context: Biologics are prescription drugs made from living organisms. Your doctor may prescribe one to you if other treatments haven't worked. Biologics work on your immune system. They target specific proteins in your body that cause inflammation. The FDA has approved these biologics to treat Crohn's disease: 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) Adalimumab, adalimumab-adbm, adalimumab-atto, certolizumab, infliximab, infliximab-abda, and infliximab-dyyb work on a protein called TNF-alpha that's part of the inflammation process. Natalizumab and vedolizumab work by stopping certain molecules in your immune system -- called integrins -- from attaching to other cells in the lining of your intestines. These drugs may ease symptoms of moderate to severe Crohn's disease. They may also help keep them from coming back. How they're given: A shot under your skin What are common side effects? Redness, swelling, itching, pain, rash, or bruising of the skin where you got the shot Upper respiratory or sinus infections Headache Nausea What are some other potential side effects? All biologics can have side effects, including infections like tuberculosis and sepsis. These drugs don't cause tuberculosis, but they may trigger it in people already exposed to it. A few people have gotten cancers like lymphoma. This drug also eases symptoms of moderate to severe Crohn's disease and helps to keep them from returning. How it's given: A shot under your skin What are the most common side effects? Rash Swelling Joint pain Upper respiratory tract infection Urinary tract infection What are other potential side effects? You may be more likely to get tuberculosis and sepsis. Your odds of getting other infections may be higher than most. Tell your doctor right away if you have an infection, or if you have a cough, fever, fatigue, or the flu. In rare cases, people get cancers like lymphoma. These drugs can lessen your symptoms. They may also help heal and lower your number of fistulas. These are abnormal connections between parts of your intestines, or from the intestines to your organs or skin. They often become infected and drain pus, mucus, or stool. How they're given: Your doctor will give them to you through an IV. What are the most common side effects? Redness, swelling, itching, pain, rash, or a bruise where the IV is given Upper respiratory or sinus infections Sore throat Headache Rash Nausea Coughing Stomach pain What are other potential side effects? Like with other biologics, there can be serious infections, such as tuberculosis and sepsis. It's rare, but some people have gotten cancers like lymphoma. Your doctor may recommend this drug if you have moderate to severe Crohn's disease with signs of inflammation. If you take it, you can't use other biologics or drugs that block your immune system. How it's given: Your doctor will give it to you through an IV. What are the most common side effects? Upper respiratory infections Urinary tract infections Headache Depression Fatigue Diarrhea Stomach pain Rash What are other potential side effects? This drug raises your odds of a rare but sometimes fatal brain infection called progressive multifocal leukoencephalopathy ( PML). It can also cause allergic reactions and liver damage. It's used to treat moderate to severe Crohn's disease. How it's given: Your doctor will give it to you through an IV or a shot. What are the most common side effects? Infections (urinary tract, yeast, upper respiratory) Feeling tired Headache Itching Redness where you got the shot What are other potential side effects? Like other biologics, ustekinumab may raise your odds of getting a serious infection or sepsis. There's also a chance of allergic reactions, serious lung inflammation, and certain types of cancer or nervous system disorders. It's used to treat moderate to severe Crohn's disease. How it's given: Your doctor will give it to you through an IV. What are the most common side effects? Upper respiratory infections Headache Joint pain Nausea Fatigue Fever Rash Pain in your hands and feet What are other potential side effects? Like other biologics, vedolizumab may raise your odds of getting a serious infection like tuberculosis or sepsis. There's also a chance of allergic reactions, liver damage, and a rare but sometimes fatal brain infection called PML. If your doctor prescribes a biologic, she'll want to see you often to make sure the treatment works safely and effectively. So be sure to go to all of your appointments. Tell your doctor about all prescription and over-the-counter drugs, supplements, or natural remedies you take. Any of those can affect the way other medications or supplements work. Talk to your doctor before you take anything new. Also tell your doctor about all of your medical conditions. Let her know if your symptoms get worse or if you notice any new ones.