Book excerpt: Naltrexone is an opiate antagonist drug developed in the 1970s and approved by the FDA in 1984 for opiate and drug abuse treatment. When used at much lower doses in an off-label protocol referred to as low dose naltrexone (LDN), the drug has been shown to halt disease progression in Crohn's disease and certain cancers, to reduce symptoms in multiple sclerosis and autism, and to improve numerous autoimmune and neurodegenerative conditions, including Parkinson's disease and amyotrophic lateral sclerosis (ALS). Grounded in clinical and scientific research, this book describes the history of naltrexone, its potential therapeutic uses, its effects on the immune system, its pharmacological properties, and how the drug is administered. It also lists fillers and compounding pharmacies, doctors who prescribe LDN, and patient resources, and includes interviews with LDN patients and researchers.