Skip to main content


Aminosalicylates are a group of medicines used to treat inflammation of the gut that are used to treat and prevent flare-ups of ulcerative colitis.

Continue reading below

What are aminosalicylates?

Aminosalicylates are a group of medicines that can help to control the symptoms of some inflammatory bowel (gut) diseases, and treat ulcerative colitis and Crohn's disease. See the separate leaflets called Inflammatory Bowel Disease, Ulcerative Colitis and Crohn's Disease.

They include balsalazide, mesalazine, olsalazine and sulfasalazine, and come in various different brand names. They also come in a variety of different forms:

  • Tablets or liquid to be taken by mouth.

  • Liquid or foam enemas.

  • Suppositories to be inserted into the back passage (rectum).

The type of aminosalicylate that you are prescribed (for example, tablet or enema) depends upon where the inflammation is in your gut.

Aminosalicylates are mainly used:

  • To help keep people with ulcerative colitis in remission. That is, to keep symptoms away and prevent flare-ups.

  • To treat flare-ups of ulcerative colitis.

Aminosalicylates are sometimes used to treat flare-ups of Crohn's disease. But it is not common to use them for this, as most experts now think that they are not as effective as other treatments for Crohn's disease.

There is also some evidence that if you have ulcerative colitis then taking an aminosalicylate on a long-term basis can significantly reduce your risk of developing bowel cancer.

Aminosalicylates are also used to treat some forms of arthritis. However, the rest of this leaflet is mainly about their use in inflammatory bowel diseases, in particular ulcerative colitis.

How do aminosalicylates work?

The precise way these medicines work is not fully understood. It is thought they work on the cells lining the gut to change the way the cells release certain chemicals including cytokines. These chemicals can contribute to making the gut inflamed, and may be a factor in causing the symptoms of inflammatory bowel diseases.

Are aminosalicylates immunosuppressants?

Aminosalicylates are medicines that help to reduce inflammation. Inflammation helps damaged tissue to heal. However prolonged or excessive inflammation can cause bad effects such as pain, swelling, bruising or redness, and can cause damage to parts of the body in different health conditions, such as the bowel in Crohn's disease.

Aminosalicylates do not affect the body's defence (immune) system and so are not immunosuppressants.

Continue reading below

Are there different types of aminosalicylates?

There are quite a few available. The one that is best for you will depend upon where the inflammation is in your gut. All aminosalicylate medicines contain the active ingredient called 5-aminosalicylic acid (5-ASA). However:


Mesalazine comes in six different brand names: Asacol®, Ipocol®, Octasa®, Mezavant®, Pentasa®, Salofalk®. The way the manufacturers make each of these is a little different:

  • Asacol®, Ipocol®, Mesren® and Salofalk® each have a special coating which dissolves to release the active ingredient (5-ASA) at a certain pH (acidity) within the gut.

  • Each Pentasa® tablet is made up of tiny granules and the active ingredient is gradually released over the length of the gut.

  • Mezavant® tablets have a special hard centre that contains 5-ASA and they have a special coating.

This means they release 5-ASA all along the colon (large intestine).

Olsalazine and balsalazide

These have a special chemical bond in the formulation, which bonds the active ingredient. The bond is broken to release the active ingredient by the natural germs (bacteria) that live in the colon.

Sulfasalazine (Salazopyrin®)

This has an additional molecule attached called sulfapyridine. Some people may not be able to take medicines with sulfapyridine included - see below for details.

The small differences in how these medicines are made, and how you take (or use) them, can be important because inflammatory bowel conditions can affect different parts of the gut. To treat your symptoms effectively, your doctor may prescribe a particular form of medication. For example:

  • If your condition affects the back passage (rectum) only, you may be prescribed an aminosalicylate suppository or enema.

  • If your gut is affected higher up, you may be prescribed an aminosalicylate tablet:

  • Mezavant®, Dipentum® and Colazide® target the colon.

  • Asacol®, Ipocol®, Mesren® and Salofalk® work a little higher in the gut in the last part of the small intestine (called the ileum).

  • Pentasa® is designed to work along the entire length of the gut.

Which is the best one?

In general, medical studies show that aminosalicylates are probably equally effective. However, the evidence also suggests that sulfasalazine may cause more side-effects than the other types of aminosalicylates. Also, the one chosen may depend on the site and extent of your disease in the gut.

Continue reading below

Can I buy aminosalicylates or are they just on prescription?

These medicines are prescription-only and are usually prescribed by a specialist doctor.

How do I take aminosalicylates?

These medicines come in a variety of forms as mentioned above. Your doctor will advise you on how to take your medication, including how often. However, in general, the tablets or capsules should always be swallowed whole and not chewed. Read the leaflet that comes with your particular brand for detailed information.

You will usually need special monitoring for the first three months of your treatment, with checks every three months after that. This involves a blood test before you start taking the medication to see how well your liver and kidneys are functioning. Your liver function will then be checked every three months while you are taking the medicines.

If you take aminosalicylates for more than a year and you have no problems then you usually only need to have blood tests every six months.

You may also be encouraged to keep a record of the frequency of your bowel movements to check how well the medication is working.

How quickly do aminosalicylates work?

Aminosalicylates may work quickly - within a week or so - to deal with symptoms that come on suddenly. In other cases they may be used continually to help to keep symptoms away and prevent flare-ups.

How long is treatment needed?

This can vary depending on the reason for treating you. In some people these medicines are used to treat flare-ups. In others they may be used for a long time to keep symptoms away. You should talk to your doctor for advice on this

Who cannot take aminosalicylates?

Aminosalicylates may not be suitable for people with certain liver or kidney problems or for pregnant or breastfeeding women. People with a known allergic reaction to salicylates, such as aspirin, should not take these medicines. You should also inform your doctor if you have a sensitivity to sulfonamide, a chemical used in some diuretics and anti-inflammatory medicines.

A full list of people who should not take aminosalicylates is included with the information leaflet that comes in the medication packet. If you are prescribed an aminosalicylate, read this to be sure you are safe to take it.

Aminosalicylate side-effects

The most common side-effects when taking aminosalicylates are:

The side-effects most commonly experienced are minor and are generally not serious. However very rarely they can cause problems with your blood. You should discuss this with your doctor immediately if you have any unexplained bleeding, bruising, red or purple discolouration of the skin, sore throat, or a high temperature (fever), or if you feel generally unwell during treatment. Most people who take aminosalicylates do not have any serious side-effects.

Note: a rare but serious side-effect is an effect on the blood-making cells. If this occurs it can greatly reduce the number of blood cells in your body, including the cells that fight off infection and those that help to stop bleeding. Therefore, if you develop a sore throat, mouth ulcers, unexplained bruising or bleeding, rash, high temperature (fever) or any other signs of infection, stop the medicine and report this to your doctor immediately.

(As noted above, a mild rash is a common side-effect. The rash associated with this rare but serious effect on blood-making cells is different. Therefore, when taking these medicines always report a rash to a doctor who can then decide if it is a common and minor problem or the more serious rash.)

There are other rare side-effects. For example, in rare cases, some people taking aminosalicylates may have a hypersensitivity reaction. This may make you feel itchy, become more sensitive to sunlight or cause skin peeling. Sulfasalazine can cause a reduced sperm count in some men. This is reversible and sperm counts return to normal 2-3 months after stopping treatment.

For a full list of all possible side-effects and interactions associated with your medicine, read the leaflet that comes with your medication.

Other considerations

Sulfasalazine may change the colour of your urine and tears, making these fluids slightly orange. This can stain soft contact lenses in some people. If you wear contact lenses and need to take sulfasalazine it is usually recommended that you use glasses instead.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

symptom checker

Feeling unwell?

Assess your symptoms online for free