Here's the "boring" background:   Naltrexone HCl was approved by the FDA in 1984 for the treatment of opioid ("narcotic") addiction. Naltrexone 50 mg. tablets block opioids from stimulating their receptors to prevent a "high" for addicts. Of course, if someone takes 50 mg. of naltrexone, it would also block opioids from achieving their legitimate purpose of relieving pain.

But here's where it starts to get interesting: Low Dose Naltrexone (LDN) - in doses of 4.5 mg. which are approximately 1/10th of the opioid addiction treatment dose of 50 mg. - exhibits paradoxical properties, such as relieving pain and inflammation. That's important, because LDN has been show to induce remission of Crohn's Disease in adults and children, and no serious side effects were reported. That is great news for patients who suffer from this painful, difficult-to-treat, inflammatory bowel disease.

LDN has reduced symptom severity in conditions such as fibromyalgia, multiple sclerosis, and complex regional pain syndrome. The researchers report that LDN may operate as a novel anti-inflammatory agent in the central nervous system, via action on microglial cells. These effects may be unique to low dosages of naltrexone and appear to be entirely independent from naltrexone's better-known activity on opioid receptors. LDN may represent one of the first "glial cell modulators" to be used for the management of chronic pain disorders.

And the most intriguing part:  Low Dose Naltrexone (LDN) has been shown to increase the effects of opioid growth factor (OGF), which inhibits DNA synthesis in cancer cells, slows the growth of cancer cells, and triggers immune-related death of cancer cells. OGF has been the subject of several preclinical and Phase I and II clinical trials in pancreatic and hepatocellular cancers (and published case reports in neuroblastoma and hepatoblastoma), as well as pre-clinical research in ovarian cancer.  

The above information about Low Dose Naltrexone is based on studies of small groups of patients, but as you can see these recent references, this is a hot topic and lots of research is ongoing. Since LDN is not commercially available, the medication used in these studies must be compounded.