Lauren, doctors usually rely on clinical trials when deciding whether or not to prescribe a drug. There have not been any large-scale trials of LDN, and probably never will be, because clinical trials are expensive to run and no drug company will ever get a return for their investment because naltrexone is past its patent and is now a generic drug, ie any little drug company can make it and sell it. It's sad, but that's how the system works. Maybe I'm cynical, but I imagine that the big drug companies, eg the ones that manufacture and market the CRAB drugs, are actively discouraging independent studies into LDN in MS, because it threatens their market. And anyone who wants to try LDN has to stop taking Avonex or Betaferon. That's why you might have more luck with your GP than your neurologist. I recommend a really good round-up for doctors here: http://www.gazorpa.com/LDNFAQ.html
It's brief, sensible, well-researched and well-written, and it was enough to convince my GP. Good luck!