Ivermectin is a medication that is effective against many types of parasites. It is used to treat head lice, scabies, river blindness, strongyloidiasis, and lymphatic filariasis, among others. It can be either applied to the skin or taken by mouth. The eyes should be avoided. Common side effects include red eyes, dry skin, and burning skin. It is unclear if it is safe for use during pregnancy, but is likely acceptable for use during breastfeeding. It is in the avermectin family of medications and works by causing an increase in permeability of cell membrane resulting in paralysis and death of the parasite. Ivermectin was discovered in 1975 and came into medical use in 1981. It is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system. The wholesale cost in the developing world is about US$0.12 for a course of treatment. In the United States it costs $25–50. In other animals it is used to prevent and treat heartworm among other diseases.