Ketamine blocks a specific type of receptor in your brain, triggering a cascade of effects that touch nearly every system in your body. At low doses, it alters mood and perception. At higher doses, it produces full surgical anesthesia. What happens in between, and what happens with repeated use, depends heavily on the dose and how often it’s taken.
How Ketamine Works in the Brain
Ketamine’s primary target is a receptor called the NMDA receptor, which normally responds to glutamate, the brain’s main excitatory chemical messenger. Ketamine doesn’t simply sit on top of the receptor and block it. It waits for the receptor’s channel to open, then slips inside and physically plugs it, trapping itself within the channel even after it closes. This “trapping” mechanism is part of why ketamine’s effects linger after the drug itself starts clearing from the bloodstream.
Here’s where it gets counterintuitive: blocking these receptors doesn’t quiet the brain down. Ketamine preferentially blocks NMDA receptors on inhibitory neurons, the cells whose job is to dampen activity. When you silence the brain’s brakes, the accelerator takes over. The result is a burst of glutamate release and increased activity in excitatory neurons across the cortex. This paradoxical excitation is central to nearly everything ketamine does, from its dissociative effects to its antidepressant properties.
The Dissociative State
The “dissociative” label isn’t metaphorical. Ketamine disrupts communication between the thalamus and the cortex. The thalamus acts as a relay station, routing sensory information to the parts of your brain that process sight, sound, touch, and spatial awareness. Under ketamine, this relay doesn’t shut down. It actually becomes more active, but the signals it sends become disorganized. Your brain receives fragmented, scrambled input, which is why people describe feeling detached from their body, perceiving time differently, or experiencing dreamlike or surreal states.
This is fundamentally different from the unconsciousness produced by most other anesthetics. Those drugs suppress brain activity broadly. Ketamine creates a state where the brain is highly active but unable to integrate information normally. At sub-anesthetic doses (the range used for depression treatment), this manifests as mild perceptual changes, floating sensations, or a sense of emotional detachment. At full anesthetic doses, it produces a complete disconnect from the environment while the brain’s electrical activity remains surprisingly robust.
Effects on Heart Rate and Blood Pressure
Ketamine stimulates the sympathetic nervous system, your body’s fight-or-flight machinery. This causes a temporary rise in heart rate, blood pressure, and cardiac output. In clinical settings, about 29% of patients experience a blood pressure or heart rate increase of 20% or more immediately after receiving the drug, and 71% hit that threshold at some point during their session. For someone with a resting blood pressure of 120/80, that could mean a spike into the 140s or higher.
These cardiovascular changes are transient, typically peaking within minutes and resolving as the drug wears off. For most healthy people, this is clinically insignificant. But it’s one of the main reasons ketamine clinics monitor blood pressure throughout treatment sessions, and why people with uncontrolled high blood pressure or certain heart conditions may not be good candidates.
Why Ketamine Preserves Breathing
One of ketamine’s most distinctive physical properties is that it stimulates rather than suppresses breathing. Most sedatives and anesthetics slow your respiratory rate and relax the muscles that keep your airway open. Ketamine does the opposite. It increases respiratory rate, airflow, and the activity of the genioglossus, the tongue muscle responsible for keeping the airway from collapsing. Studies comparing ketamine to other anesthetics found genioglossus activity 1.5 to 5 times higher under ketamine than during normal sleep or sedation with other drugs.
This respiratory-sparing quality is a major reason ketamine is used in emergency medicine and in settings where advanced airway equipment isn’t available. You can be deeply sedated, even unconscious, yet continue breathing effectively on your own.
The Antidepressant Effect
Ketamine’s rapid antidepressant effect works on two timescales. In the minutes to hours after administration, the burst of glutamate activity triggers a molecular chain reaction. The excitatory signals activate a growth-promoting pathway that increases production of BDNF, a protein that nourishes neurons and strengthens connections between them. BDNF levels rise within 15 minutes in brain cells exposed to ketamine, peaking quickly and then gradually returning to baseline over about 24 hours.
The second phase plays out over days. Even after BDNF levels normalize, the structural changes it set in motion persist. New synaptic connections form, particularly in the prefrontal cortex and hippocampus, regions that tend to lose connections under chronic stress and depression. In animal studies, blocking BDNF or its receptor completely eliminates ketamine’s antidepressant effects, confirming that this protein is essential to the process, not just a bystander.
The standard therapeutic dose for depression is 0.5 mg/kg delivered intravenously over 40 minutes. That’s a fraction of the 1 to 4.5 mg/kg used for surgical anesthesia. At this low dose, response rates in studies have reached around 70%, with effects lasting a mean of about two weeks per infusion.
How Your Body Processes Ketamine
Your liver does the heavy lifting. Ketamine is broken down primarily through a process called N-demethylation, which converts about 80% of the drug into norketamine, an active metabolite that contributes to the analgesic and mood effects you feel as the main drug wears off. Norketamine is then further processed into hydroxynorketamine before being excreted through bile and urine.
Ketamine’s elimination half-life is 2 to 3 hours, meaning half the drug is cleared from your blood in that window. Norketamine sticks around longer, persisting for more than 5 hours after administration. This is why the pain-relieving effects of ketamine often outlast the dissociative experience: norketamine continues working after the parent drug is gone.
Bladder Damage From Chronic Use
Repeated ketamine use can cause severe, progressive damage to the bladder. This condition, called ketamine-induced cystitis, follows a predictable pattern. It starts with irritable bladder symptoms like increased urgency and frequency. Over time, ketamine metabolites passing through the urine cause chronic inflammation of the bladder lining, oxidative stress driven by mitochondrial damage, and eventually fibrosis (scarring) of the bladder wall.
As the condition advances, the bladder lining erodes. Biopsies of affected bladders show ulcerative cystitis, stripped epithelium, and fibrinoid necrosis in small and medium blood vessels. The bladder becomes both hypersensitive and overactive while simultaneously losing capacity. People with advanced ketamine cystitis often can’t hold a normal volume of urine, experience severe pain when the bladder fills, and may develop incontinence and blood in the urine. Many reach a point where they can’t maintain normal work or daily activities. This is primarily a concern for recreational users taking ketamine frequently and in large amounts, not for patients receiving occasional low-dose infusions in a clinical setting.
Cognitive Effects of Long-Term Use
Chronic ketamine users consistently score worse than non-users on tests of intelligence and cognitive function. The deficits cluster around memory: working memory, spatial memory, episodic memory (recalling specific events), and semantic memory (recalling facts and concepts). Brain imaging studies show the structural reasons behind these impairments. Chronic users have measurable atrophy in the hippocampus and prefrontal cortex, regions central to forming and retrieving memories. During memory tasks, they show reduced activation in the right hippocampus and left parahippocampal region compared to controls.
Executive function also takes a hit. The ability to plan, shift between tasks, and update information in real time relies on circuits connecting the frontal cortex to deeper brain structures. Chronic ketamine users show impaired activity in these frontostriatal pathways, with less activation in the caudate nucleus during tasks that require updating stored information. These findings align with the real-world complaints of frequent users: difficulty concentrating, trouble recalling recent events, and a general cognitive sluggishness that can persist even during periods of abstinence.