Biologics work well for many people, but they have downsides. They're expensive, and they can have side effects and risks. You may get dizzy, feel sick like you've got a cold, or have a reaction where you get your shot. They can also lower your immune system's response. When you're taking one, let your doctor know if you get the flu or another infection. You'll be tested for tuberculosis before starting your biologic and checked while you're on it. You'll also get tested for hepatitis B and C. A biologic can raise your chances of getting lymphoma, a blood cancer, although this is rare.