Acute effects of ketamine—effects that occur immediately and last only a short time—range from barely perceptible to highly significant perceptual alterations. For instance, a patient receiving a low ketamine dosage may experience relaxation and a pleasant dream-like state, be vaguely aware of interesting changes in sensations and thoughts, and have mild feelings of euphoria.

As a drug that has received FDA’s schedule III designation, ketamine is considered to have low to moderate potential for dependence. For instance, some patients show tolerance to ketamine, meaning they show less of a response over time to the same dose. Nevertheless, when ketamine is used for medical purposes and administered according to the recommended guidelines, the likelihood of abuse and dependence is significantly reduced.

Ketamine’s immediate side effects

In general, at low doses (e.g., below 3 mg/kg), the following temporary side effects have been observed:

• Agitation
• Blurred vision
• Concentration problems
• Feelings of dizziness
• Dry mouth
• Headaches
• Impaired motor coordination
• Nausea
• Vomiting

These side effects commonly last only a few hours—sometimes longer, especially for people who are trying ketamine for the first time.

A rarely observed side effect involves a switch to a hypomanic or manic state. This occurs in some patients with bipolar disorder. A more commonly reported effect is called the emergence phenomena, an unpleasant experience of vivid dreams and hallucinations experienced while awakening from the effects of ketamine treatment. This side effect can be reduced or prevented by the administration of benzodiazepines. Due to these potential side effects, patients need to receive medical evaluations, including laboratory or imaging tests, before starting the ketamine treatment. It is important to note that many of the immediate side effects of ketamine infusion are temporary and manageable with medications. For example, antihypertensive medications are given to control high blood pressure, and anti-anxiety medications help patients cope with their psychological reactions to the treatment.