On the other hand, despite their potential effectiveness, treatment with drugs that weaken the immune system may cause severe side effects. Increased risk of infection is a common side effect of all the immunosuppressant drugs. The immune system protects the body from infections. When the immune system is suppressed, infections are more likely to happen. Some of these infections are potentially dangerous. Because the immune system protects the body against some forms of cancer, immunosuppressant drugs are also associated with a slightly increased risk of cancer. For example, long-term use of immunosuppressant drugs may carry an increased risk of developing skin cancer as a result of the combination of the drugs and exposure to sunlight. The immunosuppressive drugs are very powerful and can cause serious side effects such as high blood pressure, kidney problems, and liver problems. Some side effects may not show up until years after the medicine is used.