Ketamine therapy carries real risks, but serious medical complications are rare when it’s administered at clinical doses with proper screening. In a systematic review of over 3,750 patients who received sub-anesthetic ketamine for psychiatric conditions, only four experienced a serious medical adverse event, an incidence of roughly 0.1%. No cardiac emergencies or deaths were observed. That said, common side effects are frequent, certain medical conditions make ketamine unsafe, and the long-term picture still has gaps worth understanding.
Common Side Effects During Treatment
Most people who receive ketamine will feel something during and shortly after a session. The most frequent side effect is dissociation, a feeling of being detached from your body or surroundings, which occurs in about 62% of patients. Dizziness or faintness affects around 37%, and nausea shows up in about 16%. These effects are temporary, typically resolving within one to two hours after the dose.
Because of these short-term effects, the FDA-approved nasal spray form of ketamine (esketamine) requires patients to be monitored for at least two hours after each session. You can’t drive until the following day after a restful sleep. Blood pressure gets checked before the session and again around 40 minutes after dosing, which is when it tends to peak. If your blood pressure hasn’t stabilized by the two-hour mark, monitoring continues until it does.
Blood Pressure and Heart Effects
Ketamine stimulates the sympathetic nervous system, your body’s “fight or flight” response, which temporarily raises blood pressure, heart rate, and cardiac output. In one study of adults receiving ketamine for procedural sedation, 29% experienced a blood pressure or heart rate spike of 20% or more immediately after the dose. At some point during the procedure, 71% of patients hit that threshold.
For most healthy people, these increases are mild and short-lived. But they’re the main reason people with uncontrolled high blood pressure or a history of heart problems are typically screened out before treatment begins. The FDA lists increased blood pressure as a known safety concern, and clinics routinely take baseline readings and monitor throughout the session.
Bladder Damage With Repeated Use
One of the more serious long-term risks tied to ketamine is bladder inflammation, sometimes called ketamine-induced cystitis. This was first documented in 2007 among people using ketamine daily, and the damage is clearly dose-dependent: the more frequently you use it and the higher the dose, the greater the risk.
Among recreational users, over 25% report urinary symptoms. About 20% of frequent users develop cystitis-like problems compared to roughly 7% of infrequent users. In severe cases, nearly 90% of patients showed thickened bladder walls on imaging, and 44% had signs of kidney backup. These numbers come from recreational use, which involves far higher doses and more frequent exposure than clinical therapy. Still, it’s a meaningful concern for anyone on long-term or repeated treatment, and something to discuss with your provider if you notice changes in urinary frequency or discomfort.
Addiction Potential in Clinical Settings
Ketamine is a controlled substance with known potential for misuse, which understandably makes people nervous about receiving it as a treatment. In practice, though, the data from clinical and research settings is reassuring. One research group reported treating over 1,000 patients without a single case of ketamine use disorder developing. Across multiple clinical trials for depression and substance use disorders, no participants initiated drug misuse as a result of ketamine treatment.
In one study focused on alcohol use disorder, six participants did use ketamine illicitly on a single occasion after their infusions, but all six had already been recreational ketamine users before the trial. No new patterns of misuse emerged in people without that history. The broader pattern across all reviewed studies: no major long-term psychiatric effects and no development of substance use disorders from ketamine delivered in a research or clinical context.
Effects on Memory and Thinking
Short-term, low-dose ketamine doesn’t appear to impair cognition. In fact, a systematic review found that acute administration at low doses not only preserved memory but actually improved visual memory and working memory in people with treatment-resistant depression.
Chronic use is a different story. Functional brain imaging of long-term recreational ketamine users revealed decreased activity in brain regions responsible for spatial memory. These users experienced measurable memory disturbances, and some developed psychotic symptoms. The concern for clinical patients is that repeated treatments over months or years could eventually produce similar effects, though the doses involved in therapy are substantially lower than recreational use. Some researchers have noted that sublingual (under the tongue) ketamine, which has lower absorption into the bloodstream, may help reduce cognitive side effects compared to intravenous delivery.
Drug Interactions That Matter
If you’re already taking psychiatric medications, some can interfere with how well ketamine works. Benzodiazepines, commonly prescribed for anxiety, have been repeatedly shown to reduce the duration of ketamine’s antidepressant effect. At higher doses (equivalent to 10 mg or more of diazepam), benzodiazepines predicted non-response to ketamine treatment during the first week of follow-up. Lamotrigine, a mood stabilizer, may also blunt ketamine’s effects based on some studies.
These interactions don’t necessarily make the combination physically dangerous, but they can make treatment less effective. If you take benzodiazepines or lamotrigine, your provider should factor that into the treatment plan.
Clinic-Based vs. At-Home Ketamine
One of the biggest variables in how risky ketamine therapy is comes down to where and how you receive it. In a clinic, you’re screened for cardiovascular risk, monitored for two hours, and observed by a healthcare provider throughout. At-home programs, which have expanded through telehealth platforms, use sublingual or oral formulations at lower doses with remote monitoring instead of in-person supervision.
A large open-label trial of at-home sublingual ketamine found that adverse event rates were consistent with what’s seen in clinic settings. Four patients left treatment due to side effects, and two more due to adverse events. Patient screening and remote monitoring kept complication rates low. However, the FDA has specifically warned about compounded ketamine products sold through telehealth, flagging risks of abuse, respiratory depression, psychiatric events, and blood pressure spikes when these products are used outside the controlled environment of a certified healthcare setting.
Who Should Avoid Ketamine Therapy
Certain conditions make ketamine therapy genuinely unsafe. The FDA’s listed safety concerns point to several high-risk groups:
- Uncontrolled high blood pressure: ketamine’s cardiovascular stimulation can push already elevated blood pressure into dangerous territory
- Active psychosis or unstable psychiatric disorders: ketamine can trigger or worsen psychiatric symptoms
- History of ketamine misuse: existing vulnerability to substance use disorder raises the risk profile
- Respiratory conditions: ketamine can slow breathing, which is more dangerous in people with compromised lung function
- Bladder or urinary tract problems: existing urological issues can be aggravated by ketamine exposure
Most clinical trials have excluded patients with high cardiovascular risk, which means the reassuring safety statistics come from a pre-screened population. If you have heart disease or uncontrolled blood pressure that wasn’t caught in screening, your actual risk would be higher than what the studies reflect.