02/08/2026
Anyone who's been a patient in my practice long enough has likely heard my spiel on low-dose naltrexone. In response to a patient question online, I put together this little story with the help of GPT. It's a great origin story for this therapy, so I wanted to share it here: Low-Dose Naltrexone (LDN) for CRPS — where did this idea even come from?
CRPS is one of the most frustrating pain conditions we treat. Historically we’ve thrown *everything* at it: nerve blocks, ketamine, spinal cord stimulators, opioids, PT, desensitization… and still many patients struggle.
So how did a tiny dose of an addiction medication end up in the CRPS conversation?
Here’s the real origin story 👇
For years, chronic pain was thought of mainly as a *nerve problem*. But in the late 1990s–2000s, pain research started shifting toward something bigger: the immune system inside the nervous system.
Meet the microglia.
Microglia are immune cells living in the brain and spinal cord. When they get activated, they release inflammatory chemicals that amplify pain signals and drive central sensitization — the “volume k**b stuck on high” phenomenon.
CRPS started looking less like a simple nerve injury and more like a **neuro-immune disorder**.
Researchers found evidence of:
• Elevated inflammatory cytokines
• Glial activation in the spinal cord
• Small fiber neuropathy + immune involvement
• Autoantibodies in some patients
• Post-traumatic and post-viral triggers
In other words, CRPS checked *all* the neuroinflammation boxes.
Then came the surprise discovery.
Around the mid-2000s, researchers realized that naltrexone — the medication used at high doses to block opioids and alcohol — does something completely unrelated to addiction treatment.
It blocks a receptor on microglia called **TLR4**.
TLR4 is basically a “danger alarm” switch for the nervous system. When it’s activated, microglia release inflammatory chemicals that worsen pain, allodynia, fatigue, and hypersensitivity.
Even more interesting: opioids can *activate* TLR4 and worsen central sensitization over time. Naltrexone does the opposite.
So suddenly researchers had a cheap, generic drug that might calm neuroinflammation.
Enter CRPS.
Around 2013, a Stanford group treated a couple of severe, treatment-resistant CRPS patients with **low-dose naltrexone** (typically 1–4.5 mg instead of the usual 50 mg). These were patients who had already failed major therapies.
They improved — significantly.
Those case reports spread fast through pain medicine because CRPS is notoriously difficult to treat and options are limited.
Since then, many clinicians have quietly tried LDN off-label in CRPS.
What’s interesting is that it doesn’t behave like a typical pain medication.
It doesn’t work overnight.
It doesn’t feel like a painkiller.
Instead, patients often describe gradual, global improvements over weeks:
• Less allodynia
• Reduced burning pain
• Improved sleep and fatigue
• Decreased “sickness behavior”
• Better temperature/color changes
• Gradual functional gains
It behaves more like a **disease-modifying modulator** than an analgesic.
The leading theory today:
LDN may help CRPS primarily by calming neuroinflammation and reducing central sensitization. A secondary theory is that brief opioid receptor blockade triggers a rebound increase in natural endorphins.
The evidence is still evolving (because it’s cheap and off-patent, so large trials are limited), but in real-world pain medicine, CRPS has become one of the conditions where LDN is most commonly considered.
Medicine often advances this way: observation → mechanism → early studies → clinical adoption.
LDN in CRPS is a perfect example of that path.
