A single ketamine infusion can reduce depression symptoms within hours, but the relief typically fades within about seven days. That fast but short-lived effect is what drives the repeated dosing schedules used in clinical practice, where patients receive multiple sessions over weeks to build and sustain improvement. How long the benefits last depends on the form of ketamine, the treatment protocol, and whether you’re receiving ongoing maintenance sessions.
How Quickly Ketamine Works
Traditional antidepressants like SSRIs take two to four weeks before patients notice any change in mood. Ketamine works on an entirely different timeline. Mood improvements can appear within hours of a single dose, with antidepressant effects measurable by about two hours after an infusion. This speed is what makes ketamine valuable for people with severe, treatment-resistant depression or acute suicidal thoughts.
The reason for this rapid effect lies in what ketamine does to brain cells. Rather than slowly adjusting serotonin levels the way SSRIs do, ketamine triggers a burst of new connections between neurons in the prefrontal cortex, the brain region involved in mood regulation and decision-making. Depression causes these connections to wither. Ketamine rapidly reverses that damage, increasing both the number and function of synaptic connections. This structural repair begins while the drug is still in your system and persists after it’s been cleared from your body.
Duration After a Single Dose
After one infusion, the antidepressant effect generally lasts about seven days. Some of the earliest clinical research on ketamine for depression, published in Biological Psychiatry, found that a single dose produced effects lasting up to three days. Later studies extended that estimate to roughly a week, though individual experiences vary. By the end of that window, symptoms typically return to their previous levels if no further treatment is given.
This is the core limitation of ketamine as a one-time treatment. The new neural connections it creates don’t appear to be permanent without reinforcement, so the mood benefits follow the same pattern. That’s why virtually all clinical protocols involve repeated sessions rather than a single infusion.
What a Typical Treatment Schedule Looks Like
Ketamine treatment for depression is structured in phases designed to build on that initial response. For intravenous (IV) ketamine, a common protocol involves an induction phase of twice-weekly infusions over four weeks. This series of sessions helps deepen and stabilize the antidepressant effect beyond what a single dose can achieve.
The FDA-approved nasal spray form, esketamine (sold as Spravato), follows a similar but more clearly defined schedule. For treatment-resistant depression, patients receive doses twice per week during the first four weeks. From weeks five through eight, the frequency drops to once weekly. After week nine, sessions are spaced to every two weeks, or once weekly if needed. The goal is to find the least frequent dosing schedule that maintains your improvement.
For people with major depression and acute suicidal thoughts, the Spravato protocol is more intensive: twice-weekly sessions at a higher dose for four weeks, after which the care team evaluates whether continued treatment is warranted.
IV Ketamine vs. Nasal Spray
The two main forms of ketamine used for depression don’t appear to be identical in effectiveness. IV ketamine uses a mixture of both molecular forms of the drug, while the nasal spray (Spravato) contains only one form, called esketamine. A meta-analysis comparing the two found that IV ketamine reduced depressive symptoms more effectively and sustained that improvement longer than the nasal spray. It also caused fewer side effects that led patients to stop treatment.
That said, a smaller head-to-head study found similar results between the two approaches. The practical differences matter too. Spravato is FDA-approved and covered by some insurance plans, while IV ketamine is used off-label for depression and often paid out of pocket. Both must be administered in a clinical setting where you’re monitored for at least two hours afterward.
How Long Benefits Last With Ongoing Treatment
With repeated sessions, many patients experience a cumulative effect where the relief between treatments becomes more stable. The induction phase (those first four weeks of frequent sessions) is designed to get you to that point. Once you’ve responded well, maintenance sessions keep the benefits going at longer intervals.
The maintenance phase is open-ended. Some people continue with sessions every two weeks for months or longer. Others find they can space treatments further apart over time. The Spravato prescribing guidelines explicitly recommend individualizing the schedule to the lowest frequency that preserves your response. There’s no standard endpoint where treatment is “complete,” and stopping maintenance sessions often leads to a return of symptoms, though the timeline varies from person to person.
Factors That Affect How Long It Lasts
Not everyone responds to ketamine for the same duration, and researchers have identified some variables that influence outcomes. People with unipolar depression (major depressive disorder without manic episodes) tend to respond better than those with bipolar depression. Whether your depression is classified as treatment-resistant, meaning it hasn’t improved with multiple standard antidepressants, also plays a role in how well and how long ketamine works, though the relationship is complex since treatment-resistant cases are precisely the population ketamine is most often used for.
Age, sex, and the severity of your depression before treatment may also influence results, though the data on these factors is less clear-cut. What is consistent across studies is that a single dose is not enough for lasting relief, and the best outcomes come from completing a full induction series followed by maintenance sessions tailored to your response.