)
  • You apply a product to your skin.

If your doctor confirms you have an allergic reaction to Pentasa, they will decide if you should continue taking it.

If you have a severe allergic reaction, you should call the emergency number. These symptoms could be life threatening and need immediate medical care.

If your doctor confirms you have a serious allergic reaction to Pentasa, they may want you to switch to another treatment.

Keeping track of side effects

Take notes on any side effects you are having during your treatment. You can share this information with your doctor. This is helpful when you are starting to use a combination of treatments.

Side effect notes can include things.

  • When you had the side effect, what dose of the drug was taking?
  • How soon did you experience the side effect?
  • What are your symptoms?
  • How did it affect your daily activities?
  • What other drugs were you taking?
  • Other information is important to you.

Sharing your notes with your doctor will help them learn more about how Pentasa affects you. If needed, they can use this information to adjust your treatment plan.

Get answers to questions about the side effects of Pentasa.

Can Pentasa cause weight gain?

Weight gain was not reported as a side effect in Pentasa’s studies. But other medications used to treat ulcerative colitis (UC), such as prednisone and Remicade (infliximab), may cause weight gain.

It’s also possible that symptoms of UC may lead to weight gain. Symptoms of UC, such as fatigue (low energy) and a frequent need to use the bathroom, can make it difficult for people with this condition to exercise regularly.

Bloating is also a symptom of UC. With bloating, your belly fills with air and gas. It looks bigger than usual, and you may feel like you have gained weight.

If you are concerned about gaining weight with Pentasa, talk to your doctor.

Is anxiety a possible side effect of Pentasa?

It’s not likely. Anxiety was not reported as a side effect in Pentasa’s studies.

Difficulty falling or staying asleep, which can be a symptom of anxiety, was reported in Pentasa’s studies. But this side effect was not common.

It’s possible to have anxiety related to UC. According to a 2021 review of studies, people with UC are more likely to have anxiety and Depression. than people without this condition. This is especially true during active UC. People with UC may have anxiety around their symptoms or flare-ups.

Let your doctor or another healthcare professional know if you have mental health issues related to UC. They can help you find ways to manage your anxiety. If you need professional mental health services, they can help.

Is there a higher risk of side effects with the Pentasa 500-mg capsules compared with the 250-mg capsules?

Not really. The side effects of the 500milligram capsule should be the same as those of the 250milligram capsule.

“The UC’s daily dose of Pentasa is usually 1,000. You can take two 500-mg and four 250-mg capsule per dose.”

If you have trouble swallowing pills, taking several capsules in one dose may cause discomfort or nausea. In this case, the 500-mg capsules may be easier to take. (You can also check out this article for helpful tips on taking pills.)

If you have concerns about the side effects of Pentasa, talk to your doctor.

If you have certain medical conditions, it may not be right for you to use pentasa. This is a drug-condition interaction. Other factors may affect whether or not you should use Pentasa. Before starting Pentasa, you should talk to your doctor about your health history. The list has factors to consider.

Kidney problems. Pentasa can cause potentially serious kidney problems. If you already have kidney problems, Pentasa can make it worse. Your doctor will check your kidney function before you start Pentasa and then often throughout your treatment. If you develop kidney problems, they’ll likely have you stop taking Pentasa.

Allergic reaction. If you’ve had an allergic reaction to Pentasa or any of its ingredients, your doctor will likely not prescribe Pentasa for you. Ask them about other medications that might be better options.

Liver problems. Some people taking drugs containing mesalamine, the active ingredient in Pentasa, have reported liver failure. These people had a history of There are problems with the bile duct.. Let your doctor know if you’ve had There are problems with the bile duct. before you start taking Pentasa. They’ll determine if this medication is safe for you.

Serious skin reactions. Serious skin reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis, have been reported in people taking mesalamine. (This is the active ingredient in Pentasa.) Let your doctor know right away if you have any skin reactions while taking Pentasa. They’ll likely have you stop this medication if your skin reactions are serious.

Sun sensitivity. If you have certain skin conditions, such as eczema, Pentasa may cause your skin to be more sensitive to sunlight than usual. Avoid sun exposure or use sun protection when outdoors.

Kidney stones. Pentasa can cause There are stones on the kidneys.. Your risk is higher if you’ve had them in the past. Let your doctor know if you have a history of There are stones on the kidneys.. And be sure to drink plenty of water during your Pentasa treatment to reduce your risk of developing them.

Aspirin allergy. Pentasa is a kind of salicylate drug, like aspirin. You should not take Pentasa if you have an aspirin allergy.

Alcohol and Pentasa

There are no known interactions between Pentasa and alcohol. But drinking alcohol can cause ulcerative colitis symptoms to flare up. And alcohol can worsen certain Pentasa side effects, such as There is a throbbing head., dizziness, and nausea.

If you drink alcohol, you should talk to your doctor about how much you should consume.

Pregnancy and breastfeeding while taking Pentasa

There aren’t enough studies to know if Pentasa is safe to take during pregnancy. If you’re pregnant or planning to become pregnant, talk with your doctor before starting Pentasa treatment. They’ll let you know if this drug is safe for you.

Mesalamine, the active drug in Pentasa, passes into breast milk in small amounts. Pentasa may be safe to take while breastfeeding. But some children who are breastfed by people taking mesalamine had There is a lot of There is a lot of diarrhea... Talk with your doctor about your options for feeding your child during your Pentasa treatment. If you choose to breastfeed while taking Pentasa, be sure to monitor your child for There is a lot of There is a lot of diarrhea…

Many of the side effects of Pentasa are mild and go away in a few days or weeks. It is possible to have serious side effects from this drug. If you have questions about the side effects of Pentasa, it is important to talk with your doctor. Here are some questions you can ask.

  • Does my risk of side effects depend on the amount of Pentasa I take?
  • How do the side effects of Pentasa compare with those of Lialda (mesalamine)?
  • Is my risk of There is a lot of There is a lot of diarrhea.. higher when I first start treatment?
  • Is there any foods that increase my risk of side effects with Pentasa?

For advice from others living with an inflammatory bowel disease (IBD) such as ulcerative colitis, join the Bezzy IBD community. To get news on treatments and tips for managing your condition, sign up for Healthline’s IBD newsletter.

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.