Ketamine for Complex Regional Pain Syndrome (CRPS): A Deep Dive

Complex regional pain syndrome (CRPS) has been described as one of the most painful conditions a human being can experience — consistently ranking at the top of the McGill Pain Scale alongside childbirth and amputation. It's also notoriously difficult to treat. Which is why ketamine's growing evidence base in CRPS represents one of its most compelling therapeutic applications outside of psychiatry.

What Is CRPS?

CRPS is a chronic pain condition typically triggered by an injury, surgery, or nerve damage — but characterized by pain that is profoundly disproportionate to the original insult and often spreads beyond the initial injury site. The hallmarks include:

• Severe, burning, or electric pain — often described as "having your limb on fire"
• Allodynia: extreme pain from normally non-painful stimuli (like a light touch or clothing)
• Swelling, color changes, and temperature changes in the affected limb
• Changes in hair and nail growth, skin texture
• In severe cases, loss of motor function or spreading beyond the original limb

There are two subtypes: CRPS Type I (no confirmed nerve injury, formerly called reflex sympathetic dystrophy/RSD) and CRPS Type II (confirmed nerve injury, formerly called causalgia).

Why Standard Treatments Often Fall Short

Current CRPS treatments — nerve blocks, physical therapy, medications like gabapentin, tricyclic antidepressants, and opioids — provide partial relief at best for many patients and carry significant side effect burdens. The core problem is that CRPS is fundamentally a disorder of central sensitization: the nervous system has been "reprogrammed" to amplify pain signals, and treatments that address peripheral pain often fail to address this central dysregulation.

How Ketamine Works for CRPS

Ketamine targets central sensitization directly through NMDA receptor blockade. NMDA receptors in the spinal cord and brain play a critical role in "wind-up" — the process by which repetitive pain signals cause the nervous system to amplify pain perception over time. By blocking these receptors, ketamine essentially hits a "reset" on the hypersensitized pain circuits, sometimes producing dramatic and sustained relief even after the drug has left the system.

This is the same mechanism that makes ketamine effective for other central sensitization conditions (fibromyalgia, chronic migraine) but the evidence for CRPS is particularly robust.

The Evidence Base

CRPS is one of the best-studied ketamine indications outside of mood disorders:

• Correll et al. (2004): A landmark study showing that a 10-day outpatient ketamine infusion protocol produced significant and sustained pain reduction in CRPS patients, with relief lasting months in many cases.
• Schwartzman et al. (2009): Extended inpatient ketamine infusions produced dramatic relief in highly refractory CRPS cases, establishing proof-of-concept for ketamine's central mechanism.
• Sigtermans et al. (2009): A randomized controlled trial showing subanesthetic ketamine infusions produced significant pain reduction in CRPS compared to placebo.
• Multiple subsequent studies and systematic reviews have confirmed ketamine as one of the most effective interventions available for refractory CRPS, with a favorable risk/benefit ratio when administered appropriately.

IV Infusions vs. Sublingual Ketamine for CRPS

Most CRPS research has been conducted with IV infusions in clinical settings. It's worth being honest about where sublingual (at-home) ketamine fits in this picture:

IV ketamine infusions achieve much higher blood plasma levels than sublingual routes and are the standard for severe, refractory CRPS. For patients with severe CRPS, particularly those in crisis, IV infusions at a specialized pain clinic remain the gold standard.

Sublingual ketamine has lower bioavailability (approximately 25–35%) but offers meaningful advantages: convenience, ability to dose more frequently, lower cost, and no IV access requirements. For patients with mild-to-moderate CRPS or those maintaining relief achieved from infusions, sublingual ketamine may serve as a practical ongoing treatment or adjunct.

Some patients use a combined approach: initial IV infusions to "break" a severe flare, followed by sublingual ketamine for maintenance. Discuss your specific severity and history with your provider to determine the best approach.

What to Expect from Ketamine Treatment for CRPS

Results vary based on duration of illness (shorter duration generally predicts better response), severity, and individual neurobiology. Common patterns include:

• Significant reduction in baseline pain intensity (often 40–70% in responders)
• Decreased allodynia — touch and temperature become less excruciating
• Improved range of motion and function as pain allows more movement
• Relief that outlasts the drug itself, sometimes by weeks or months
• Secondary improvements in mood, sleep, and quality of life

Combining Ketamine with Physical Therapy

This is important: the neuroplasticity window after ketamine sessions is an opportunity to do physical therapy work that would otherwise be intolerable. Many CRPS specialists now combine ketamine with graded motor imagery and desensitization exercises, using the window of reduced central sensitization to retrain the nervous system's response to the affected limb. If you're pursuing ketamine for CRPS, working with a physical therapist familiar with central sensitization is strongly recommended.

If you'd like to explore whether at-home ketamine therapy is right for you, take our free 5-minute assessment to get started.