Ketamine’s most common side effects are dissociation, dizziness, nausea, and a temporary spike in blood pressure. These effects are well-documented in clinical settings, where nearly half of patients experience some degree of dissociation during treatment. The specific side effects you might encounter depend heavily on whether ketamine is used once in a medical setting or repeatedly over weeks and months.
The Most Common Side Effects During Treatment
Clinical trial data from the FDA review of esketamine (a nasal spray form used for depression) gives the clearest picture of how often side effects occur. In adults under 65, about 47% experienced dissociation, meaning a feeling of being detached from your body or surroundings. Roughly a third reported dizziness, a quarter felt sedated, and about 28 to 32% had nausea. Vertigo, a spinning sensation distinct from general dizziness, affected around 21% of patients.
These effects tend to peak during or shortly after administration and fade within a couple of hours. In clinical settings, patients are monitored for at least two hours after treatment before being cleared to leave. An advanced life support-certified provider stays with the patient until discharge, and staff assess both vital signs and mental clarity before sending anyone home.
Older adults (65 and up) generally experience the same side effects at somewhat lower rates: about 21% report dissociation, 24% dizziness, and 18% nausea. Lethargy is more notable in this group, affecting around 14%.
Blood Pressure and Heart Rate Changes
Ketamine stimulates the cardiovascular system. It raises heart rate, blood pressure, and cardiac output, which is actually one reason it’s sometimes preferred for sedation in emergency medicine (it doesn’t cause the dangerous blood pressure drops that other sedatives can). But for people with heart conditions or high blood pressure, this stimulation is a real concern.
Studies show that 10 to 50% of patients experience a measurable rise in blood pressure during infusion. On average, systolic blood pressure (the top number) rises by about 16 points and diastolic (the bottom number) by about 11 points, peaking around 40 minutes after the infusion starts. In a study of 84 patients across 205 infusions, 20 to 30% had blood pressure exceed 180/100 or a heart rate above 110 beats per minute, and 12 of those patients needed medication to bring their blood pressure down. Severe spikes were more common during the first three infusions than later ones.
This is why most clinical trials and treatment programs screen out people with uncontrolled hypertension, aneurysms, or other cardiovascular risks. In a systematic review of ketamine trials for psychiatric conditions, 83% of studies reported excluding high-risk cardiac patients, and no serious cardiac events or deaths were observed among the remaining participants.
Bladder and Urinary Tract Damage
One of ketamine’s most distinctive long-term risks is bladder damage, sometimes called ketamine-induced cystitis. This primarily affects people who use ketamine frequently over months or years, particularly recreational users. Symptoms include severe pelvic pain, blood in the urine, an urgent and frequent need to urinate (sometimes dozens of times a day), and a dramatically reduced bladder capacity.
The condition involves inflammation and thickening of the bladder wall. In severe cases, the bladder can shrink to a fraction of its normal size and require surgical reconstruction. The exact mechanism isn’t fully understood, but ketamine and its breakdown products are excreted through urine and appear to directly irritate and damage the bladder lining. Case reports describe patients with as little as seven months of daily use developing symptoms serious enough to require emergency care. Early cases can improve if ketamine use stops, but advanced damage is often irreversible.
Cognitive Effects With Repeated Use
Chronic ketamine use impairs memory and executive function, which is your brain’s ability to plan, focus, and juggle multiple tasks. A study comparing 165 chronic ketamine users to 111 drug-free controls found significant deficits in verbal memory, visual memory, and executive function among the ketamine group. Brain imaging studies of long-term users have also shown reduced gray matter volume in the frontal regions of the brain.
The mechanism is straightforward: ketamine blocks a receptor that plays a central role in synaptic plasticity, the process your brain uses to strengthen connections between neurons during learning and memory formation. Blocking this receptor temporarily produces the dissociative and antidepressant effects that make ketamine useful in medicine, but doing so repeatedly over time appears to impair the brain’s ability to form and retrieve memories effectively. How much of this damage reverses after stopping use is still an open question, though some recovery has been observed in people who achieve sustained abstinence.
Liver and Bile Duct Problems
Heavy or prolonged ketamine use can damage the bile ducts, a condition called ketamine-induced cholangiopathy. This shows up as abnormal liver enzyme levels, dilation of the bile ducts, and the formation of strictures (narrowed sections) in the biliary system. Several mechanisms likely contribute: ketamine may trigger inflammation and scarring in the bile duct lining, directly damage the cells that line the ducts, and increase resistance to bile flow.
This is primarily a concern for chronic, heavy users rather than patients receiving occasional medical infusions. But elevated liver enzymes have been documented in case reports even at moderate durations of use, making it something clinicians watch for in patients on longer treatment courses.
Psychological Side Effects
Beyond the dissociation that most users experience acutely, ketamine can trigger anxiety, agitation, and vivid or disturbing perceptual changes during and shortly after use. Some people find the dissociative state pleasant or neutral, while others find it deeply unsettling. In medical settings, patients are warned ahead of time that they may feel detached from reality, experience unusual sensory perceptions, or feel a sense of unreality that typically resolves within two hours.
People with a history of psychosis are generally excluded from ketamine treatment programs because the drug can temporarily produce psychosis-like symptoms: paranoia, hallucinations, and disordered thinking. These effects are dose-dependent and far more likely at higher (anesthetic) doses or with recreational use than at the lower doses used for depression treatment. That said, even sub-anesthetic doses can be psychologically intense, which is part of why supervised administration with post-treatment monitoring is standard practice.
Tolerance, Dependence, and Withdrawal
Ketamine produces tolerance quickly, meaning regular users need increasing amounts to achieve the same effect. This escalation drives many of the long-term complications, particularly bladder damage and cognitive impairment, because the total amount of ketamine passing through the body increases over time. Physical dependence can develop with regular use, and withdrawal symptoms include cravings, anxiety, sweating, tremors, and disturbed sleep. Psychological dependence, where users feel unable to cope or function without the drug, is also well-documented among chronic recreational users.
In medical settings, the risk of dependence is managed by using low doses on a limited schedule, typically twice a week during an initial phase and then tapering to once a week or less. The supervised nature of clinical administration also removes the self-dosing pattern that drives recreational dependence.