Racemic ketamine is the original form of ketamine, containing a 50/50 mix of its two mirror-image molecules: R-ketamine and S-ketamine. It has been FDA-approved since 1970 as an anesthetic, and in recent years it has become widely used off-label for treatment-resistant depression, chronic pain, and other psychiatric conditions. Understanding what “racemic” means, and how this form differs from newer ketamine-based treatments, helps make sense of a rapidly evolving treatment landscape.
What “Racemic” Actually Means
Many drug molecules exist in two forms that are chemically identical but mirror images of each other, like left and right hands. These are called enantiomers. Ketamine has two: S-ketamine (the “left hand”) and R-ketamine (the “right hand”). When a drug contains both enantiomers in equal proportion, it’s called a racemic mixture.
Racemic ketamine, sometimes written as (R,S)-ketamine, is what hospitals and clinics have used for decades. It’s the version most people mean when they simply say “ketamine.” Each enantiomer behaves slightly differently in the brain, which is why some researchers have suggested that an ideal therapeutic ratio might actually lean toward more R-ketamine than S-ketamine, potentially in the range of 2:1 to 4:1. But the standard pharmaceutical product remains a straight 50/50 split.
How It Works in the Brain
Ketamine primarily blocks a receptor in the brain called the NMDA receptor, which is part of the glutamate signaling system. Glutamate is the brain’s main excitatory chemical messenger, and the NMDA receptor plays a central role in learning, memory, and mood regulation. Ketamine works as what pharmacologists call an “open channel blocker,” meaning it only plugs the receptor when the channel is actively open. This makes it act more like a volume dial than an on/off switch, turning down excessive signaling without silencing it completely.
One promising theory for its antidepressant effects involves a brain region that functions as an “anti-reward center.” In depression, certain neurons in this area fire excessively, reinforcing negative emotional states. Ketamine appears to quiet that overactivity. The result, for many patients, is a rapid lift in mood that traditional antidepressants, which typically take weeks to kick in, simply can’t match.
FDA-Approved and Off-Label Uses
Racemic ketamine is FDA-approved for one thing: induction and maintenance of general anesthesia. That’s it. Every other use, including treatment of depression, anxiety, PTSD, chronic pain, and suicidal ideation, is considered off-label. This distinction matters because it means the FDA has not formally evaluated ketamine’s safety or effectiveness for psychiatric conditions, and no standardized dosing guidelines exist for these uses.
Despite this, off-label ketamine treatment has grown enormously. Hundreds of clinics across the United States offer IV ketamine infusions for depression, and compounded ketamine products (including lozenges, nasal sprays, and oral formulations) have become increasingly common. The FDA has issued warnings about compounded ketamine products specifically, noting that they have not been evaluated for safety, effectiveness, or quality.
What a Typical Infusion Looks Like
For depression, racemic ketamine is most commonly given as a slow intravenous infusion. The standard dose is 0.5 milligrams per kilogram of body weight, delivered over 40 minutes. For a 150-pound person, that works out to roughly 34 milligrams. Clinicians monitor vital signs continuously throughout the session, and the dose can be adjusted down (often to 0.4 mg/kg) if a patient becomes distressed. The goal is typically to reach a mild dissociative state, a floating, dream-like feeling, which serves as a marker that the dose is in the right range.
Most treatment protocols involve a series of infusions over two to three weeks, sometimes followed by maintenance sessions spaced further apart. The drug is eliminated from the body relatively quickly, with a half-life of two to three hours. Women may clear it about 20% faster than men. The liver does most of the metabolic work, converting ketamine into a breakdown product called norketamine, which itself may have some therapeutic activity.
Side Effects During and After Treatment
The most common side effects during an infusion are dissociation (feeling detached from your body or surroundings), dizziness, nausea, and temporary increases in blood pressure and heart rate. These effects typically resolve within an hour or two after the infusion ends. Some people experience vivid or strange perceptual changes, which can be unsettling but are expected at therapeutic doses.
The psychiatric safety profile is more nuanced. The American College of Emergency Physicians lists psychiatric illness as an absolute contraindication for dissociative sedation with ketamine, though this guideline was designed for emergency department procedural sedation, not for the low-dose infusions used in depression treatment. Some older concerns about ketamine raising pressure inside the skull or worsening high blood pressure have been largely debunked through more careful analysis, but clinicians still screen patients carefully before treatment.
Racemic Ketamine vs. Esketamine (Spravato)
In 2019, the FDA approved esketamine, sold as Spravato, a nasal spray containing only the S-enantiomer of ketamine, for treatment-resistant depression. This made it the first ketamine-derived drug officially approved for a psychiatric condition. The distinction between racemic ketamine and esketamine is one of the most important things to understand in this space.
S-ketamine binds to NMDA receptors with roughly four times the strength of R-ketamine, which is why it was initially seen as the more potent and promising molecule. But stronger receptor binding hasn’t translated into better clinical outcomes. A meta-analysis of 24 randomized controlled trials found that intravenous racemic ketamine was more effective than esketamine for major depression, with significantly higher response and remission rates and fewer people dropping out due to side effects.
A large population-based study reinforced these findings. After matching patients on key characteristics, those who started esketamine had a 24% higher risk of suicidal ideation compared to those who received injectable racemic ketamine. The study’s conclusion was straightforward: injectable racemic ketamine demonstrated a more favorable safety and effectiveness profile than esketamine. Racemic ketamine also appears to have a faster onset of antidepressant effects, likely due to differences in how the two formulations are absorbed and distributed in the body.
So why is esketamine the one with FDA approval? Largely because Janssen Pharmaceuticals invested in the clinical trials required for approval. Racemic ketamine has been a generic drug for decades, which means there’s little financial incentive for any company to fund the expensive trials needed to get it approved for depression. The result is an unusual situation where the version with stronger clinical evidence remains off-label while the version with a patent holds the official approval.
The Role of R-Ketamine
Growing interest in the R-enantiomer adds another layer to this picture. While S-ketamine is the stronger NMDA blocker, R-ketamine may produce longer-lasting antidepressant effects with fewer dissociative side effects. This has led some researchers to argue that the racemic mixture’s effectiveness comes not just from the S-enantiomer doing the heavy lifting, but from R-ketamine contributing complementary therapeutic activity through different pathways. Clinical trials of R-ketamine alone are underway, and early results have generated considerable excitement in the field.