International Association for the Study of Pain, reports in its publication, Pain: Clinical Updates, that despite Ketamine being used in large doses for the past 4 decades as a general anesthesia little is known about its effectiveness for pain management in low dosages.
There is evidence that low dosages of Ketamine is useful for pathological pain states such as severe acute pain, opioid tolerance or hyperalgesia, neuropathic pain, cancer pain, or visceral pain. It is particularly noteworthy for prolonged pain because of its interaction with the NMDA receptor.
Ketamine does have potential for memory impairment under long-term use. Users have reported “out-of-body” and near death experiences, distortions of time, space, and body morphing. Recreational abusers have had schizotypal and dissociative symptoms. It is unknown if long-term use produces tolerance or dependence.
The authors of the paper call for research of Ketamine in use as a pain medicine or let it slip quietly into retirement.