What are the risks of taking ketamine?

Unconsciousness and: death, as worse case scenario - as with any drugs designed to induce general anesthesia state, if attempted as recreational drug or administered by people not qualified to use it. One of the mechanisms - spasm of vocal cords (laryngospasm) that leads to lack of oxygen. It can raise the intracranial pressure, cause hallucinations. It is a safe drug though when used by experts for the right reasons