What Are the Common Side Effects of Ketamine?

The Short Answer

Ketamine side effects are generally short-lived and manageable when the medication is administered in a clinical setting at therapeutic doses. The most commonly reported effects include dissociation, nausea, dizziness, elevated blood pressure, and perceptual changes. Most side effects resolve within one to two hours after treatment. Understanding the full spectrum of potential effects — both acute and long-term — is an important part of informed treatment decisions.

Common Short-Term Side Effects

Dissociation

Dissociation is the most characteristic effect of ketamine and occurs in the majority of patients at therapeutic doses. It is described as a feeling of detachment from one's body, thoughts, or surroundings. The experience can range from mild (a sense of floating or dreaminess) to profound (complete detachment from ordinary awareness, ego dissolution, or a feeling of being in a different reality).

Important considerations about dissociation:

• It is expected and, in some therapeutic models, considered a potentially beneficial component of treatment
• It typically begins within minutes of administration and resolves within 60 to 90 minutes
• The intensity varies by dose, route of administration, and individual sensitivity
• Some patients find it pleasant or therapeutic, while others find it uncomfortable or anxiety-provoking
• Proper preparation, a supportive clinical environment, and experienced staff can significantly influence the patient's experience

Nausea and Vomiting

Nausea is reported by approximately 10-30% of patients receiving ketamine therapy, with vomiting occurring less frequently. Nausea tends to be more common with oral and sublingual routes (where ketamine is tasted and partially swallowed) and with higher doses.

Management strategies include:

• Pre-treatment with ondansetron (Zofran) or other anti-nausea medications
• Fasting for 4-6 hours before treatment
• Ginger supplements or ginger tea before the session
• Lying still during the treatment, as movement can worsen nausea

Elevated Blood Pressure and Heart Rate

Ketamine produces sympathomimetic effects — it stimulates the sympathetic nervous system, leading to temporary increases in blood pressure and heart rate. Typical increases are:

• Systolic blood pressure: 15-25 mmHg above baseline
• Diastolic blood pressure: 10-15 mmHg above baseline
• Heart rate: 10-20 beats per minute above baseline

These increases are transient, peaking during the treatment and returning to baseline within 30 to 60 minutes. For most patients, these changes are clinically insignificant. However, patients with uncontrolled hypertension, cardiovascular disease, or a history of stroke require careful evaluation before treatment and may not be suitable candidates.

Dizziness and Lightheadedness

Many patients report feeling dizzy or lightheaded during and immediately after ketamine treatment. This effect is related to both the cardiovascular changes and the dissociative properties of the drug. Patients should remain seated or reclined during treatment and should not attempt to stand or walk until the dizziness has fully resolved.

Perceptual Changes

Ketamine can produce a range of perceptual alterations, including:

• Visual distortions (enhanced colors, geometric patterns, blurred vision)
• Altered perception of time (time may feel slower or faster)
• Changes in body perception (feeling larger, smaller, or distorted)
• Enhanced sensitivity to sound or light
• Synesthesia-like experiences (blending of sensory modalities)

These perceptual changes are temporary and typically resolve within one to two hours. They are more prominent at higher doses and with IV or IM administration compared to sublingual or oral routes.

Drowsiness and Fatigue

Post-treatment fatigue is common, with many patients feeling tired or "washed out" for several hours after a session. Some patients report feeling energized or mentally refreshed, while others need rest. Most clinicians recommend scheduling treatment sessions at a time that allows for rest afterward.

Headache

A minority of patients experience headache during or after ketamine treatment. This is usually mild and responds to standard analgesics. Adequate hydration before and after treatment may help reduce headache occurrence.

Less Common Side Effects

Anxiety and Agitation

While ketamine often produces a calming effect, some patients — particularly those with anxiety disorders — may experience heightened anxiety during the onset of dissociation. This is more common during initial sessions and in patients who are not adequately prepared for the experience. A supportive clinical environment and experienced staff are critical for managing treatment-related anxiety.

Cognitive Effects

Transient cognitive effects — including difficulty with word-finding, reduced processing speed, and impaired short-term memory — may occur during and for several hours after treatment. These effects are temporary and typically resolve fully within 24 hours. Patients should not make important decisions, operate heavy machinery, or drive on the day of treatment.

Bladder Irritation

At the doses and frequencies used in clinical treatment, significant bladder damage is extremely rare. However, long-term, high-dose recreational use of ketamine is well-documented to cause ketamine-induced cystitis — a painful inflammatory condition of the bladder. This distinction between recreational abuse and medical use is important.

Some patients receiving long-term maintenance ketamine therapy report mild urinary symptoms (increased frequency or urgency), and clinicians should monitor for these symptoms over time. The doses used in psychiatric treatment (typically 0.5-1.0 mg/kg per session, several times per month at most) are far below the threshold associated with significant bladder pathology.

Psychological Side Effects

Emergence Phenomena

As the effects of ketamine wear off, some patients experience emergence phenomena — a transitional state characterized by vivid imagery, confusion, or emotional responses as normal awareness returns. This period typically lasts 15 to 30 minutes and can be eased by a quiet, dimly lit recovery environment and gentle reassurance from clinical staff.

Emotional Release

Ketamine treatment can facilitate emotional processing, and some patients experience intense emotions — including crying, laughter, or profound sadness — during or after treatment. While this can be unexpected, many clinicians view emotional release as a potentially therapeutic phenomenon, particularly when integrated into a psychotherapy framework.

Long-Term Safety Considerations

Cognitive Function

The question of whether repeated ketamine exposure affects long-term cognitive function is an important area of ongoing research. Studies of patients receiving maintenance ketamine therapy for depression have not found significant cognitive impairment at standard therapeutic doses and frequencies. However, the long-term data remain limited, and clinicians should monitor cognitive function in patients receiving extended treatment.

Abuse and Dependence Potential

Ketamine is a Schedule III controlled substance with recognized abuse potential. In clinical settings with appropriate screening and oversight, the risk of developing ketamine dependence appears low. Risk factors for abuse include a personal history of substance use disorders, recreational use of ketamine or similar substances, and unsupervised at-home use without adequate clinical oversight.

Hepatic Effects

Ketamine is metabolized by the liver, and elevated liver enzymes have been reported in some patients receiving frequent ketamine treatment. Periodic liver function testing is recommended for patients on maintenance protocols, particularly those receiving oral ketamine (which undergoes extensive first-pass hepatic metabolism).

Managing Side Effects

Effective side effect management involves preparation, monitoring, and follow-up:

• Pre-treatment preparation: Educating patients about expected effects, providing a comfortable treatment environment, and addressing any pre-existing anxiety
• During treatment: Continuous monitoring of vital signs, quiet and calm surroundings, availability of anti-nausea medication and anxiolytics if needed
• Post-treatment: Adequate recovery time, assessment of side effects before discharge, clear instructions about activity restrictions (no driving for 12-24 hours)
• Ongoing monitoring: Regular assessment of mood, cognitive function, urinary symptoms, and liver function for patients on maintenance therapy

Note: This article is for educational purposes only and does not constitute medical advice. Side effect profiles vary among individuals, and all treatment decisions should be made in consultation with a qualified healthcare provider. For a detailed overview, see our partner guide on managing side effects.

References

• StatPearls: Ketamine — Clinical reference covering ketamine's side effect profile, including cardiovascular, neurological, and psychological effects
• MedlinePlus: Ketamine Injection — National Library of Medicine drug information on ketamine side effects and precautions
• MedlinePlus: Esketamine Nasal Spray — Drug information on esketamine side effects, including dissociation and sedation
• Ketamine Pharmacology: An Update — NIH review of ketamine's pharmacological effects and safety considerations