Ketamine Side Effects: Physical, Mental and Long-term Effects

Published On: November 15, 2023

Ketamine is categorised as a dissociative anaesthetic drug which is primarily used as a sedative medication and as an anaesthetic on patients prior to them having an operation or medical procedure. (4,5)

The range of medical conditions that ketamine can assist in treating has grown steadily over recent years thanks to the abundance of research that has been carried out on the drug.

Ketamine has been recognised as having therapeutic properties that can:

  • Help with anaesthesia.
  • Help with pain relief.
  • Alleviate anxiety.
  • Treat depression (including post-natal depression and treatment-resistant depression).
  • Acting as a bronchodilator, ketamine helps to soothe airways to aid the breathing process. (4,5)

Characteristics of ketamine

Mixing Pills

Ketamine is capable of slightly stimulating the heart but does not negatively impact the respiratory process (unless it is taken at high doses) or stop the gag reflex. T

his means it has a good safety record and is therefore a reliable intervention for many medical conditions.

Ketamine is known to take effect quickly which is why it has gained such notoriety as a recreational drug as its effects can be experienced in minutes.

Ketamine is a powerful and complex drug.

Two people holding hands across a table

The fact that ketamine has so many medical uses indicates what a powerful and complex drug it is, and this is reflected in the fact that it can behave differently depending on how much has been taken.

For example, at lower levels (which can still be harmful) users can experience its euphoric effects and feel mildly sedated and calm accompanied by a sense of floating.

However, when taken at higher doses it will eventually have a depressive effect on the brain, which can bring on intense, frightening hallucinations and altered perceptions as users are on their way to consuming a dose that could render them unconscious. (2,8)

There are small margins between safe and harmful doses

Worryingly, there is a small margin between a safe dose and a dose that could cause an overdose which could be fatal for people taking ketamine for the first time, or users who mix ketamine with other drugs for the first time.

Ketamine affects many systems and processes in the brain and not all of these effects are fully comprehended by scientific researchers who have investigated the effects of the drug. (2,8)

Positive side effects sought after by recreational users.

A group of people saying cheers with various drinks

Due to the complex nature of drug design and the human body, all drugs have more than one effect on human biology and chemistry, meaning they can affect us in several ways.

The chemical structure of ketamine means that even though it has several uses in medicine there are people who are keen to experience the positive effects generated by the drug.

For ketamine, this includes:

  • Pleasure
  • Relaxation / mild sedation.
  • Hallucinations, both auditory and visual.
  • A sense of detachment.
  • Floating and out-of-body experiences. (2,8)

What is a side effect?

Woman looking sad

A side effect is an unwanted and adverse reaction that a person experiences when taking a medicine to help treat a condition or physical problem or to alleviate a range of unpleasant symptoms.

All drugs that treat physical and psychiatric conditions contain many different chemical elements, each of which has a different strength. (3)

Why do drugs produce side effects?

A woman taking a white pill

All drugs used for medical purposes will produce other effects on top of the purpose they are being prescribed for. This is because both the human body and the act of designing and adapting drugs are very complex to understand.

There is a range of chemicals in all medical and psychoactive drugs and it is unlikely that any drug will just target one area of human biology alone and not affect any other physical processes in the human body.

All medications, therefore, are highly likely to come with side effects for most users but in most cases, they are easily managed and do not tend to cause too much disruption to our day-to-day life only really causing us minor inconveniences.

The more powerful and complex the drug is the more problematic and uncomfortable the side effects are likely to be. (1,9)

Side effects can occur during or just after taking ketamine (for medical treatment)


Ketamine will invariably cause side effects, but these effects are more likely to occur when ketamine is taken at higher doses. As ketamine is a complex drug it is very difficult to accurately predict these effects consistently as even the same person can experience different effects at different times.

The side effects likely to be experienced just after taking ketamine for medical reasons include:


A person experiencing this effect may report that their body and mind feel like they are separate from one another and they may use the term “out of body” to describe what they are experiencing.

They may feel like their arms or hands “don’t belong” to them. People experiencing this state often describe a floating sensation. (1,5)

Ego dissolution

This may be described as feeling an interconnectedness or oneness with everything around them, including other people and their environment. This can seem like a spiritual, enlightening experience which some people have reported as “awesome” but others have found frightening. (7,9)

Changes in perception

There may also be a change in a person’s perception of the people, places and surroundings that they come into contact with. They may perceive their behaviour differently and interpret seemingly innocent remarks made by others as threats or insults.

Their perception may reflect their current mood and mental state at the time. People experiencing a change in perception may feel that the sights and sounds they are perceiving are different to normal or that their friends are acting “weird”.

This may be accompanied by:

  • Dizziness and/or light-headedness, similar to the experience of drinking too much alcohol.
  • Fatigued and low on energy.
  • Headaches


It is common to feel nauseous after taking ketamine and there are medications available to help counteract these nauseous feelings. It is therefore not advisable to eat a meal 2-3 hours before taking ketamine (as a patient). (1,9)


Many patients develop anxiety to varying degrees, at its most extreme people who take ketamine can feel a sense of panic which can appear suddenly at any moment from nowhere and catch them by surprise.

Fortunately, most people who experience anxiety will find that the symptoms will pass very quickly, usually in 10-15 minutes as the ketamine begins to be processed by the body.

It is important to be aware of this effect so patients can understand what is happening and not overly panic as the effects are usually short-lived. (1,5)


Some people may experience a loud “ringing in their ears” which can get even louder for those people who already have problems with tinnitus, but the condition can also develop in people who have not experienced such problems before.

Taking other drugs that are known to cause tinnitus such as venlafaxine and duloxetine is likely to increase the likelihood of developing tinnitus if you take ketamine.

Medical specialists investigating the area have concluded that tinnitus does disappear when people stop taking ketamine but there is also the slight possibility that a person’s hearing may be continued to be affected for some time afterwards. If tinnitus still occurs after ketamine use has stopped then it is important to inform your GP who will investigate further.


Some individuals may experience temporary bruising in the area where the needle was placed into the vein during ketamine infusion treatment. The needle is usually placed into the vein in the back of a patient’s hand. (5,9)

Less common side effects

  • Vivid dreams.
  • Hallucinations
  • Mania (Elevated mood and energy)

Rare side effects (physical)

Possible long-term risks

Long-term effects of ketamine use

Man with his head in his hand, eyes closed, in a gesture of pain

If people are taking ketamine for medical purposes then ideally they should not be taking the drug for too long as they may experience many unpleasant side effects if they take the drug for longer than they need to

The main, common side effects that people who regularly take ketamine are likely to experience include:

  • Nausea and vomiting.
  • Dizziness/ light-headedness.
  • Dysphoria (a dissatisfied, unhappy state).
  • Double vision.
  • Drowsiness
  • Delirium (Confusion)

There are other many other potential side effects apparent that patients can experience that fall into the following categories:

  • Allergic reactions.
  • Cardiovascular complications.
  • Gastrointestinal
  • Muscular/ skeletal.
  • Neurological
  • Ophthalmologic
  • Breathing / respiratory system.
  • Skin
  • Psychiatric (8)

Side effects guidance for ketamine

It is important to state that the medical advice regarding side effects is based on carefully measured and controlled doses that clearly indicate the strength and precise chemical composition of the ketamine doses they will be taking.

People who take ketamine recreationally will be unable to quantify exactly how much ketamine they have taken. This is due to the inaccuracy in establishing precise dose strengths and the specific chemical content contained in the ketamine that is available on the illicit market.

This in itself can lead to people underestimating the strength of the side effects that they may experience.

Side effects for recreational users


Because of the higher amounts of ketamine taken by recreational compared to medical patients, they are more vulnerable to developing a wide range of effects that could become permanent if their ketamine use is sustained for a significant period of time. (1,5,9)

The side effects that recreational users may experience will probably be more severe and erratic if they have regularly ingested the drug over a period of months. It is also likely that there may be other new side effects that may appear.

This is because the chemical makeup of illicitly obtained ketamine is likely to be drastically different to medical doses making it harder to precisely predict the side effects.

The side effects that have been reported with prolonged ketamine use include:

  • AllergiesLaboured breathing, the possibility of anaphylaxis, swelling to tongue, lips and hives may appear.
  • HeartIncrease in blood pressure, arrhythmia, hypotension (low blood pressure) slowing down of the heart, potentially leading to cardiac arrest.
  • Digestive/gastrointestinalNausea, heavy vomiting, the possibility of developing anorexia nervosa.
  • BrainThreat of seizures. May experience delirium.
  • Muscular/skeletal effects – Muscle spasms and stiffness throughout the body,
  • Respiratory Respiratory depression, development of sleep apnoea. laryngospasm
  • SkinInfection and/or pain at the site of injection, rashes, erythema
  • BladderSevere bladder problems.
  • Psychiatric effectsAnxiety, symptoms of depression, disassociation and disorientation.
  • Insomnia, hallucinations, flashbacks.
  • Behaviour Irrational, fearful (1,8)

Interaction effects

Men talking

It is important to recognise that the side effects associated with ketamine use whether medically or recreationally can be made worse, or altered when ketamine is combined with other medications, recreational drugs and especially alcohol.

Ketamine is a drug which is currently not fully understood by medical researchers so its individual effects are not yet clearly established let alone the effects that are generated when combined with other psychoactive substances.

Although it is easier for doctors to detect any interaction effects that occur when ketamine is combined with carefully measured doses of approved medicines.

However, the side effects that occur when ketamine is combined with recreational drugs whose chemical contents and potency levels are unknown can lead to several unpredictable and life-threatening conditions affecting:

  • Cardiac functioning.
  • Overdose risk.
  • Breathing
  • Psychiatric health (increased risk of suicide).
  • Brain processes (including the risk of seizures).
  • Sleep patterns. (1,7,9)

Ketamine as a treatment for depression

Support Group

Over recent years ketamine has drawn a lot of attention in the medical and psychiatric community for its successful use on patients diagnosed with “difficult to treat” depression.

However, there is still a lot of uncertainty about the physiological reasons which lead to these promising results and there is still a long way to go before ketamine becomes approved as a licensed drug for depression on the NHS. (1,7,8)

However, even though single medical doses of ketamine that are lower than the amount needed to anaesthetise a patient have helped lower depressive symptoms, scientists analysing the drug have been concerned about some of the side effects that patients experienced.


Individual therapy

There have been concerns raised about the increase in the “off-label” (not medically approved) use of ketamine via the intravenous route and the fact that this could lead to several unpredictable and harmful side effects.

The concern is mainly focused on the fact that ketamine is a highly sought-after drug for recreational users and is considered a high risk for physical dependence. (1,7)

When assessing the side effects of ketamine treatment for depression the main side effect reported by patients was feeling strange or loopy. Most of the side effects reached their peak an hour after the drug was ingested and disappeared two hours after being taken.

Medical trials have revealed that there was no evidence of the treatment causing any harmful, or adverse effects,  although no research studies have examined the long-term effects of regular ketamine infusion as a treatment for depression.

Side effects of ketamine infusion

Data collected from over 150 patients examined 120 possible side effects that may be expected to appear.

Overall, 34 effects were found to be significantly associated with the treatment, with over 50% of the people taking part experiencing 8 side effects, none of which appeared for more than 4 hours or were present 3 months later.

These 8 effects included:

  • Reports of feeling strange or weird.
  • Feeling “spaced out”.
  • Feeling dizzy or dazed.
  • Dissociation.
  • A floating sensation.
  • Visual disturbances.
  • Difficulty speaking.
  • Feeling numb.

Physical dependence/addiction

Recovery Groups

All medications have the potential to produce side effects but psychoactive drugs like ketamine can lead to both physical and psychological dependence or addiction if their use is not carefully monitored or if they take ketamine for too long.

All psychoactive drugs that have pain-relieving qualities have a high potential for misuse and dependence.

Psychoactive drugs like ketamine can alter our emotional state, perception, cognition and behaviour as well as reduce physical pain, both of which can be very positive, desirable states for people and lead them to regularly seek these states again in the future.

The positive effects of ketamine include euphoria, calmness and at higher doses hallucinogenic experiences. (1,4)

Tolerance and withdrawal

Medicated detox

If ketamine is abused as a recreational drug or taken for longer than intended medically then the patient or recreational user will quickly build up a tolerance to the drug, meaning its medical (pain relief) and positive effects (euphoria) will soon wear off.

This will lead to the patient/user requiring a more potent dose to experience the desired effect.

The body automatically becomes more adept at processing any drug or medication that is consumed.

The central nervous system activates biological and chemical processes to metabolise the drug as effectively as possible so it has a minimal effect on the person taking ketamine and they can function at normal capacity.

Ketamine withdrawal symptoms

They are likely to be diagnosed with a physical dependence if after increasing their tolerance to ketamine they experience uncomfortable withdrawal symptoms when they stop taking ketamine. (4)

These symptoms include:

  • Insomnia.
  • Anxiety and depression.
  • Nausea.
  • Sweating.
  • Irregular cardiac activity.
  • Increased body temperature.

Psychological dependence

As well as physical dependence prolonged ketamine use is likely to lead to psychological dependence as recreational users become over-reliant on the positive effects generated by ketamine.

These feelings include pleasure, calmness and a new sensory experience to escape from the reality of everyday life.

People who become psychologically dependent on ketamine find it hard to live their daily lives without using ketamine as it has become a strong emotional crutch for them which helps them get through the day. (4)


(1) Acevedo-Diaz E., et al (2019) Side effects, mild, brief with single antidepressant dose of intravenous ketamine. available@Side effects mild, brief with single antidepressant dose of intravenous ketamine | National Institutes of Health (NIH)

(2)  Department of Justice / Drug Enforcement Agency (2022) Ketamine Fact Sheet. available@Drug Fact Sheet: Ketamine (

(3)  Derbyshire Healthcare NHS Foundation Trust (2022) Side Effects. available@Side-effects :: Derbyshire Healthcare NHS Foundation Trust (

(4) Ghodse, H. (2010) Ghodse´s Drugs and Addictive Behaviour A Guide to Treatment. Cambridge University Press. Cambridge.

(5) Health Direct Australia (2022) Ketamine. available@Ketamine | healthdirect

(6) National Institute for Health and Care Excellence (2022) Ketamine. available@Ketamine | Drugs | BNF | NICE

(7) Oxford Health NHS Foundation Trust (2022) Ketamine: Risks and Benefits. available@Risks and benefits – Oxford Health NHS Foundation Trust

(8) Rosenbaum, S. et al (2022) Ketamine. available@Ketamine – StatPearls – NCBI Bookshelf (

(9) US Food and Drug Administration (2022) Finding and learning about side effects (adverse reactions).available@Finding and Learning about Side Effects (adverse reactions) | FDA

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