This post is prompted by a video [1] of Bernard Bihari, MD, who essentially owns the LDN concept. (Thankyou Terry for sending the link.) It is a long interview.
I was a member of the LDN group some years ago, & I can't say that I got anything out of it. No anecdotal reports of significant benefit from men with PCa.
The LDN concept is simple enough. Naltrexone was developed for drug users. It blocks opioid receptors & prevents a high. It was "approved by the FDA in 1984 in a 50mg dose for the purpose of helping heroin or opium addicts" [2].
A side effect of Naltrexone is that it stimulates production of endorphins, which are the natural ligands of opioid receptors. This is all to no effect when the receptors are blocked. However, the same degree of endorphin production occurs at lower doses, down to about 3mg. At 3mg, the effect on the opioid receptors is minimal. This is the basic LDN dosage, however some need a little more; some could go a bit lower.
Endorphins stimulate the immune system. There are conditions ranging from chronic stress to AIDs where endorphins are much reduced in the body. It would seem obvious that LDN might profitably regulate the immune response in those cases.
It appears that there is no commercially available test for endorphins.
I remember one of the co-founders of 'Us TOO' claiming that stress caused his PCa. It may be pointless pinpointing "the" cause when there are so many risk factors, including bad luck (random mutations), but stress shouldn't be ignored. Perhaps men in stressful work or personal situations would benefit from LDN as a prophylactic?
Maybe work stress contributed to my PCa? But I retired 17 years ago. I don't feel stressed. How would I benefit from LDN? But perhaps cancer itself can suppress endorphins & the immune response?
"In the mid-1990's, Dr. Bihari found that patients in his practice with cancer (such as lymphoma or pancreatic cancer) could benefit, in some cases dramatically, from LDN. In addition, people who had an autoimmune disease (such as lupus) often showed prompt control of disease activity while taking LDN." [2]
From a 2016 British study [3]:
"It has been reported that lower doses of the opioid antagonist naltrexone are able to reduce tumour growth by interfering with cell signalling as well as by modifying the immune system. We have evaluated the gene expression profile of a cancer cell line after treatment with low-dose naltrexone (LDN), and assessed the effect that adapting treatment schedules with LDN may have on enhancing efficacy. LDN had a selective impact on genes involved with cell cycle regulation and immune modulation. Similarly, the pro-apoptotic genes BAD and BIK1 were increased only after LDN. Continuous treatment with LDN had little effect on growth in different cell lines; however, altering the treatment schedule to include a phase of culture in the absence of drug following an initial round of LDN treatment, resulted in enhanced cell killing. Furthermore, cells pre-treated with LDN were more sensitive to the cytotoxic effects of a number of common chemotherapy agents."
Perhaps there is a softening-up role for LDN with Taxotere, etc. Or with immunological treatments?
LDN is presumably not to be used with prednisone.
-Patrick
[1] youtube.com/watch?v=rll1A3a...
Dendritic Cell Therapy 
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