What Are the Potential Side Effects and Risks of Ketamine Use?

Clinically reviewed by Dr. Aviva Wolf — Consultant Psychiatrist · Last reviewed 9 July 2026

Ketamine has real value in medicine, but that reputation for safety can be misleading. Its side effects fall into two very different groups: the acute effects felt within minutes of a dose, and the slower, more serious harms that build up with chronic or heavy use. Understanding both is what tells you when ketamine has stopped being manageable — and this guide from Holina Rehab in Koh Phangan, Thailand walks through the full profile.

If you are researching ketamine’s legitimate medical role, our companion article covers the therapeutic uses of ketamine. Here the focus is different: what ketamine actually does to the mind and body, dose by dose and year by year.

Short-term side effects of ketamine

Ketamine acts fast. Effects usually appear within minutes and vary with the dose, the route (snorted, swallowed or injected) and individual factors such as body weight and metabolism. The most common acute effects are:

• Dissociation and derealisation: a hallmark feeling of being detached from your body and surroundings, often with visual or auditory distortions and a warped sense of reality (Alcohol and Drug Foundation).
• Raised blood pressure and heart rate: ketamine stimulates the sympathetic nervous system, and blood pressure and heart rate typically climb within the first hour of a dose. This is well tolerated by most healthy people but can be hazardous with an existing heart condition (Frontiers in Psychiatry, 2022).
• Nausea and vomiting: common, and a genuine risk when someone is heavily dissociated and less able to protect their airway.
• Dizziness, drowsiness and poor coordination: reaction times and balance are impaired, which is why accidents and falls are frequent.
• Confusion and disorientation: difficulty concentrating and disordered thinking, more pronounced at higher doses.

These effects are usually transient, easing within a few hours, but they can be distressing and dangerous — especially outside a controlled setting where no one is monitoring the person.

What a “k-hole” actually is

At higher doses the dissociation can tip into what users call a “k-hole”: a state of extreme detachment where a person becomes almost completely disconnected from their body and environment, sometimes unable to move or speak (Alcohol and Drug Foundation). Some people find it frightening; others chase it — and that pursuit of a deeper dissociative escape is often where recreational use starts to slide toward a problem.

Long-term risks of heavy ketamine use

Repeated, heavy use is where ketamine’s reputation as “low-risk” falls apart. Several harms accumulate quietly over months and years:

• Memory and cognitive impairment: frequent users show measurable deficits in short- and long-term memory, attention and learning. Encouragingly, some of these impairments appear to ease in people who have been abstinent for a year or more, suggesting the damage is at least partly reversible when use stops (Morgan & Curran, 2012, Addiction).
• Liver and bile-duct injury: a less-known but serious ketamine-specific risk. Chronic use is linked to cholestatic liver injury and ketamine-induced cholangiopathy — bile-duct damage that can resemble primary sclerosing cholangitis, with abdominal pain, jaundice and abnormal liver enzymes. A systematic review found liver injury in close to one in ten chronic users (Hepatobiliary Complications of Ketamine Use, systematic review, 2024).
• Bladder and urinary damage: heavy use can cause ketamine-induced cystitis, a painful and potentially irreversible bladder condition. We cover this in depth — and why it becomes a vicious cycle — in our guide to the four questions we hear most about ketamine.
• Psychological dependence: tolerance builds quickly, so doses creep up, and regular users often find it genuinely hard to stop — cravings, low mood and compulsive use are the recognised hallmarks of ketamine dependence (Alcohol and Drug Foundation).
• Mood disturbance: chronic use is associated with persistent low mood, anxiety and worsening of any underlying mental-health condition.

Why recreational use is more dangerous

Outside a clinic, the same drug carries extra hazards that have nothing to do with the pharmacology and everything to do with the setting:

• Overdose and airway risk: illicit ketamine varies wildly in strength, and heavy dissociation raises the risk of choking on vomit or losing consciousness. Fatal overdose on ketamine alone is uncommon, but combining it with alcohol, opioids or benzodiazepines — all central-nervous-system depressants — is where the real danger lies.
• Impaired judgement: dissociation and poor coordination make accidents, injuries and risky decisions far more likely.
• Contaminated supply: illegally sourced ketamine may be cut with unknown substances, producing unpredictable and dangerous reactions.

How clinical use manages these risks

In medicine, ketamine is given for anaesthesia and, increasingly, for treatment-resistant depression and some pain conditions — but always under strict supervision. Precise, individually calculated dosing, continuous monitoring of vital signs and immediate access to medical support mean adverse reactions are caught early. Patients are screened for contraindications such as uncontrolled high blood pressure, a history of psychosis or a substance-use disorder. It is exactly this framework of oversight that recreational use removes, which is why the same molecule behaves so differently in the two settings.

A word from our clinical team

“People tend to fixate on the k-hole and the immediate high, but it is the slow-burn harms that bring most people to us — the memory that is not what it was, the bladder pain, and increasingly the liver. Ketamine-related liver injury is still under-recognised, and I’d urge any regular user with unexplained abdominal pain or jaundice to get their liver function checked. The reassuring part is that the brain, bladder and liver often recover meaningfully once use stops and the reasons behind it are treated.”

— Dr. Aviva Wolf, Consultant Psychiatrist, Holina Rehab

Draft quote — pending Dr. Aviva Wolf’s final sign-off.