I have an anecdotal story. I take a variant of the b-3 vitamin (Nicotinamide Riboside , or NR). It has GRAS status (NIH) and a Letter of No Objection from the FDA, and can be purchased on-line in the US. NR is the only B-3 that can enter the neuronal cells (unlike niacin and niacinamide). NR is a precursor to NAD, a key coenzyme within the cells that is important regarding mitochondrial function.
I occasionally tell people who I casually meet about NR, because of the benefits I have experienced, the reports from other people I know or whose comments I have read, and the mostly animal efficacy trials that I have read. In the relevant instance I brought up NR to a woman from France who I met not eh Oregon coast. She interrupted me and told em that she had been taking NR. She said that she had Lyme disease induced neuropathy pain so bad in her legs that she had been unable to walk. Her doctor in France had read about NR, and said that she had no remedy, but recommended giving NR a try because of its potential benefits regarding neurological situations. She said that after taking 500 mg of NR per day for a few months that the pain had completely vanished, and that she continued taking it.
I personally take 1000 mg of NR per day, without any negative reaction. For me it has ended the muscle stiffness that I sued to feel int he mornings or after sitting too long. My triglycerides and Ac have also improved to normal levels.
There is a lot on-line about nicotinamide riboside. As I understand, t here are currently 18 human efficacy trials registered with the federal government.