Low dose naltrexone
Low dose naltrexone (LDN), where naltrexone is used in doses approximately one-tenth those used for drug/alcohol rehabilitation purposes, is being used as an "off-label" treatment for certain immunologically-related disorders. The use of LDN for such diseases as cancer was discovered and developed by Ian Zagon, PhD in animal and in vitro research, and LDN's broader clinical effects in humans were discovered by Bernard Bihari, MD.
The results of a successful open-label pilot study at Pennsylvania State University College of Medicine were reported to an international gastroenterology conference in Los Angeles in May 2006. The trial demonstrated the safety and efficacy of LDN in a group of patients with Crohn's disease, a classic autoimmune disorder.  Dr. Jill Smith, Professor of Gastroenterology at Pennsylvania State University's College of Medicine, found that two-thirds of the patients in her pilot study went into remission and fully 89% of the group responded to treatment to some degree. She concluded that "LDN therapy appears effective and safe in subjects with active Crohns disease." Smith and her colleagues have since received a substantial NIH grant and are proceeding with a definitive Phase II placebo-controlled clinical trial.
In addition, there is some in vitro data that indirectly suggest the potential benefits of LDN therapy. Many anecdotal accounts and case reports have also been cited in favor of LDN therapy. Some of the many conditions for which LDN has been reported as beneficial include multiple sclerosis, Crohn's disease, HIV/AIDS, chronic fatigue syndrome, irritable bowel syndrome, psoriasis, fibromyalgia, ALS, autism in children, and cancer. Several clinical trials have been planned and a few are currently taking place.
Also there is a book available about the self-treatment of chronic alcoholism using LDN (see link below).

# Pharmacology
LDN has been theorized to work in multiple modalities. Without formal studies, there is no formal conclusion as of yet, but the generally accepted theory posited originally by Dr. Bihari is as follows:
Beta-endorphins are important regulators of the immune system. Naltrexone, which is a pure antagonist to narcotics, causes an artificial blockade of the endorphin/opioid receptors in the brain. However, unlike the normal (~50mg) dose of naltrexone used to treat drug addiction, which maintains this blockade continuously for 24 hours (preventing any derived pleasure from taking the forbidden drugs), low dose naltrexone (~3mg to 5mg) blocks the endorphin receptors for only a few hours. During that time, endorphins fail to attach to the receptors and the body apparently compensates by creating more. (Note that Dr. Bihari prescribes LDN to be taken at bedtime to take advantage of the body's pre-dawn boost in endorphin production.) Once the low dose naltrexone dose has been metabolized, the body is left with a "normal" amount of endorphins as compared to healthy controls, which consequently normalizes the immune function.
This theory of LDN's mechanism contradicts the widely-held belief that autoimmune diseases are caused by an overactive immune system. However, since 2005, at least 3 separate scientific reports have described an underlying immunodeficiency as being characteristic of four different autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, Crohn's disease and chronic fatigue syndrome. In addition, recent scientific research has demonstrated abnormally low beta-endorphins in all forms of multiple sclerosis.
In April of 2007 a LDN conference was held at the National Cancer Institute. Several lecturers were present discussing the use of LDN in Crohn's disease, multiple sclerosis, general autoimmune disease, and cancer. One participant, Burton M. Berkson MD PhD of Las Cruces, New Mexico discussed his successful experience treating metastatic pancreatic cancer and B cell lymphoma with LDN at bedtime.
Dr. Berkson described one patient who was diagnosed with "terminal"  and metastatic pancreatic cancer at a well-respected oncology center. After treatment with a healthy life style program and LDN at bedtime he is alive, well, and back at work almost 5 years after diagnosis. Today, he is described as free of symptoms.
Another patient with greatly enlarged lymph nodes in his neck, axillae, and groin and diagnosed with a B cell lymphoma was found to be free of signs and symptoms after 6 months of LDN therapy.In his presentation, Dr. Berkson used before and after CT and Pet scans to show improvement, or reversal, of the disease process in four patients.

# Controversy
LDN is a low-cost drug that is unlikely to enjoy ironclad patent protection. Many patients, who have benefitted substantially from the medication, suspect that clinical trials of LDN have been discouraged by the pharmaceutical companies, which prefer selling high-margin, patent-protected drugs. These claims are unsubstantiated at this time.