Ketamine is a dissociative anesthetic, a drug that makes people feel detached from their pain and surroundings. Originally developed in the 1960s as a safer alternative to earlier anesthetics, it has been used in operating rooms and emergency departments for over 50 years. More recently, ketamine has gained attention for its rapid effects on severe depression and chronic pain, opening up uses that go well beyond its original purpose as a surgical drug.
How Ketamine Works in the Brain
Most anesthetics simply slow down brain activity across the board. Ketamine does something different. It blocks a specific type of receptor called the NMDA receptor, which normally responds to glutamate, the brain’s primary excitatory chemical messenger. By plugging into these receptors, ketamine prevents glutamate from activating them, creating that characteristic “dissociative” state where a person feels separated from their body and environment.
What makes ketamine especially interesting for depression treatment is where it acts first. It appears to preferentially block NMDA receptors on inhibitory brain cells, the ones whose job is to quiet down other neurons. When these inhibitory cells get suppressed, the net effect is a burst of activity in excitatory brain cells, particularly in areas of the prefrontal cortex involved in mood regulation. This surge triggers a cascade that promotes new connections between neurons, essentially helping the brain rewire circuits that depression may have weakened. Animal studies show that sub-anesthetic doses significantly increase glutamate levels in the prefrontal cortex, and this burst of signaling appears central to ketamine’s antidepressant effect.
Ketamine for Treatment-Resistant Depression
Standard antidepressants take weeks to start working and fail entirely for roughly a third of patients. Ketamine works on a completely different timeline. Effects can appear within 40 minutes of a single intravenous infusion, and response rates in clinical trials have ranged from 50% to 70% in patients with major depression. In one randomized controlled trial comparing ketamine to an active placebo, 64.8% of patients with treatment-resistant depression responded to ketamine versus 28% in the control group. Response here means at least a 50% reduction in depression severity scores.
The catch is durability. A single infusion typically provides relief lasting three to seven days, though some patients experience longer improvement. In studies using repeated infusions (up to six over two weeks), response rates reached about 71%, and responders stayed well for an average of 18 days after the final infusion. The antidepressant effect generally lasts somewhere between one week and one month, meaning most people need ongoing treatment sessions to maintain the benefit.
Ketamine also shows striking effects on suicidal thinking. In one study, 53% of patients who received ketamine had no suicidal thoughts at 24 hours, compared to 24% of those on placebo. Suicidal ideation scores improved by nearly 65% within 24 hours of a single infusion. For people in acute crisis, that speed matters enormously.
The FDA-Approved Nasal Spray
In 2019, the FDA approved esketamine (brand name Spravato), a nasal spray form of one of ketamine’s two mirror-image molecules. It is approved for two specific uses: treatment-resistant depression in adults, and depressive symptoms in adults with major depression who have acute suicidal ideation or behavior. In both cases, it is used alongside a standard oral antidepressant.
Spravato cannot be picked up at a pharmacy and taken at home. It is available only through a restricted program that requires you to take the spray at a certified healthcare setting, under direct observation, and remain for at least two hours of monitoring afterward. This restriction exists because of the risks of sedation, dissociation, and breathing changes that can occur shortly after a dose. In pilot trials of intranasal ketamine, 44% of patients with treatment-resistant depression responded, compared to 6% on placebo, with effects lasting about 48 hours.
Chronic Pain Treatment
At doses lower than those used for anesthesia, ketamine can relieve chronic pain, particularly nerve-related pain conditions. Because NMDA receptors play a key role in how the nervous system amplifies and sustains pain signals, blocking them can interrupt the cycle of chronic pain at its source. Ketamine has been studied in a wide range of conditions: complex regional pain syndrome, fibromyalgia, post-shingles nerve pain, spinal cord injury pain, phantom limb pain, chemotherapy-induced nerve damage, and chronic migraine, among others.
How long the pain relief lasts depends heavily on the treatment protocol. A single 30-minute infusion for fibromyalgia, for example, provided pain relief lasting only about 45 minutes. But longer infusion courses tell a different story. In patients with complex regional pain syndrome, a multi-day infusion protocol (about 100 hours total) produced pain relief lasting up to three months. A separate trial using four-hour daily infusions over 10 days showed similar extended benefits. The pattern is clear: longer or repeated treatments tend to produce more durable pain relief, though ketamine for chronic pain is generally reserved for patients who have not responded to standard therapies.
Side Effects and What to Expect
The most recognizable side effect of ketamine is dissociation, a feeling of being detached from your body or surroundings. In phase III clinical trials, 12.5% to 27.6% of patients reported dissociation, and fewer than 4% described it as severe. These symptoms peak around 40 minutes after administration and typically resolve within 90 minutes. In one study tracking 49 patients across multiple infusions, all dissociative symptoms dropped to “absent” within one hour of each infusion, with no lasting effects.
Other common short-term effects include dizziness, nausea, increased blood pressure, and a sense of unreality or unusual perceptions. Some people find the experience pleasant, others find it uncomfortable, but the effects are consistently short-lived. Importantly, dissociative symptoms tend to become less intense with repeated treatments, meaning the first session is usually the most noticeable.
Legal Status in the United States
Ketamine became a Schedule III controlled substance under the Controlled Substances Act in 1999. This classification means it has accepted medical uses but also a recognized potential for misuse. It sits in the same scheduling tier as drugs like testosterone and certain codeine preparations, lower than Schedule II drugs like oxycodone but still regulated. Ketamine is approved as an injectable anesthetic for both humans and animals, and clinicians can legally prescribe it off-label for depression and pain at their medical judgment, separate from the FDA-approved esketamine nasal spray.
The off-label landscape has led to a rapid expansion of ketamine clinics across the country, where intravenous or other forms of ketamine are administered for mood disorders and pain outside of the Spravato program. These clinics operate under standard medical practice rules rather than the restricted certification program required for esketamine, which means oversight, protocols, and patient monitoring can vary significantly from one clinic to the next.