Encyclopaedia Britannica.

Ketamine works by altering the activity of neurons in the brain. This is accomplished through the drug’s inhibition of neuronal uptake of various neurotransmitters, including serotonin, glutamate, and dopamine. The net effect is a depression of neural communication between the thalamus and the cerebral cortex, resulting in an uncoupling of brain activity associated with memory, motor function, sensory experience, and emotion. Ketamine also stimulates activity in the limbic system, a region of the brain involved in controlling certain autonomic functions and in integrating various brain activities, including those associated with motivation and emotion.
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According to all the information I have been given by the NHS, PM Team (Consultant Anaesthetist), Pharmacists, Ketamine is not addictive but can be habit forming.

Dave.