context: If you have moderate to severe psoriasis, your doctor may suggest a systemic drug -- medicine that affects your whole body. They're typically used when the skin condition covers more than 5% to 10% of your body and other treatments haven't worked. While systemic treatment can help, many can cause serious side effects. Your doctor will want to keep a close eye on you while you take the medicine. Retinoids. These are made from vitamin A and affect the way your skin cells grow and are shed. Most doctors prescribe one called acitretin ( Soriatane). If you have plaque psoriasis -- inflamed, red skin with silvery scales -- a retinoid works best when used with phototherapy. On its own, it works well to treat pustular psoriasis -- a breakout of sore, red blisters or pus bumps -- and erythrodermic psoriasis in which most of your skin looks very red and peels as if it's burned. This medication can cause serious birth defects even after you stop taking it. Don't take it if you're pregnant or plan to get pregnant within 3 years. Methotrexate. This drug eases symptoms by curbing your immune system and slowing the growth of skin cells. You take it once a week either by mouth or in a shot, and you should notice changes after 4 to 6 weeks. But this drug can have serious side effects. At first, you might have nausea or fatigue, and over time, it can damage your liver and blood cells. Tell your doctor about any other health issues you have. Methotrexate isn't safe for people who have anemia or liver disease. You should also watch how much alcohol you drink. Even one glass a day while you're on it can cause liver problems. You'll need regular blood tests so your doctor can check on your blood cells and liver. You'll need to take it with daily folic acid to reduce side effects. Both men and women should stop taking it if they plan to start a family. Cyclosporine. This drug lowers your immune system. It also slows skin cell growth. It's used only for severe cases of psoriasis when nothing else seems to work. You take it by mouth. While it can help clear psoriasis, cyclosporine's benefits typically end when you stop taking it. It also can lead to kidney problems, high blood pressure, and high cholesterol. You shouldn't take it if you have a weak immune system or if you're breastfeeding. You should also avoid it if you're treating your psoriasis with a form of phototherapy called PUVA. Because of the side effects, experts don't recommend taking the drug for more than a year at a time. Apremilast ( Otezla). This is a newer drug used just for diseases that cause long-term inflammation, like psoriasis and psoriatic arthritis. It shuts down an enzyme in your immune system, and that slows other reactions that lead to inflammation. It comes in pill form. Biologics. If your psoriasis is severe or other treatments haven't worked well enough for you, your doctor might recommend one of these drugs. They affect specific parts of your immune system that play a role in psoriasis. These include: adalimumab ( Humira), certolizumab ( Cimzia), etanercept ( Enbrel), guselkumab ( Tremfya), tildrakizumab ( Ilumya), infliximab ( Remicade), ixekizumab ( Taltz), risankizumab ( Skyrizi), secukinumab ( Cosentyx), and ustekinumab ( Stelara). Because your immune system may not work as well as it should while you take these drugs, you may be more likely to get infections or certain diseases. So your doctor may not prescribe them if your immune system is already weak because of a health condition or other medication you take.