Lamisil (also known as terbinafine) is an antifungal drug most often used to treat fungal infections of the fingernails and toenails. Because these infections are very difficult to treat, the drug needs to be taken for weeks. Although most people can take Lamisil without side effects, the drug can cause liver damage and heart failure. Most experts recommend that people taking Lamisil have a blood test done every four to six weeks to look for liver damage. If the blood levels get too high the drug is stopped.

Although people can have different symptoms from liver damage, fatigue and itching are commonly seen, especially in combination with decreased appetite and a yellowing of the skin and whites of the eye. The liver damage can be serious. People who take Lamisil who develop yellowing of the skin or whites of the eyes, itching and other signs of liver damage should contact their physician. A simple blood test can be done to see if Lamisil has caused a problem. The liver is good at repairing itself, so the problem usually goes away when Lamisil is stopped. But it doesn't go away in all cases. The U.S. Food and Drug Administration issued a warning in 2001 about liver damage with Lamisil. At that time, 16 people had suffered serious liver damage from Lamisil and a related drug called itraconazole.