Ketamine treats several conditions, most notably treatment-resistant depression, acute suicidal thoughts, chronic pain, and PTSD. It is also FDA-approved as a general anesthetic. While it has been used in operating rooms since the 1960s, ketamine’s rapid-acting antidepressant properties have made it one of the most significant developments in psychiatric treatment in decades.
Treatment-Resistant Depression
Depression that hasn’t responded to two or more standard antidepressants is classified as treatment-resistant, and this is where ketamine has shown its most dramatic results. In clinical studies, about 48% of patients with treatment-resistant depression responded to a single ketamine infusion within three days, and 34% achieved full remission in that same window. Those numbers are striking for a population that, by definition, has already failed multiple medications.
Traditional antidepressants typically take four to six weeks to show effects. Ketamine works on a completely different system in the brain. Rather than targeting serotonin or norepinephrine, it blocks a receptor involved in how brain cells communicate through glutamate, the brain’s primary excitatory chemical messenger. This triggers a cascade that promotes the growth of new connections between neurons, particularly in the prefrontal cortex and hippocampus, two regions that physically shrink under chronic stress and depression. In essence, ketamine helps rebuild the wiring that depression has degraded.
A nasal spray form called esketamine (brand name Spravato) received FDA approval in 2019 specifically for treatment-resistant depression. It uses a slightly different version of the ketamine molecule and is administered in a certified clinic under medical supervision. Intravenous ketamine, the older and more widely studied form, achieves similar response and remission rates but appears to get patients to remission in fewer treatment sessions. One observational study found that IV ketamine reached remission about five times faster than the nasal spray when measured by number of treatments needed.
Acute Suicidal Ideation
Perhaps ketamine’s most urgent application is reducing suicidal thoughts. A meta-analysis pooling data from eight studies found that a single infusion significantly reduced suicidal ideation within 24 hours, with moderate-to-large effect sizes. More than half the patients experienced meaningful reductions in suicidal thinking within that first day, and the benefits persisted for up to one week.
This speed matters enormously. No other widely available psychiatric medication works this fast against suicidal thoughts. Standard antidepressants take weeks, and some carry black-box warnings about temporarily increasing suicidal ideation in younger patients during the initial adjustment period. Ketamine fills a critical gap in emergency and acute psychiatric care, offering a bridge that can keep patients safe while longer-term treatments take hold. The nasal spray formulation also carries an FDA-approved indication for depressive symptoms with suicidal ideation or behavior.
Post-Traumatic Stress Disorder
Ketamine is showing real promise for PTSD, though it hasn’t yet received FDA approval for this use. A recent open-label trial combined ketamine infusions with a structured form of trauma-focused therapy in patients with severe, chronic PTSD. After 12 weeks, average symptom severity scores dropped by roughly half, from 41.6 to 20.8 on a standard clinical scale. Sixty-nine percent of patients qualified as treatment responders, and about 62% maintained their improvement at a six-month follow-up.
The thinking behind this combination approach is that ketamine’s ability to promote new neural connections may open a window of heightened brain plasticity. During that window, therapeutic work on traumatic memories may be more effective, allowing the brain to form new, less distressing associations with those memories. This is still an emerging area, but the early results suggest ketamine could become an important tool for PTSD that hasn’t responded to conventional treatments.
Chronic Pain
Ketamine has a well-established role in managing certain chronic pain conditions, particularly complex regional pain syndrome (CRPS). CRPS causes intense, burning pain usually in a limb, often after an injury, and it can be extraordinarily difficult to treat. Ketamine infusions work by interrupting pain signaling pathways in the nervous system, specifically blocking the same receptors involved in a phenomenon called central sensitization, where the nervous system essentially gets stuck in a high-alert state and amplifies pain signals.
Treatment protocols for chronic pain vary widely. Infusions for CRPS have been studied at doses ranging from low (comparable to sub-anesthetic psychiatric doses) all the way up to much higher anesthetic-level doses administered over multiple days in an intensive care setting. The lower-dose outpatient approach is more common and carries fewer risks. Beyond CRPS, ketamine infusions are also used for other chronic pain conditions including fibromyalgia, neuropathic pain, and certain types of cancer-related pain, though the strength of evidence varies across these conditions.
Bipolar Depression
Ketamine’s role in bipolar depression is more nuanced. The core concern is whether it might trigger a manic or hypomanic episode, which would be dangerous. A scoping review of 10 clinical studies found that ketamine appeared tolerable with minimal risk of manic switching and showed some effectiveness for both depressive symptoms and suicidality in bipolar patients. However, the overall evidence remains limited, and most of the landmark ketamine-for-depression studies specifically enrolled patients with unipolar depression. If you have bipolar disorder, ketamine treatment requires careful screening and monitoring that accounts for this added complexity.
Anesthesia
Ketamine’s original and still-current FDA approval is as an anesthetic. It is classified as a Schedule III controlled substance and is used for induction and maintenance of general anesthesia. What makes it unusual among anesthetics is that it maintains breathing reflexes and blood pressure better than most alternatives. This makes it particularly valuable in emergency medicine, battlefield settings, pediatric procedures, and situations where patients have unstable cardiovascular systems. It remains one of the World Health Organization’s essential medicines for this reason.
How Treatment Typically Works
For psychiatric uses, ketamine is most commonly given as a slow IV infusion over about 40 minutes in a clinical setting. You sit in a reclining chair, often with dimmed lights and sometimes music. The experience itself can include feelings of floating, mild dissociation, or altered perception. These effects typically fade within one to two hours after the infusion ends. Most clinics monitor you for about two hours total before you go home with a driver.
The nasal spray version follows a similar supervised model. You self-administer the spray in a certified healthcare setting and are monitored for at least two hours afterward due to potential sedation and dissociation. You cannot drive for the rest of the day.
For depression, an initial course often involves multiple sessions over two to three weeks, followed by less frequent maintenance sessions as needed. The effects of a single treatment tend to fade within days to a couple of weeks, which is why repeated sessions are standard. One of the ongoing challenges with ketamine treatment is sustaining its benefits over time, and combining it with psychotherapy or other medications is a common strategy to extend its effects.
Common Side Effects
Short-term side effects during or shortly after treatment typically include dizziness, nausea, increased blood pressure, and dissociation, a feeling of detachment from your body or surroundings. These generally resolve within a couple of hours. Some people find the dissociative experience unpleasant, while others describe it as neutral or even therapeutic.
With repeated use over longer periods, there are additional concerns. Frequent ketamine exposure has been associated with bladder problems, including inflammation that can cause urinary urgency, frequency, and pain. This has been documented more extensively in people who use ketamine recreationally at high doses, but clinicians monitoring therapeutic use watch for early urinary symptoms as well. Cognitive effects with long-term use are another area of active study, and the lack of long-term safety data for repeated psychiatric dosing is one reason treatment is delivered in supervised clinical settings rather than prescribed for home use (with some exceptions for the nasal spray and certain oral formulations under specific protocols).