Ketamine therapy is effective for depression, particularly when other treatments have failed. In controlled studies, about 71% of patients with treatment-resistant depression met response criteria the day after a single infusion, and 29% achieved full remission. These numbers are striking compared to traditional antidepressants, which can take weeks to show any effect and fail entirely for roughly a third of patients.
How Quickly It Works
The speed of ketamine’s antidepressant effect is what first drew researchers’ attention. Symptom relief typically begins about four hours after an intravenous infusion, well after the drug itself has cleared the bloodstream. This suggests the mood improvement isn’t a direct effect of ketamine being in your system but rather a downstream response, something the drug sets in motion that continues after it’s gone.
A single dose generally holds its effect for one to two weeks before depressive symptoms start returning to baseline. That window is both the promise and the limitation of ketamine therapy: it works fast, but it doesn’t last on its own.
Why It Works Differently Than Antidepressants
Traditional antidepressants target serotonin or norepinephrine and take weeks to produce changes. Ketamine works through an entirely different pathway. It blocks certain receptors on inhibitory brain cells, which releases the brakes on excitatory signaling in areas involved in mood regulation, particularly the prefrontal cortex and hippocampus. The result is a burst of activity that strengthens connections between neurons, essentially helping the brain rebuild communication pathways that depression has weakened.
This process of strengthening synapses is thought to be the reason ketamine’s effects outlast the drug’s presence in the body. The brain physically rewires in response to the initial burst of activity, and those structural changes persist for days to weeks after the infusion.
Rapid Reduction in Suicidal Thoughts
One of the most clinically significant findings involves suicidal ideation. A meta-analysis of individual patient data found that a single ketamine infusion reduced suicidal thoughts within 24 hours, with moderate to large effect sizes that persisted through one week. About 55% of patients were free of suicidal ideation the day after a single infusion, and 60% remained free at one week. No other available treatment reduces suicidal thinking this quickly, which makes ketamine particularly valuable in acute psychiatric crises.
What a Typical Treatment Schedule Looks Like
Because a single infusion’s effects fade within one to two weeks, most clinics use a loading phase followed by maintenance. A common initial protocol involves three infusions over the first week (every other day), then one infusion a week later, then infusions every two weeks going forward. Some protocols use two to three weekly infusions during the first month before spacing them out. An infusion every two weeks appears to be enough to maintain the initial response for many patients.
The goal is to find the longest interval between treatments that still keeps symptoms at bay. Some people eventually stretch to monthly infusions; others need them more frequently.
IV Ketamine vs. Nasal Spray (Spravato)
There are two main delivery methods. Intravenous ketamine (the original, used off-label) and esketamine nasal spray (brand name Spravato, the only FDA-approved form for depression). Both work, but they aren’t identical in practice.
A 2024 meta-analysis comparing the two found that IV ketamine and nasal esketamine produce similar overall response and remission rates, with a slight, non-significant edge for IV ketamine. Where the difference becomes more meaningful is speed. In one detailed comparison, the median number of treatments to achieve response was 2 for IV ketamine versus 4 for the nasal spray. Time to remission was also significantly shorter with IV ketamine. One study found that 47% of IV ketamine patients responded by week one, compared to just 7% of those using intranasal esketamine.
The tradeoff: Spravato is FDA-approved, which means insurance is more likely to cover it, and it comes with standardized safety monitoring. IV ketamine is administered off-label, often at specialized clinics, and typically costs $400 to $800 per session out of pocket.
Side Effects During Treatment
Ketamine’s side effects are real but generally short-lived, resolving within a couple of hours after infusion. The most common experiences feel unusual rather than dangerous: feeling strange or spacey, floating sensations, visual distortions, difficulty speaking, and numbness. Dissociation, a sense of detachment from your body or surroundings, occurs in about 62% of patients (compared to 2% with placebo). Temporary blood pressure elevation happens in about 19% of patients, and nausea in about 16%.
These effects are why ketamine is administered in a clinical setting with monitoring. Most clinics require you to stay for at least two hours after an infusion and arrange a ride home.
Ketamine for Chronic Pain
Beyond depression, ketamine is used for certain chronic pain conditions, particularly neuropathic pain. It has been studied in complex regional pain syndrome (CRPS), phantom limb pain, postherpetic neuralgia, fibromyalgia, and other nerve-related pain conditions. CRPS patients tend to show the strongest response.
Pain protocols differ significantly from depression protocols. Infusions are often longer (up to four hours per session) and may run daily for up to five days, or two to three times per week for one to two weeks. Longer infusion durations generally produce longer-lasting pain relief. If there’s no meaningful improvement after this initial trial, ketamine for pain is typically discontinued. The intravenous route consistently outperforms other delivery methods (oral, topical, intranasal) for pain management.
Who Responds Best
Not everyone benefits equally from ketamine, and researchers have identified some patterns in who tends to respond well. Patients with a family history of alcohol use disorder in a first-degree relative show greater improvement at both one day and one week after treatment. People who have poorer baseline cognitive performance, particularly slower processing speed, also tend to respond better. And blood levels of a specific amino acid (d-serine) are notably lower in responders compared to non-responders before treatment begins.
These findings are still being refined and aren’t yet used to screen patients in most clinical settings. In practice, the strongest predictor remains the simplest one: ketamine tends to work best in people whose depression hasn’t responded to conventional treatments, the exact population that needs new options most.