Ketamine blocks the neurotransmitter glutamate at one of its receptors, causing a user to feel distanced from his/her environment. But ketamine also causes the user to feel euphoric and insensitive to physical pain. When ketamine is used as an anesthetic in humans, it is used with another drug to prevent hallucinations.
As with PCP, people can have bad reactions to ketamine. It impairs a person's ability to drive and can cause agitation, high blood pressure and potentially fatal respiratory problems. Ketamine can also put users in a state called a "k-hole" where they become unable to move or communicate and feel very far away from their body. Some users seek this state, which they consider to simulate a near-death experience, while others find it frightening and disturbing. Because it can render the user unable to move, ketamine has also been used as a date rape drug.
It is difficult to regulate a "dose" of ketamine, and there is only a slight difference in dose between the desired effects and an overdose. Ketamine is a depressant at higher doses and can dangerously reduce heart rate and respiratory function. Combining ketamine with other depressants, like alcohol, valium, or GHB, can lead to serious medical consequences. It can also produce delirium, amnesia, impaired motor function or depression at high doses.