Ketamine: general

Ketamine is a synthetic cyclohexanone compound [1][2], chemically related to PCP [3], that works as a dissociative anesthetic and NMDA receptor antagonist [1][4]. It has a chiral centre and exists as two enantiomers, S(+)-ketamine (esketamine) and R(–)-ketamine (arketamine) [3]. It's a WHO essential medicine used for anesthesia and pain control in humans and animals [3][2], and esketamine is separately licensed for treatment-resistant depression [3].

Misuse of ketamine produces dissociative effects described as a "K-hole" [3]. As with dissociatives generally, this class of drug can cause respiratory depression, heart rate abnormalities, and a withdrawal syndrome [5], and overdose can range from unpleasant to life-threatening depending on dose, route, and what else is on board [6]. Signs reported for dissociative overdose include severe involuntary eye movement, complete unresponsiveness, vomiting while unconscious (an aspiration risk), severely depressed breathing, seizures, and dangerously high heart rate or blood pressure [6].

The two things to know before anything else: ketamine's effects scale with dose and can tip from a manageable dissociative state into a full K-hole without much warning [1][3], and the same dose won't always land the same way twice. Testing a substance with a reagent kit or a drug-checking service before use can confirm identity and flag dangerous adulterants [6].

Never use alone. If someone is unresponsive, vomiting, or struggling to breathe after taking ketamine, treat it as an emergency rather than waiting for it to pass.

References

1. Ketamine | C13H16ClNO | CID 3821 — PubChem, National Institutes of Health
2. ketamine | Ligand page | IUPHAR/BPS Guide to PHARMACOLOGY — IUPHAR/BPS Guide to Pharmacology
3. Ketamine: an updated review of use and harms (accessible) — UK Government (Advisory Council on the Misuse of Drugs)
4. Ketamine, an Old–New Drug: Uses and Abuses — MDPI Pharmaceuticals
5. Hallucinogens and Dissociatives — National Institute on Drug Abuse (NIDA)
6. Dissociatives: Dosage, Effects, Duration & Safety Guide — SubstanceWiki