LDN is a somewhat experimental treatment that many have found useful for treating diseases such as multiple sclerosis, cancer, and even liver disease.
The drug is actually an anti-opiate. It blocks the uptake of opiates in the brain. When you take a very very low dose (like 3 mg) the opiates in your brain are actually only block for about one or two hours. Your brain then actually produces more opiates in the form of endorphins. The idea is that people who are fighting disease are low in endorphins and that's bad for the immune system