Long-Term Effects of Ketamine Therapy

Some patients continue ketamine or Spravato treatment for months or years, usually as maintenance treatment after an initial response. Maintenance dosing is normal, not a sign something has gone wrong. The evidence supporting those long stretches is real, and it's also uneven in a way worth understanding before you commit to it.

The clearest picture comes from Spravato, which has been followed in a formal extension study for up to six and a half years. Repeated off-label IV or IM ketamine has a thinner long-term record, built more from smaller studies and clinical experience than from large multi-year trials.

One more distinction runs through everything below. What we know about heavy nonmedical ketamine use, which is where many of the most serious long-term harms have been documented, does not automatically describe someone receiving supervised treatment every few weeks. That said, no known harm is not the same as proven safe, and the honest answer to several questions here is that nobody knows yet.

What Counts as Long-Term Ketamine Treatment?

"Long-term" gets used for wildly different timeframes. A study calling itself long-term might mean eight weeks, a year, or several years, so the word tells you very little on its own.

Treatment itself usually falls into three phases. The induction series is the initial run of closely spaced sessions, often a few weeks. Continuation covers the period right after, where treatment keeps the gains from slipping. Maintenance is ongoing treatment at longer intervals, sometimes lasting years.

When you read that long-term treatment is safe, ask how long, in how many people, and measuring what. A four-week follow-up and a four-year follow-up are both technically long-term.

How Much Long-Term Evidence Do We Actually Have?

The amount varies enormously by treatment type.

Spravato has the strongest record. SUSTAIN-3, a phase 3 extension study, followed 1,148 adults with treatment-resistant depression for a mean of about 43 months, with some past six years and nearly two-thirds continuing at least three years. That adds up to roughly 3,777 patient-years of exposure, and the final analysis found no new safety signals compared with shorter studies.

That design matters as much as the numbers. SUSTAIN-3 was open-label and single-arm, with no long-term randomized comparison group, and participants entered from earlier esketamine studies. People who tolerate a treatment and benefit from it are likelier to stay in an extension study. So it is powerful evidence about what happens across years of exposure, and it cannot prove that any particular outcome was caused or prevented by esketamine.

Two earlier studies support it: SUSTAIN-1 tested relapse prevention, and SUSTAIN-2 followed safety across a year.

Repeated IV and IM ketamine has less. A systematic review of maintenance ketamine treatment found three randomized controlled trials, eight open-label trials, and about thirty case series and case reports. That's a real evidence base, though not thousands of patient-years under one protocol. Its authors concluded that tachyphylaxis, cognitive impairment, addiction, and serious renal or urinary problems all appear uncommon.

Neither picture comes from studies designed to detect rare harms over decades.

Can Ketamine Keep Working Over Time?

Yes, for a substantial share of people, as long as treatment continues.

In SUSTAIN-3, the improvement people gained during the initial four weeks generally persisted through maintenance. Just under half of assessed participants were in remission at their maintenance endpoint, with a similar proportion meeting a functional measure covering work and daily life. Those are descriptive figures from a cohort that stayed in the study, measured at varying timepoints, rather than the odds any individual will be in remission years from now. Discontinuation for insufficient effect ran at about 5 percent.

The maintenance ketamine review reached a similar conclusion for other routes, finding that maintenance dosing sustained antidepressant effect. What none of this shows is that maintenance works indefinitely for everyone. Some people need their interval adjusted over time, and some stop responding and move to something else.

Two ideas here sound alike. Sustained response while treatment continues is well documented. A durable cure that persists after treatment ends is a different claim, and much weaker.

What Happens When Maintenance Treatment Stops?

Depression often returns. SUSTAIN-1 was built to test exactly this, in patients already stabilized on esketamine plus an oral antidepressant. Those who had reached stable remission had a 51 percent lower relapse risk when they continued esketamine, rather than switching it to placebo while staying on the oral antidepressant. Among stable responders who had not reached remission, the reduction was 70 percent.

That's a meaningful finding, and it isn't a promise. Some people taper off maintenance and stay well. Others find symptoms creeping back within weeks, which says something about the illness rather than the person.

Returning symptoms are also not withdrawal. Recurrence of depression and physical dependence are different phenomena, and our guide on whether ketamine can be addictive works through why they get confused.

Does Ketamine Stop Working Because of Tolerance?

Both prescribing labels report tolerance with prolonged use. Most of that evidence comes from anesthesia and heavy repeated exposure, where higher doses become needed for the same effect.

Whether the antidepressant benefit specifically wears off is a separate question, and it's poorly studied. The maintenance review found tachyphylaxis appeared uncommon, but few studies were designed to detect it. Tolerance to dissociative effects doesn't prove tolerance to therapeutic benefit, and those effects are mediated differently.

If treatment seems to be losing effect, that's a conversation with your provider.

Long-Term Effects on Memory and Thinking

This worry comes up constantly, because heavy recreational ketamine use is associated with problems in memory and attention. That research describes a very different exposure pattern than supervised treatment.

Within psychiatric treatment, the picture looks reassuring so far. SUSTAIN-3 assessed cognition across multiple domains and found it remained stable, without clinically meaningful change over years, in both younger and older participants. A minor slowing in reaction time appeared, and the researchers described its clinical relevance as unclear.

Two caveats keep that from being the last word. The study was open-label with no comparison group, and depression itself impairs concentration and memory, so improvement in mood can make cognition look better independently of the drug. Persistent cognitive complaints during treatment are worth raising rather than accepting.

Can Long-Term Ketamine Affect the Bladder or Urinary Tract?

Ketamine-associated bladder injury is well established with frequent nonmedical use. Ketamine injection labeling describes cystitis, reduced bladder capacity, ureteral stenosis, and hydronephrosis with long-term use or abuse.

Therapeutic treatment data look different. SUSTAIN-3 recorded urinary adverse events including dysuria, cystitis, and urinary frequency, each in roughly 2 to 3 percent of participants. Those are events observed during treatment rather than problems shown to be caused by it. Across nearly 3,800 patient-years, no case of treatment-related interstitial or ulcerative cystitis was reported. A 2025 systematic review of psychiatric ketamine studies found reported urinary symptoms ranging from zero to 24.5 percent across studies. That is not an incidence rate caused by treatment, since studies measured differently and control groups sometimes reported similar rates.

Many studies tracked urinary health for weeks rather than years. Report new urinary frequency, urgency, pain, or blood in the urine promptly so your team can evaluate it. Our guide on ketamine therapy side effects covers the shorter-term picture.

Liver and Bile-Duct Effects With Repeated Treatment

Ketamine can affect the liver and bile ducts, and where that shows up matters. The serious presentations, including cholangiopathy with bile duct stricturing, cluster in chronic heavy nonmedical use over months to years, and in prolonged high-dose infusion such as continuous sedation. Repeated high-dose infusion protocols for chronic pain have also produced drug-induced liver injury in reported cases.

Standard psychiatric dosing is a lower exposure than any of those. In SUSTAIN-3, fewer than one in ten participants had a hepatic adverse event recorded. Reported events included elevated GGT, ALT, or AST, as well as other liver or biliary findings. These events did not become more common over time, and few participants stopped treatment because of them. Recorded adverse events are not the same as harm caused by Spravato.

Routine liver testing isn't universally required for psychiatric ketamine treatment. Clinicians may consider it based on treatment frequency and cumulative exposure, symptoms like abdominal pain or jaundice, existing liver disease, and other medications, which our guide on ketamine and other medications discusses.

Blood Pressure and Cardiovascular Effects Over Time

Ketamine reliably raises blood pressure during a session. The real long-term question is whether repeating that hundreds of times causes cumulative harm.

The available data don't show that, though they also weren't designed to settle it. In SUSTAIN-3, blood pressure rose about 8 to 10 points on average, peaked around 40 minutes after dosing, and generally returned to predose values by about 90 minutes. Markedly elevated readings occurred in 6.5 percent of participants at some point. The rate of blood pressure adverse events stayed broadly similar across visits, so no worsening pattern appeared during the study.

What's missing is cardiovascular outcome data. No study has tracked heart attacks or strokes across decades of maintenance treatment, so this is an area where absence of a signal is genuinely different from proof of safety. Our guide on whether ketamine therapy is safe covers how sessions are monitored.

Does Long-Term Treatment Increase Addiction or Dependence Risk?

Ketamine has real abuse potential, and longer exposure makes ongoing monitoring more important rather than less.

The long-term Spravato data have not identified a trend suggesting abuse, misuse, or withdrawal within its supervised delivery model. That's reassuring, and it's bounded: participants were treated in certified settings under observation, which is exactly the arrangement designed to prevent those outcomes. It doesn't establish zero risk, particularly outside that structure.

Our guide on whether ketamine can be addictive covers dependence, tolerance, and misuse in full.

Are Long-Term Risks Different for Spravato and IV Ketamine?

The honest answer is that the evidence differs more than the risks are known to.

Spravato is a standardized product with FDA-approved psychiatric indications, given on a defined schedule inside a REMS framework and studied with multi-year follow-up. Off-label IV and IM ketamine has no FDA-defined psychiatric protocol, so dose, route, frequency, and monitoring vary between clinics, and the long-term datasets are smaller.

That's a statement about what has been measured, not a ranking. Our guide comparing IV ketamine and Spravato covers the practical differences.

What About Repeated At-Home Ketamine?

Long-term at-home ketamine raises different questions because treatment happens outside a clinic. Route, dose, and frequency often differ from in-person protocols, and monitoring practices vary between providers.

High-quality long-term evidence for this model is limited. That's a gap in the research rather than a finding of harm, and it isn't a basis for calling at-home treatment unsafe. It does mean anyone in long-term at-home treatment is relying more heavily on their prescriber's monitoring practices.

How Often Do Patients Receive Maintenance Treatment?

Intervals vary, and there's no universal schedule.

Spravato's labeling is specific for treatment-resistant depression. Induction is twice weekly for four weeks. Weeks five through eight are once weekly. From week nine onward, dosing is once weekly or every two weeks, individualized to the least frequent dosing that maintains response or remission. The label also directs clinicians to evaluate evidence of benefit at the end of induction before continuing.

One clarification worth making: SUSTAIN-3 allowed some participants to dose every four weeks under its research protocol. That interval is not part of the current labeled maintenance schedule, and research protocols aren't prescribing instructions.

Off-label IV and IM ketamine has no FDA-defined psychiatric schedule. Maintenance intervals are set individually and can range from every couple of weeks to considerably less often. What's right for you is a clinical decision, not something to calibrate from an article.

How Do Clinicians Monitor Long-Term Ketamine Treatment?

Good long-term care tracks whether treatment is still earning its place: whether symptoms keep improving, whether daily functioning improves, and how long benefit lasts between sessions.

On the medical side, blood pressure is checked around each treatment. Beyond that, monitoring should match your situation: urinary symptoms, liver-related symptoms or labs when clinically appropriate, cognitive concerns if they arise, medication changes, and any substance use concerns.

Clinics differ in how formally they do this, and no single lab panel is standard across psychiatric ketamine treatment. What matters is that someone is actively looking rather than repeating sessions by default.

When Should Long-Term Treatment Be Reconsidered?

Several situations are worth raising with your clinician rather than pushing through:

Benefit has become hard to identify
Treatment frequency keeps increasing without clear improvement
Side effects persist or become troublesome
New urinary symptoms appear
Liver-related symptoms or abnormal results show up
Blood pressure becomes harder to manage
Cognitive complaints develop and don't resolve
Concerns about misuse emerge
The burden of treatment starts outweighing what you get from it

None of these means stopping on your own. They're reasons to review the plan with the person managing it.

What We Still Don't Know

The gaps are specific.

Nobody has followed psychiatric ketamine patients for decades, so the outer boundary of what's known is roughly six years. Long-term standardized data for off-label IV and IM protocols remain limited compared with Spravato. The best maintenance interval is unsettled, and so is which patients can successfully taper off and stay well.

There's no reliable way to predict who will still be responding in three years. Long-term bladder risk at psychiatric exposure levels hasn't been followed long enough, and the same is true of subtle cognitive change.

Trial populations also aren't everyone. SUSTAIN-3 excluded people with significant psychiatric comorbidities, enrolled a mostly White population, and provided clinical support beyond what most real-world settings offer.

What Long-Term Treatment Looks Like in Practice

Ongoing ketamine treatment shouldn't run on autopilot. The strongest sign of a good long-term provider is that they keep asking whether continuing still makes sense.

Questions worth revisiting: Is this still helping in ways you can point to? How long does each treatment hold? Could the interval be stretched? Have new side effects appeared? Does the benefit still justify the time, cost, and exposure?

Our guide on how to choose a ketamine clinic covers what to look for. You can also search ketamine clinics near you, or browse Spravato treatment centers and IV ketamine infusion clinics.