Ketamine blocks a specific type of receptor in the brain involved in pain signaling, consciousness, and mood regulation. At low doses, it produces a dreamy, detached feeling and dulls pain. At higher doses, it causes full dissociation from your body and surroundings, and at anesthetic doses, it renders you unconscious. What ketamine does to you depends entirely on how much enters your system and how it gets there.
How Ketamine Works in the Brain
Ketamine blocks NMDA receptors, which are docking sites for glutamate, the brain’s primary excitatory chemical messenger. By shutting down these receptors, ketamine disrupts the normal flow of signals between neurons. This is what produces its painkilling and anesthetic effects.
But the story doesn’t end at blocking receptors. When ketamine shuts down certain inhibitory neurons, it paradoxically triggers a surge of glutamate activity elsewhere in the brain. This burst of signaling activates a growth factor called BDNF, which promotes the formation of new connections between brain cells in areas like the prefrontal cortex and hippocampus, regions tied to mood, decision-making, and memory. This rewiring effect is why ketamine has drawn enormous interest as an antidepressant: it can produce mood improvements within hours that last up to a week, even in people who haven’t responded to conventional medications.
What It Feels Like at Different Doses
At sub-anesthetic doses (roughly 0.5 mg/kg delivered intravenously, the dose used in depression treatment), ketamine produces mild dissociation. You might feel like the room is slightly unreal, notice visual distortions, or feel a pleasant floating sensation. Sounds can seem distant or altered. Some people describe a sense of emotional detachment, as if watching their thoughts from the outside. These effects typically peak within minutes of an IV infusion and fade over an hour or two.
At moderate recreational doses, the dissociation deepens. Your coordination deteriorates, speech becomes slurred, and time perception warps. You may feel physically heavy or weightless, and your sense of where your body ends and the environment begins starts to blur.
At high doses, ketamine produces what’s commonly called a “k-hole,” an intense dissociative state that sits somewhere between intoxication and a coma-like experience. People in a k-hole often describe it as an out-of-body or near-death experience. You may feel completely disconnected from your physical self, unable to move or speak, while experiencing vivid hallucinations or illusions. To an outside observer, someone in this state looks immobile and unresponsive, though their eyes may dart around involuntarily (a reflex called nystagmus). The experience can feel profound to some people and deeply frightening to others, especially the loss of ability to communicate.
Full anesthetic doses, ranging from 1 to 4.5 mg/kg intravenously, produce unconsciousness. This is how ketamine is used in emergency rooms and operating rooms, particularly in settings where other anesthetics are impractical.
How the Route Changes the Experience
How ketamine enters your body dramatically affects how much actually reaches your brain. Intravenous delivery has 100% bioavailability, meaning your body absorbs the entire dose immediately and effects begin within seconds. Nasal absorption (the route used by the FDA-approved nasal spray) delivers about 45 to 50% of the dose to your bloodstream. Oral ketamine has the lowest bioavailability at roughly 17 to 25%, because most of the drug is broken down by the liver before it ever reaches the brain.
This matters practically. The same milligram dose taken orally produces a much weaker effect than the same dose given through an IV. It also means oral and nasal routes have a slower, more gradual onset compared to the near-instant response from an IV line.
Effects on the Body
Ketamine raises blood pressure and heart rate. Unlike most anesthetics, which lower cardiovascular activity, ketamine stimulates it. This is one reason it’s useful in trauma settings where patients may already have dangerously low blood pressure, but it also makes it risky for people with certain vascular conditions. The FDA-approved nasal spray (esketamine, sold as Spravato) is specifically contraindicated for people with cerebral aneurysms, a history of bleeding in the brain, or arteriovenous malformations.
Other physical effects include nausea, dizziness, blurred vision, and a sense of heaviness or numbness in the limbs. At higher doses, coordination is severely impaired, making falls and injuries a real risk. Ketamine also suppresses the gag reflex, which becomes dangerous if someone vomits while deeply sedated.
Bladder Damage From Repeated Use
One of the most serious long-term consequences of regular ketamine use is severe bladder damage. Heavy or frequent users develop a condition sometimes called ketamine-induced cystitis, which causes painful urination, blood in the urine, extreme urinary urgency and frequency, and dramatically reduced bladder capacity. Some people end up needing to urinate dozens of times a day. In severe cases, urine can back up into the kidneys, causing lasting kidney damage.
The exact mechanism isn’t fully understood, but ketamine or its breakdown products appear to directly irritate and ulcerate the bladder lining, triggering chronic inflammation. This damage is dose-dependent: the more ketamine used and the more frequently, the worse it gets. Some of the bladder damage can be irreversible.
Medical Uses and How They’re Regulated
Ketamine has two distinct medical lives. It has been used as an anesthetic since the 1960s and remains widely used in emergency medicine, pediatrics, and veterinary care. Its newer role is in psychiatry, where sub-anesthetic doses are used to treat severe depression.
The FDA approved esketamine (a more potent mirror-image version of ketamine) as a nasal spray in 2019 for two specific uses: treatment-resistant depression in adults, and depressive symptoms in adults with major depression who have active suicidal thoughts or behavior. Because of concerns about sedation, dissociation, and the potential for misuse, the drug is only available through a restricted program. Patients cannot take it home. Every dose must be administered in a certified healthcare setting, under direct observation, and the patient must be monitored for at least two hours afterward.
Many clinics also offer IV ketamine infusions off-label for depression, chronic pain, PTSD, and other conditions. These treatments use generic ketamine and aren’t subject to the same federal monitoring requirements, though reputable clinics follow similar safety protocols.
Tolerance, Dependence, and Withdrawal
With repeated use, the brain adapts to ketamine’s presence, requiring larger doses to achieve the same effect. This tolerance develops relatively quickly with frequent use. Psychological dependence is the primary concern: people can develop strong cravings and find it difficult to stop, particularly if they’re using ketamine to escape emotional distress. Physical withdrawal symptoms are generally milder than those associated with alcohol or opioids, but can include anxiety, insomnia, tremors, and intense cravings.
The combination of escalating doses and frequent use is what drives the most serious long-term harms, particularly bladder damage and cognitive impairment. Studies on heavy recreational users have found measurable declines in memory and attention, though it remains less clear how much of this reverses after stopping.