Since I couldn't handle gabapentin, my rheumatologist decided to offer me LDN, also known as Low Dose Naltrexone.

Anyone reading along may be surprised, because at high doses, naltrexone has been used to treat drug addiction to opiates. But some research has been done which determined that at low to very low doses, the same drug works to treat pain, and in particular, fibromyalgia.

I have been differentially diagnosed with fibromyalgia, so what I say here may be useful to you -- but usual disclaimer of what works for others may not work for you:

Low dose naltrexone has been studied for treated fibromyalgia at Stanford University, and so far, the results have been promising:

Low-Dose Naltrexone Reduces the Symptoms of Fibromyalgia
Low-Dose Naltrexone Reduces the Symptoms of Fibromyalgia - Stanford Systems Neuroscience & Pain Lab - Stanford University School of Medicine

Low-dose naltrexone for the treatment of fibromyalgia: findings of a small, randomized, double-blind, placebo-controlled, counterbalanced, crossover trial assessing daily pain levels.
Low-dose naltrexone for the treatment of fibromyalgia: findings of ... - PubMed - NCBI

They've conducted a couple studies, the results are very promising, and because of this, some rheumatologists are now independently prescribing LDN to their patients with fibro and other conditions where muscle and nerve pain are present.

The good things about it:
- It's cheap compared to other drugs used to treat fibro, especially if you have to pay out of pocket.
- Side effects profile is extremely low, unlike other pain meds, and they usually only last the first 2-3 weeks.
- Dosing is easy. One dose taken at night right before bed.
- There have been plenty of studies done on naltrexone itself (though at much higher doses) so it isn't a new drug per se, and more is known about its safety and efficacy.

The bad things about it:
- You must stop ALL opiate pain medicines for 2 weeks (longer is better, as side effects risk decreases the more you're weaned off opiates) before you can get on LDN. LDN works on opiate receptors in the brain, and opiate pain meds will block LDN from working.
- You can't just pop over to Walgreen's and get it. You have to order it from a compounding pharmacy.
- It can stop working after a while, or after a long time of use one may get restless on it and find they do have some side effects. If this happens, one may have to back off on it and take less, or take it every other day or even less often. There's some evidence it builds up and one no longer needs a steady dose.
- It can be tricky to manage around thyroid medication. There's some evidence it can help 'correct' autoimmune thyroid, and people who have this condition and take, say, Synthroid and/or Cytomel or Armour have to begin tapering down their dose of thyroid meds while on LDN or they will develop hyperthyroidism.
- Not all doctors will prescribe it, for whatever reason -- even though side effects and risks are pretty low. You may have to look for someone who has a relationship with a teaching hospital or medical school; someone who is open to prescribing it and more importantly, following up with you while you take it.

This is personal opinion only: I have gotten more relief for pain out of LDN than I did from gabapentin, and I got more relief out for pain out of it than the opiates I've had (Vicodin, Tramadol, others). It may be that for all my complaining about neuropathy now, I just need to get back on the LDN and try it again (It was making me anxious and restless, during a time when my anxiety was already getting severe, I stopped because I hoped the anxiety would lessen. It has somewhat.)

Those who have been enrolled in the studies reported major decreases in pain. I don't want to oversell this, though, because note that it did not work for everyone to the same high degree, and the above groups are small study groups. What is needed is a large clinical trial, but it's unlikely one will be conducted due to expense and lack of profitability. (Cross your fingers that I'm wrong there.)

Hope this answered your question. Maybe LDN is something that could help you, maybe not. Talk to your doctor/specialist about it, or someone who specializes in LDN treatment.