Ketamine treatment works by triggering a rapid burst of new neural connections in the brain, producing antidepressant effects within hours rather than the weeks required by traditional antidepressants. It does this through a fundamentally different mechanism than standard medications, which is why it can help people whose depression hasn’t responded to other treatments. Here’s what happens in your brain, what the treatment looks like in practice, and what to realistically expect.
What Ketamine Does in the Brain
Most antidepressants work by adjusting levels of serotonin or similar chemical messengers, a process that takes weeks to produce noticeable changes. Ketamine takes a different route entirely. It blocks a specific receptor involved in signaling between brain cells, which sets off a cascade that rapidly promotes the growth of new connections between neurons, particularly in the prefrontal cortex, the region responsible for mood regulation, decision-making, and emotional processing.
Depression is associated with a loss of these neural connections. Brain imaging and tissue studies show that people with chronic depression have fewer and weaker synaptic connections in the prefrontal cortex. Ketamine essentially kickstarts a repair process. Within hours of a dose, the brain begins forming new dendritic spines, the tiny structures on neurons that receive signals from other cells. This burst of new spine growth happens before overall connection density measurably increases, suggesting that the brain’s rewiring process begins almost immediately.
This process also depends on dopamine. Research published in Biological Psychiatry found that ketamine enhances spine growth through activation of dopamine receptors in the prefrontal cortex. When researchers blocked dopamine release, ketamine’s behavioral effects disappeared. When they activated those same dopamine pathways independently, they could mimic ketamine’s antidepressant action. This dopamine-dependent plasticity helps explain why the effects feel different from a typical antidepressant and why onset is so much faster.
How Quickly It Works and How Long It Lasts
The speed is the headline feature. While conventional antidepressants typically take four to six weeks to reach full effect, ketamine can reduce depressive symptoms within hours of the first treatment. This makes it particularly valuable for people in acute crisis or those who haven’t responded to other medications.
The catch is durability. In most patients who respond well to a single dose, the benefits fade within about two weeks. Even with repeated dosing, the median time to relapse after stopping treatment is only two to three weeks. This means ketamine is not a one-and-done fix. It requires ongoing maintenance to sustain its effects, and it works best as part of a broader treatment plan that includes oral antidepressants, therapy, or both.
What a Treatment Session Looks Like
Ketamine for depression is administered in a clinical setting under direct supervision. The most common protocol uses an IV infusion at a dose of 0.5 mg/kg of body weight, delivered over about 40 minutes. Some patients respond to lower doses (as low as 0.1 mg/kg), while others need up to 0.75 mg/kg. There is also an FDA-approved nasal spray form called Spravato (esketamine), which is a close chemical relative of ketamine.
A typical induction phase involves six infusions, usually given on alternating days over two to three weeks. In one study of patients with treatment-resistant depression, only 7% responded after the first three infusions, but 42% responded after completing all six. This suggests that people who don’t feel much after the first session or two shouldn’t necessarily give up on the treatment.
During the infusion, you stay in a reclining chair while medical staff monitor your blood pressure, heart rate, and oxygen levels. The experience itself is distinctly different from taking a pill at home. Ketamine produces a dissociative state, meaning your perception of your body and surroundings can feel altered. You might feel detached, experience unusual visual or sensory perceptions, or feel a floating sensation. These effects typically peak around 40 minutes into the session and wear off within two hours. You won’t be able to drive yourself home afterward.
FDA-Approved vs. Off-Label Use
There’s an important distinction between the two forms of ketamine used for depression. Spravato (esketamine nasal spray) is FDA-approved for two specific conditions in adults: treatment-resistant depression, defined as depression that hasn’t improved after trying at least two different antidepressants, and major depressive disorder with acute suicidal ideation or behavior. It must be used alongside an oral antidepressant, not on its own. It is not approved for anyone under 18.
Racemic ketamine, the original form given by IV, is not FDA-approved for depression. It is legally used off-label, meaning doctors prescribe it based on clinical evidence even though it hasn’t gone through the formal approval process for this specific purpose. This distinction matters because insurance coverage, clinic protocols, and regulatory oversight differ between the two. Spravato must be administered through a certified healthcare facility enrolled in a restricted program, while IV ketamine clinics operate with more variability in standards.
Side Effects During Treatment
The most common side effects are dissociation, nausea, headache, and anxiety. These are typically short-lived, resolving within two hours of treatment.
Blood pressure elevation is the side effect that gets the most clinical attention. Ketamine stimulates the cardiovascular system, increasing heart rate and blood pressure temporarily. In studies, systolic and diastolic blood pressure peak about 40 minutes into the infusion, rising an average of 16 and 11 points respectively. Between 10% and 50% of patients experience a noticeable blood pressure increase during infusion, and roughly 12.5% experience a more severe spike. These surges are more common during the first three infusions and in older patients or those with a history of high blood pressure. In most cases the spike is transient, but some patients need medication during the session to bring it down.
Who Should Not Receive Ketamine
Several conditions rule out ketamine treatment. According to the American Psychiatric Nurses Association, the standard exclusion list includes active substance abuse (alcohol, cannabis, or non-prescribed drugs), a history of psychosis, increased intracranial pressure, current pregnancy, uncontrolled high blood pressure, acute or unstable heart disease, and a previous bad reaction to ketamine. The FDA-approved nasal spray carries additional contraindications for anyone with a cerebral aneurysm, history of bleeding in the brain, or certain blood vessel malformations.
Maintenance and Long-Term Expectations
After the initial induction phase, most patients who respond well transition to maintenance sessions at gradually increasing intervals. There is no single established protocol for this. Some patients do well with infusions every two to four weeks, while others need them more frequently. The research base for long-term maintenance is still limited, and no definitive trials have compared different maintenance schedules head-to-head.
What is clear is that stopping treatment usually leads to relapse within weeks. This positions ketamine more like an ongoing therapy than a cure. The goal for most treatment plans is to use the rapid relief ketamine provides as a bridge, stabilizing mood quickly while longer-term treatments like oral medications and psychotherapy take hold. Some patients stay on periodic maintenance infusions indefinitely, while others are able to taper off as other treatments become effective.
Cost is a practical consideration. IV ketamine is rarely covered by insurance because it’s off-label for depression. Spravato has broader insurance coverage but still involves copays and the time commitment of in-clinic administration with a mandatory observation period. A single IV infusion typically costs between $400 and $800 out of pocket, and a full induction course of six sessions adds up quickly.