Ketamine Tablets for Complex Regional Pain Syndrome (CRPS)

Ketamine tablets for Complex Regional Pain Syndrome (CRPS) are used off-label, most often as maintenance therapy after a patient has already responded to a course of IV ketamine infusions. CRPS is a chronic pain condition, formerly known as reflex sympathetic dystrophy (Type I) or causalgia (Type II), that typically develops after an injury, surgery, or nerve damage. It causes burning pain, swelling, skin and temperature changes, and touch sensitivity that is far more severe than the original injury would predict. Ketamine works as an NMDA receptor antagonist, meaning it blocks a receptor in the spinal cord and brain that drives central sensitization, the process thought to sustain CRPS pain long after tissue has healed. Oral tablets are not a first-line treatment and are typically layered into a broader pain management plan that includes physical therapy and other medications.

Understanding CRPS

CRPS is classified into two types. CRPS Type I, formerly called reflex sympathetic dystrophy, develops without confirmed nerve injury, often following a fracture, sprain, or surgery. CRPS Type II, formerly causalgia, develops after documented nerve damage. Both types share core features: pain that is disproportionate to the original injury, sensory changes such as allodynia (pain triggered by normally non-painful stimuli like clothing or light touch) and hyperalgesia (an amplified pain response), and vasomotor, sudomotor, and motor changes in the affected limb.

The Budapest Criteria, adopted by the International Association for the Study of Pain (IASP), provide the diagnostic framework clinicians use to confirm a CRPS diagnosis. According to a review of CRPS mechanisms hosted by the National Institute of Neurological Disorders and Stroke (NINDS), the condition affects an estimated 26 per 100,000 person-years and occurs more often in women than men.

Why Ketamine Is Relevant to CRPS

CRPS involves several mechanisms where ketamine's pharmacology applies directly:

• Central sensitization. The NMDA receptor plays a central role in the process by which spinal cord and brain neurons become hyperexcitable, amplifying pain signals. Ketamine's primary action as an NMDA receptor antagonist targets this process directly.
• Neuroinflammation. CRPS involves elevated pro-inflammatory cytokines and glial cell activation. Ketamine has shown anti-inflammatory effects independent of its NMDA activity, including modulation of TNF-alpha, IL-6, and microglial activity.
• Wind-up and temporal summation. Repeated stimulation of pain pathways in CRPS can cause progressive amplification known as wind-up. NMDA receptors drive this process, and ketamine's blockade can interrupt it.
• Sympathetic-afferent coupling. Some CRPS presentations involve abnormal coupling between the sympathetic nervous system and sensory nerves. Ketamine does not target this directly, but reduced central sensitization may indirectly ease sympathetically maintained pain.

Evidence for Ketamine in CRPS

The strongest evidence for ketamine in CRPS comes from IV infusion studies. A 2009 randomized controlled trial by Sigtermans et al., published in the journal Pain, found that a 4-day continuous ketamine infusion produced significant pain relief lasting up to 12 weeks in CRPS patients. Multiple retrospective series have since reported response rates of 50-70% for IV ketamine in CRPS, and a Cochrane review has described the evidence as promising but limited by small study sizes.

Evidence specific to oral ketamine tablets is less developed but growing. Case series and retrospective studies report a 30% or greater reduction in pain on standard pain scales in roughly 40-60% of CRPS patients treated with oral ketamine, with benefit lasting from weeks to months during continued use. Some patients have been able to reduce or stop opioid medications after stabilizing on oral ketamine, and some report improved ability to participate in physical therapy.

The most common use pattern is maintenance therapy: patients who respond to an initial IV ketamine series are transitioned to oral tablets to sustain the benefit at home. A 2021 retrospective analysis published in Pain Medicine found that CRPS patients transitioned from IV to oral ketamine maintained their pain reduction significantly longer than those who received IV ketamine alone. See our comparison of oral and IV ketamine for more on how the two forms differ in onset, duration, and practicality.

Dosing Approaches for CRPS

Pain management with oral ketamine typically requires higher and more frequent doses than protocols used for depression. Most pain specialists start conservatively: 25-50 mg two to three times daily, increasing by 25 mg per dose every 3-7 days as tolerated, toward a target of 100-300 mg total daily dose divided into 2-4 doses. Total daily doses generally stay under 400 mg, though some specialists use higher amounts under close monitoring.

Consistent dosing matters for CRPS because the goal is steady NMDA receptor blockade; gaps in coverage can allow central sensitization to re-establish. Many providers space doses every 6-8 hours. How reliably a tablet is absorbed also affects how steady that blood level stays. See our guide on ketamine tablets and gut absorption and our research on medication adherence with ketamine tablets for more on why a consistent dosing routine matters.

What Patients Should Expect

Unlike IV ketamine, which can ease pain within hours, oral tablets usually take longer to show benefit. The first 1-2 weeks are typically a titration phase; many responders see consistent pain reduction by weeks 2-4, with a fuller assessment around weeks 4-8. In CRPS, success does not usually mean complete pain elimination. Realistic goals include a 30% or greater reduction in average daily pain, fewer or milder flares, better ability to participate in rehabilitation, reduced reliance on rescue medications, and improved sleep.

CRPS and depression frequently co-occur, with some studies estimating depression affects half or more of CRPS patients. Because ketamine can act on both pain and mood, it may simplify treatment for patients managing both conditions. Many CRPS patients are also on opioid therapy when they start ketamine; ketamine has been shown to reduce opioid tolerance and may enhance opioid analgesia, which should be managed carefully by the prescribing provider. Oral ketamine use in pediatric CRPS is limited and requires a specialist experienced in treating children.

Finding the Right Provider

Managing CRPS with oral ketamine works best with a provider experienced in both chronic pain management and ketamine prescribing, such as a pain medicine specialist, a neurologist focused on complex pain conditions, or a clinician at an academic center with a dedicated CRPS program. Insurance coverage for ongoing oral ketamine therapy varies and can affect whether maintenance treatment is sustainable long term; see our overview of the insurance coverage gap for oral ketamine tablets for what to expect.