The LD is for Low Dose and it has a short half life of 4 hours, though sensitive can vary by an order of magnitude so how long it lasts can depend. Typically people start low and slowly build up. You don't notice the initial effects (unless you're unfortunate enough to need opioids during that time), it's the subsequent bodies reaction overnight that has the real effect. Most healthy people don't notice anything good or bad. Sick people can get a variety of effects and some quite strong but very rarely an emergency.

Anecdotally it appears that if you get a strong effect then it is likely it'll be more beneficial long term. Most common effects are nausea which generally subsides in a few weeks, extremely vivid dreams that you can remember which lasts longer. Basically low grade serotonin sickness and perhaps some dopamine dysregulation - some people do get dopamine surges. It helps normalize neurotransmitter levels and your brain might not be used to it. Usually you sleep less but feel more refreshed. I had one of the rarer reactions which was extreme energy, I started LDN for ME/CFS and thought it had cured me and that I now had a new problem of too much energy. Unfortunately it wore off after a few weeks, but it did plateau to a higher baseline.

Naltrexone gave me the rarest side effect - seizures, and that's extremely rare because it generally bolsters seizure threshold. It surprised my doctor. About 3 months into taking it I had a complete absence seizure at work while operating a 1kW LASER. The thing's supposed to fire for a split second, I had it happen just as I was hitting the fire button, kept the fire button held with my body for just short of a minute. I came to from the smell of vaporizing metal hitting my nose. Whoops, $10K experimental board wrecked.

As soon as I got off the medication and let it clear out of my body for a month, I quit having auras or any other odd seizure-related symptom. Damn glad that didn't happen while driving.

The one side effect I’ve heard from my doctor who has patients on LDN, that fortunately seems fairly rare, but that can catch people off guard is sudden depression. People a few days to a week into starting it suddenly having uncontrollable crying and other things. Apparently corrects quickly after stoping so not something to be afraid of so long as aware. LDN seems to help a lot of people.

Can’t take it with any opioids. Plus side. I no longer needed opioids (tramadol) to manage pain.

I wake up with energy in the morning. First few months it was like viagra on steroids in morning. That eventually calmed down.

Otherwise I’ve had no side effects, and I tend to get all the crazy side effects of almost every medication.