Diverticulitis is caused by swelling of a pouch that forms on the side of the colon (also called the large intestine). Diverticulitis affects 2-3 million Americans each year. Even though it is common, doctors still have important questions about the best way to treat people who have diverticulitis.

About 25%, or 1 in 4, of people have an episode of diverticulitis more than once. Some people find that worrying about possible future episodes gets in the way of enjoying their life. Other people have pain or other symptoms that don’t go away. For people whose diverticulitis are having negative effects on their lives, the COSMID trial is trying to answer this question:

“Is surgery more effective than best medical management for me?”

Treatment Options

There are two main treatments for diverticulitis – surgery or “medical management.” Surgery involves taking out part of the colon. “Medical management” can include diet and lifestyle changes, supplements, and prescription medications.


During surgery, the part of the colon affected by diverticulitis is removed. The remaining ends of the colon are reconnected. Most patients spend 3 to 5 days in the hospital. During this time, doctors and nurses work with patients to control their pain and make sure they can eat and drink before going home.

Potential Risks of Surgery:

  • Any surgery has risks. The most serious and rare problems may include: 
    • Infections or bleeding;
    • Leaking from the intestine where part of the colon was removed;
    • Needing a colostomy, where the colon is brought out to the skin to drain into a bag;
    • Damage to areas near the colon such as the tube that carries urine; and
    • Death (very rare).
  • More common problems are infection where the skin was cut and a longer than expected time spent in the hospital. Despite the risk of problems, surgery is considered safe and is one of the accepted approaches to treating diverticulitis.

Medical Management 

Medical management of diverticulitis may include:

  • Getting regular exercise;
  • Eating a high fiber diet;
  • Taking supplements like fiber and probiotics; and/or
  • Taking certain prescription drugs.

We think of these as tools in a medical management toolbox. Not everyone with diverticulitis will use all of these tools. Potential Risks & Benefits of Medical Management: • All the tools in the toolbox have been shown to improve symptoms or to lower the chance of diverticulitis coming back, for some people. • The tools do not work for everyone. • Some insurance companies may not pay for all of the tools. • Each of the tools has its own risks. Most risks are small. For example, antibiotics can cause a form of diarrhea called c. diff that can be treated. This does not happen often. The medical management toolbox is low risk and may make symptoms of diverticulitis better. But it’s not clear if these tools will keep diverticulitis from coming back. Surgery is more likely to keep diverticulitis from coming back, but it has more risks. The COSMID trial is trying to find of which treatment is better, and for whom.

The COSMID Trial

People taking part in the COSMID trial will be randomly assigned to one of two treatment options – surgery or medical management. Once their treatment has been assigned, they will work with their doctor to complete that treatment. The COSMID trial team will ask them about their experience and feelings on a regular basis during and after treatment. The COSMID trial team will report on many things about each treatment and the experiences of participants, such as:

  • How did each treatment improve (or not) quality of life?
  • How many repeat episodes of diverticulitis did patients have in each treatment group?
  • What was people’s experience in the healthcare system? For example, how many times did people in each group have to go back to their doctor? Go to the emergency room? Be admitted to the hospital?

For more complete details on the aims and procedures of the COSMID trial, visit clinicaltrials.gov.