Ketamine treatment is generally safe when administered in a medical setting with proper monitoring, but it comes with real side effects and risks that vary depending on the dose, frequency, and your individual health profile. The most common concerns during treatment are temporary increases in blood pressure, dissociation, and nausea. Serious adverse events are rare in supervised clinical settings, largely because most providers screen out high-risk patients before treatment begins.
What Happens in Your Body During Treatment
Ketamine works by blocking a specific receptor in the brain involved in signaling between nerve cells. This triggers a chain reaction: it temporarily quiets certain inhibitory brain cells, which allows excitatory signaling to increase. That burst of activity strengthens connections between neurons, which is thought to be the basis of its rapid antidepressant effects. Unlike traditional antidepressants that take weeks to work, these changes in brain connectivity can begin within hours.
This mechanism also explains why ketamine produces its distinctive side effects. The same surge in brain activity that helps with depression can cause feelings of disconnection from your body, altered perception, and a dreamlike state during the infusion.
Side Effects During and After Each Session
The most common side effects are dissociation, nausea, headache, anxiety, and a temporary spike in blood pressure. These typically begin during the infusion and resolve within a couple of hours.
Blood pressure increases are the side effect that clinicians monitor most closely. On average, systolic blood pressure rises by about 16 points and diastolic by about 11 points, peaking around 40 minutes after the infusion starts. In one study of 84 patients across 205 infusions, roughly 20 to 30 percent experienced blood pressure above 180/100 or a heart rate above 110 beats per minute, and 12 patients needed medication to bring their blood pressure down. These spikes are temporary, but they’re the main reason you’re monitored for at least two hours after each session.
Dissociation, the feeling of being detached from your body or surroundings, is extremely common and typically lasts 30 to 60 minutes. Some patients find it unsettling, while others describe it as neutral or even calming. It fades on its own and doesn’t require intervention.
Who Should Not Receive Ketamine
Most clinical trials and treatment centers screen for conditions that could make ketamine dangerous. People with uncontrolled high blood pressure, a history of aneurysm, or significant cardiovascular disease are typically excluded because of ketamine’s blood pressure effects. A history of psychosis or active psychotic symptoms is another common exclusion, since ketamine can worsen these conditions. Pregnant individuals are also not candidates.
A large systematic review found that 83 percent of published studies screened for medical illness and excluded high-risk patients before treatment. Across those studies, no serious cardiac events or deaths were reported. That’s an encouraging number, but it reflects the fact that the safety data we have comes mostly from carefully selected patients. If you have cardiovascular risk factors or a complex psychiatric history, your provider should weigh those risks individually.
Cognitive Effects Over Time
One of the most common concerns about repeated ketamine treatment is whether it harms memory or thinking ability. The clinical evidence so far is reassuring at the doses used for depression. A study of veterans who received six infusions over 12 days found no worsening on any measure of cognition. Working memory actually improved after the infusion series. Other studies have found similar patterns: improvements in processing speed and verbal learning, with no decline in autobiographical memory or recall.
Animal research and data from chronic recreational users paint a different picture, showing potential links to memory loss and neurodegeneration with heavy, prolonged exposure. The key difference is dose and frequency. Clinical treatment uses sub-anesthetic doses (a fraction of what’s used in surgery) given on a controlled schedule, while recreational users may take far larger amounts multiple times a day. The clinical doses studied so far don’t appear to cause the same kind of cognitive damage, but long-term data spanning years of maintenance treatment is still limited.
Bladder and Urinary Risks
Ketamine-related bladder damage is well documented in recreational users. An estimated 26 to 30 percent of regular recreational users experience at least one bladder symptom, including frequent urination, urgency, pain, and in severe cases, a dramatically shrunken bladder that requires surgical intervention. The damage appears to come from ketamine’s byproducts irritating and breaking down the bladder’s protective lining, triggering chronic inflammation.
Using ketamine at least three times a week for two years or more has been linked to significant bladder problems. Recreational users commonly take 50 to 200 milligrams four to five times daily, which is dramatically more than the typical clinical dose of 0.5 milligrams per kilogram given once or twice a week. The severity of bladder symptoms is directly tied to dose and frequency. At clinical doses and schedules, bladder damage has not been a reported concern in the research, but anyone on long-term maintenance treatment should be aware of this risk and report urinary symptoms early.
Addiction Potential
Ketamine does have addictive properties. Lab studies show it produces brain changes typical of drugs with abuse potential, and research in humans confirms that regular users can develop tolerance, use more than intended, and continue using despite negative consequences. The National Institute on Drug Abuse notes that unsupervised ketamine use carries serious health risks.
In a clinical setting, several safeguards reduce this risk. The FDA-approved nasal spray form (esketamine, sold as Spravato) can only be administered in certified healthcare settings under direct observation. Patients cannot take doses home. You self-administer the spray while a healthcare provider watches, then you’re monitored for at least two hours before leaving. Pharmacies can only dispense it to certified clinics, not directly to patients. For IV ketamine, which is used off-label, similar in-clinic protocols are standard, though the specific safeguards vary by provider.
That said, the controlled setting doesn’t eliminate the risk entirely. Some patients may seek ketamine from other sources between appointments, and the pleasant or dissociative effects can be psychologically reinforcing. If you have a history of substance use disorder, this is worth discussing openly with your provider before starting treatment.
Safety Considerations for Older Adults
Older adults face a distinct set of risks. The liver processes ketamine more slowly with age, leading to higher drug levels in the blood and a greater chance of side effects at standard doses. The brain also becomes more sensitive to anesthetics over time, meaning a smaller dose produces a stronger effect. Hallucinations, confusion, and delirium are more common in elderly patients, especially at higher doses, and these effects can be particularly disruptive for someone with existing cognitive vulnerabilities.
For these reasons, providers typically use lower doses for older patients, generally in the range of 0.15 to 0.5 milligrams per kilogram delivered intravenously. Slow continuous infusions are preferred over rapid single doses to minimize the risk of psychotic-like side effects. At these adjusted doses, research suggests a reasonable balance between therapeutic benefit and safety, though close monitoring remains essential.
How Effective It Actually Is
Safety exists in the context of benefit, and ketamine’s effectiveness matters when weighing its risks. A real-world study from the VA health system found that after six weeks of treatment, 26 percent of patients experienced a meaningful response (at least a 50 percent reduction in depression symptoms) and 15 percent achieved remission. Those numbers are modest but significant for a population with treatment-resistant depression, meaning they’ve already tried and failed other medications. For many of these patients, ketamine represents one of the few remaining options, which shifts the risk-benefit calculation considerably.
The rapid onset of effect is another factor. Traditional antidepressants take four to six weeks to work, while ketamine can produce noticeable improvements within hours to days. For someone experiencing severe depression with suicidal thoughts, that speed has real clinical value, which is why one of esketamine’s FDA-approved uses is specifically for adults with major depression and acute suicidal ideation.