If you have a more severe form of psoriasis, medicines taken by mouth or injection can help bring your condition under control. This is called systemic treatment because it works inside your body. Common Options The oral medicine cyclosporine helps psoriasis by “quieting” your immune system. It can be very effective if you have difficult-to-treat psoriasis of the skin and nails. If you take this medicine, you’ll need to have your kidneys and blood pressure checked regularly. Because of possible side effects such as kidney damage and high blood pressure, you should not use cyclosporine for more than a year at a time. It can be switched with other psoriasis medicines. Tip: Steer clear of grapefruit and grapefruit juice while on this medicine. The fruit raises the levels of cyclosporine in the blood. The anti-cancer drug methotrexate is also a proven treatment to fight psoriasis. It works by blocking some activities of your immune system. This helps slow skin turnover and reduce inflammation. You take it weekly by mouth or as a shot. Like other systemic treatments, it can have serious side effects, such as liver damage and birth defects. Retinoids like acitretin are made from a manufactured form of vitamin A. These oral medicines work by bringing the growth of skin cells back to the normal range. However, they can cause significant side effects, such as liver damage, muscle aches, and severe headaches. 6-Thioguanine is an oral medicine also used to treat leukemia. It works nearly as well as methotrexate and cyclosporine for psoriasis, with fewer side effects. But if you take it, you may develop anemia, or low red blood cells. Hydroxyurea, also a cancer medicine, is not quite as effective against psoriasis as methotrexate and cyclosporine. Your doctor may prescribe this oral medicine along with light therapy. One drawback: It can lower your levels of red and white blood cells. Newer Treatments: Biologics These medicines, also known as biologic response modifiers, are newer options if you have moderate to severe psoriasis and psoriatic arthritis. They work by interrupting how your immune system works. Biologics are made from proteins produced by living cells. Examples of these medicines are adalimumab, infliximab, ixekizumab, secukinumab, ustekinumab, and etanercept. Some of these drugs can help slow the joint damage of psoriatic arthritis. You take these medicines by shot or intravenous line (IV). You’ll need to see your doctor regularly because these medicines weaken your immune system. Tips for Taking Systemic Medicines To avoid dangerous interactions, tell your doctor about all the medicines, herbs, and supplements you take. Try not to skip your scheduled blood tests or other tests to check for medication side effects. Men and women: Be sure to tell your doctor if you’re planning a family. Many of these medicines can cause birth defects and should not be used by people attempting a pregnancy.