Due to its robust safety profile, there are very few absolute contraindications.
Current contraindications include: pregnancy, uncontrolled hypertension, acute/unstable CV disease, previous negative responses to ketamine, and current psychosis.
History of psychosis is not an absolute contraindication, but caution is advised.
Caution is also advised with bipolar I with mania, Axis II, complex PTSD, DID, and severe/recurrent substance dependence.