context: After you've tried other treatments for Crohn's disease, your doctor may suggest drugs that target your immune system. Besides that, they can help prevent flare-ups. The goal is to ease inflammation in your gut. Inflammation is part of a complicated process that helps cause your Crohn's. Drugs that affect your immune system, and treatments like steroids and antibiotics, can treat that process. There are several reasons your doctor might want you to try immune system drugs to treat your Crohn's: Because other drugs don't work. Or your doctor may not want you to become too dependent on steroids to lower inflammation. To keep flares away. Immune system drugs can help keep your Crohn's symptoms from coming back. It may take up to 3 months before they take effect. To treat a fistula. This type of abnormal connection can go from one part of your intestine to another. It can also go from your digestive system to places like your bladder, vagina, anus, or skin. If you're having a flare, the doctor might combine one of these drugs with steroids to speed up treatment and ease your symptoms. You may hear your doctor refer to one type: immunomodulators. These affect your entire body, not just your gut. Some common ones are: Azathioprine ( Azasan, Imuran) Mercaptopurine ( Purinethol, Purixan) Methotrexate ( Trexall) Azathioprine and mercaptopurine can help keep flare-ups at bay. But they may take months to work. You might a need a faster-acting drug like a steroid until they do. Methotrexate can help when steroids or other drugs don't work anymore. Its side effects include: Nausea and diarrhea Fatigue Scarring of the liver if used long-term Your doctor may use these drugs aggressively to treat your symptoms. Then, he may switch you to other drugs for long-term treatment. You and your doctor can talk about which approach makes sense for you. These drugs also affect your immune system. But they focus just on parts of your immune system in your gut. Doctors use biologics if you have moderate to severe Crohn's that hasn't responded well to other medications. They also use them to treat open, draining fistulas in combination with antibiotics and other treatments. Some examples of biologics are: Adalimumab ( Humira) Adalimumab-adbm ( Cyltezo), a biosimilar to Humira Adalimumab-atto ( Amjevita), also a biosimilar to Humira Certolizumab ( Cimzia) Infliximab ( Remicade) Infliximab-abda ( Renflexis), a biosimilar to Remicade Infliximab-dyyb ( Inflectra), also a biosimilar to Remicade Natalizumab ( Tysabri) Ustekinumab ( Stelara) Vedolizumab ( Entyvio) In most cases, biologics cause fewer problems than other drugs used for Crohn's disease. In some instances, there can be serious side effects. Also, there is a risk for serious infections and certain types of cancer in people who take these drugs. Talk with your doctor about which medicine is right for you. No matter which one your doctor prescribes, he'll watch you carefully. Before you take one of these drugs, let your doctor know if you have a heart condition or a disease that affects your nervous system. You may have side effects where you get the shot, such as: Redness Itching Bruising Pain Swelling Other possible side effects include: Headache, fever, or chills Trouble breathing Low blood pressure Hives or rash Stomach or back pain Nausea Cough and sore throat