Ketamine side effects: definition, risks and what patients should know before surgery

Definition: Ketamine side effects are undesirable physical and psychological reactions to the active ingredient ketamine, a dissociative anaesthetic and painkiller that blocks the NMDA receptor. The side effects range from temporary changes in perception to permanent organ and brain damage, depending on the dose, frequency of use and the level of medical supervision.

Ketamine is an active substance with an unusually broad range of applications: Paramedics use it as a fast-acting painkiller, anaesthetists employ it in certain surgical situations, and since the approval of esketamine nasal spray (Spravato), it has also been used to treat treatment-resistant depression. Anyone planning cosmetic surgery will come into contact with ketamine themselves, so it is worth taking a closer look at this active ingredient’s side-effect profile.

Ketamine side effects explained: background and details

Ketamine was developed in the USA in 1962 and replaced the more dangerous phencyclidine (PCP) as an anaesthetic. The substance belongs to the class of dissociative anaesthetics. The term „dissociative“ describes its characteristic effect: ketamine separates sensory perception from conscious processing in the brain. Patients remain outwardly responsive, but at the same time experience a profound alteration of consciousness.

It is precisely this effect that makes ketamine both medically valuable and prone to abuse. As Anaesthetics It maintains vital protective reflexes such as breathing and circulation, which is an advantage over other anaesthetics. As a party drug (street names: Special K, Vitamin K, Kate), however, it is specifically consumed to alter consciousness, without any medical supervision.

For the 4beauty glossary, the following question is particularly relevant: Which side effects of ketamine are of significance to people planning to undergo cosmetic surgery? The answer depends on the context in which ketamine is used and the dose administered. The following sections explain this distinction.

According to the Federal Centre for Drug Education (BZgA), drugcom.de, ketamine is now rarely used as a primary anaesthetic, but remains an indispensable painkiller in emergency medicine and during certain surgical procedures where other anaesthetics are contraindicated.

How ketamine causes side effects in the body: mechanism of action

Ketamine acts as a NMDA receptor antagonist (NMDA stands for N-methyl-D-aspartate) is an important ion channel in the brain. This channel is involved in the transmission of pain signals and in memory formation. The block occurs in several stages:

1. Absorption into the bloodstream: Ketamine is administered intravenously, intramuscularly or intranasally. It crosses the blood-brain barrier very quickly.
2. NMDA blockade: In the brain, ketamine blocks the NMDA receptor allosterically; this means that it does not bind directly to the site of action, but alters the receptor’s structure in such a way that glutamate (the most important excitatory neurotransmitter) can no longer bind to it.
3. Dissociative effects: The disruption of glutamate neurotransmission leads to the characteristic dissociation: pain stimuli no longer reach consciousness, and perception becomes disconnected from bodily sensation.
4. Antidepressant mechanism: By inhibiting the mTOR signalling pathway and triggering the release of BDNF (brain-derived neurotrophic factor), ketamine – particularly in the form of esketamine – is effective in treating treatment-resistant depression, with the effect becoming apparent within just a few days.
5. Dismantling: The half-life of ketamine is approximately 10–15 minutes during the initial phase; complete metabolisation in the liver takes longer. Metabolites are excreted in the urine.

Acute side effects of ketamine: a comprehensive overview

Psychological side effects: hallucinations, K-hole and altered states of consciousness

The psychological side effects of ketamine stem directly from its dissociative mechanism of action. Visual and auditory hallucinations can occur even at low doses. At higher doses, particularly with uncontrolled use, there is a risk of the so-called K-Hole: a state of profound loss of self-awareness, similar to near-death experiences. Those affected report out-of-body experiences, the sensation of floating or observing themselves from the outside.

Overview of acute ketamine side effects by category. In a clinical setting, cardiovascular effects are monitored continuously. As at July 2026.

Some users deliberately seek out the ‘K-hole’, but it is often accompanied by intense panic and poses a significant risk of accidents. In a medical setting, psychological reactions following anaesthesia are alleviated by benzodiazepines (sedatives).

Physical side effects: blood pressure, heart rate and respiratory system

Ketamine stimulates the sympathetic nervous system, thereby increasing blood pressure and heart rate – an effect that is deliberately utilised in emergency medicine for patients with circulatory instability. However, in people with pre-existing heart conditions, this increase can pose a risk. Nausea and vomiting frequently occur during the recovery phase following ketamine anaesthesia; dizziness and confusion usually subside within a few hours in healthy adults.

Long-term effects and organ damage associated with chronic ketamine use

Ketamine bladder: Damage to the bladder caused by regular use

The Ketamine-induced cystitis, commonly known as ‘ketamine bladder’, is one of the most serious long-term consequences of regular ketamine use. Ketamine and its metabolites are excreted via the kidneys and, in the process, come into direct contact with the bladder lining. With regular use over a period of months, chronic inflammation develops, leading to fibrosis (scarring) of the bladder. Those affected suffer from a strong urge to urinate, painful urination and, in advanced stages, a drastically reduced bladder capacity. In severe cases, surgical bladder reconstruction is necessary.

Brain damage and its effects on memory

Regular ketamine use has been shown to damage the Short-term memory and episodic memory (the ability to place personal experiences in a chronological context). In the long term, the central nervous system (CNS) may be permanently impaired. Recent neurobiological research shows that chronic use permanently alters synaptic plasticity – the adaptability of nerve cells. This can lead to memory lapses, problems with concentration and depression.

Addiction and withdrawal symptoms

Ketamine has the potential to cause psychological dependence. Withdrawal symptoms following regular use – an aspect that is rarely discussed in public debate – include anxiety, irritability, sweating and insomnia. Physical withdrawal symptoms are less pronounced than with opiates, but may occur in cases of severe dependence and should be managed under medical supervision.

Ketamine in cosmetic procedures: what patients should know

Ketamine is used as part of the anaesthesia for certain cosmetic procedures, such as liposuction or procedures where deep sedation is required without full respiratory support. The key difference compared to recreational use lies in the controlled environment.

In the operating theatre, the dosage and administration are precisely controlled by anaesthetists. Vital signs such as blood pressure, heart rate and oxygen saturation are continuously monitored. Psychological side effects such as hallucinations are significantly reduced by the use of accompanying medication (usually benzodiazepines). Under these conditions, the risk of a ‘K-hole’ is negligible.

Nevertheless, even when carried out correctly, unforeseen complications can arise: allergic reactions, unexpected rises in blood pressure or post-operative confusion. Anyone planning cosmetic surgery should be aware of these risks and know that Insurance against consequential costs are designed specifically for situations like these. Further information on the treatments covered can be found in the Overview of treatments at 4beauty.

Ketamine is not suitable for self-medication, nor is it a harmless recreational drug. However, for patients with no pre-existing conditions who undergo surgery at a certified clinic, ketamine is a well-established anaesthetic that is easy to manage when used correctly.

Common misconceptions about the side effects of ketamine

There are two common misconceptions that patients frequently encounter before undergoing cosmetic procedures:

Misconception	Fact-based assessment
Ketamine is completely harmless when used under medical supervision.	Side effects such as an increase in blood pressure, nausea and post-operative confusion may also occur in a clinical setting. Medical supervision reduces, but does not eliminate, every risk.
Ketamine, when used as a party drug, poses only psychological risks.	Chronic abuse causes physical damage to the bladder and the brain, some of which is irreversible.
After a single dose of ketamine anaesthesia, you are immediately fit to drive again.	Following anaesthesia with ketamine, the ability to drive is impaired for at least 24 hours. Patients should not operate machinery or make any important decisions.
Ketamine is not addictive.	Ketamine has a proven potential for psychological dependence; withdrawal symptoms may occur with regular use.

Frequently Asked Questions about the Side Effects of Ketamine

Sources and further links

• drugcom.de / BZgA
• Yellow List
• AOK Magazine