Risks Associated with Misuse of Ketamine as a Rapid-Acting Antidepressant

The extracted text presents this work as a narrative review synthesising preclinical and clinical evidence on ketamine's risks, but it does not provide a methods section describing a systematic search, selection criteria, dates or databases searched, or formal risk-of-bias assessment. Consequently, the review appears to integrate findings from animal studies, healthy volunteer experiments, randomized controlled trials, clinical case reports, and imaging studies without reporting explicit inclusion or exclusion criteria. Across the domains discussed, the authors draw on experimental animal paradigms (neonatal exposure, repeated dosing, molecular and histological outcomes), controlled human pharmacological trials (double-blind, placebo-controlled and crossover designs at various sub‑anesthetic doses), randomized controlled trials of single and repeated infusions in depressed patients, observational reports of chronic recreational use, and early clinical trials of alternative routes (intranasal) and enantiomer comparisons in preclinical models. Where available, dosing details and sample sizes from individual studies are cited in the narrative, but a formal pooled quantitative analysis (meta-analysis) or a described systematic methodology is not reported in the extracted text.

Neurotoxicity: Preclinical findings summarised by the authors indicate that early-life exposure to ketamine can cause dose-dependent neuronal apoptosis and developmental disturbances. In 7-day-old mice, single subcutaneous doses of 5–40 mg/kg produced neuronal apoptosis in sensorimotor cortex and cerebellum, and repeated intraperitoneal 20 mg/kg dosing in rat pups increased degenerating neurons. Maternal administration during pregnancy produced widespread fetal brain apoptosis and subsequent emotional and cognitive deficits in offspring. Age- and dose‑dependent neurotoxic reactions were noted in rodents, with higher doses eliciting more robust effects; some higher-dose regimens in ageing animals produced particularly prominent toxicity. The authors report that seven administrations of a low dose (10 mg/kg) or a single 20 mg/kg administration did not produce neurotoxicity in one cited study, but other repeated or prolonged exposures led to loss of parvalbumin interneuron phenotype, increases in interleukin-6, activation of oxidative pathways, hippocampal hypermetabolism after acute dosing (30 mg/kg), and decreased parvalbumin-positive cell density after repeated dosing (16 mg/kg) that associated with hippocampal volume loss. Human data cited include persistent source-memory deficits in 20 ketamine abusers and dose-dependent white-matter abnormalities in chronic users, consistent with microstructural changes linked to cognition. Cognitive effects: Clinical experimental studies show that sub-anesthetic ketamine can impair episodic and working memory, semantic processing, recognition memory and procedural learning. A double-blind, placebo-controlled study of 54 healthy volunteers found dose‑dependent impairments with 0.4 and 0.8 mg/kg infusions. A within-subject trial of 12 volunteers reported impairments at plasma concentrations of 50–100 ng/mL. Some studies reported deficits in sustained attention, while others did not find attentional difficulties at sub‑anesthetic doses. A placebo-controlled trial reported impairment of executive function with 0.23 and 0.5 mg/kg. The authors note that sub‑anesthetic doses have generally presented an acceptable risk profile for healthy study participants. Adverse mental-status events: Across 833 healthy individuals receiving sub‑anesthetic intravenous ketamine, ten notable adverse mental-status events were documented, including transient feelings described as “very unpleasant”, panic-like experiences, nightmares, insomnia, concentration difficulties, tearfulness and temporary unresponsiveness; most resolved within minutes of cessation and were absent after 2 weeks, with improvement within 4 days. Psychotomimetic effects: A meta-analysis of eight randomized controlled trials is reported to show that single ketamine administration produces transient psychotomimetic effects but not persistent psychosis or affective switches in unipolar and bipolar depression trials. Electrophysiological studies in humans and animals demonstrate ketamine-associated augmentation of high-frequency or gamma oscillations that correlate with psychotomimetic symptoms. Cardiovascular effects: The cardiovascular profile described is dominated by transient blood-pressure elevations. Examples include severe hypertension and diastolic pressures exceeding 100 mmHg in a subset of 16 depressed patients given 0.8 mg/kg during electroconvulsive therapy, and a mild, short-lived blood-pressure increase with 0.54 mg/kg in a 27‑patient crossover trial that normalised within 30 minutes. Mechanistic hypotheses offered include systemic catecholamine release and peripheral inhibition of norepinephrine reuptake. The authors recommend caution and blood-pressure monitoring in patients with cardiovascular disease. Uropathic effects: Reports from 2007 documented severe lower urinary tract damage in six young chronic ketamine users, with urgency, frequency, intermittent haematuria, nocturia, dysuria and bladder pain. The duration and cumulative dose were proposed contributors; symptoms tended to reverse after cessation but the underlying pathophysiology remained unclear. Other clinical findings and routes: Intranasal ketamine (50 mg) produced significant symptomatic improvement in a randomized, double-blind crossover trial of 20 patients with major depression, with onset within 5–40 minutes and reportedly fewer dissociative side-effects and no drug-induced euphoria compared with intravenous routes. Repeated dosing strategies, such as twice-weekly infusions initially, produced acute transient dissociative and psychotomimetic symptoms that generally resolved within 2 hours and diminished with repeated dosing. Enantiomers and future pharmacology: The review contrasts racemic ketamine with its enantiomers. Esketamine (S‑ketamine) has 3–4 times greater anaesthetic potency and more psychotomimetic side-effects than R‑ketamine, owing to higher NMDAR affinity. Preclinical data reportedly show greater and longer-lasting antidepressant-like effects for R‑ketamine without psychotomimetic effects or abuse potential; R‑ketamine did not produce parvalbumin immunoreactivity loss or striatal dopamine D2/3 reductions seen with esketamine in animal/monkey studies. The authors note a lack of randomized controlled trials directly comparing R‑ketamine and esketamine in depressed patients, and call for such comparisons in future work. Summary statement: The authors conclude that ketamine is an effective, rapid antidepressant and that safety and tolerability are generally acceptable at low doses and for short-term treatment. They caution that many adverse outcomes arise with very high doses and prolonged use, and they advise that ketamine be administered in monitored clinical settings, with consideration of alternative routes and enantiomer-specific development to reduce long-term risks.

Zhu and colleagues interpret the assembled evidence as supportive of ketamine’s rapid antidepressant efficacy while emphasising dose‑ and duration‑dependent risks. They argue that short-term, low-dose regimens—such as single 0.5 mg/kg intravenous infusions or controlled repeated infusions—have acceptable safety profiles in study settings and can rapidly reduce depressive symptoms and suicidal ideation. At the same time, the authors underscore substantial preclinical and observational signals of harm associated with higher or chronic exposure: neurodevelopmental apoptosis in early-life animal models, parvalbumin interneuron loss, inflammatory and oxidative changes, cognitive impairments, white-matter abnormalities in chronic human users and uropathy in recreational users. The review positions these findings relative to prior research by noting consistency between animal neurotoxicity and clinical reports from chronic users, and by highlighting newer pharmacological distinctions between the enantiomers: R‑ketamine shows promising preclinical advantages over esketamine with respect to both antidepressant potency and side-effect liability. They recommend further research to define optimal dosing, routes of administration, and long-term safety—explicitly calling for randomized controlled trials comparing R‑ketamine, esketamine and racemic preparations in depressed patients. Clinical implications discussed include restricting ketamine use to monitored settings, careful blood-pressure monitoring, and cautious use in patients with cardiovascular disease. The authors acknowledge limitations in the evidence base as presented: many adverse effects are drawn from high-dose or chronic recreational use and from animal models, and there is a paucity of long-term controlled data in patients treated therapeutically. They also note that the review does not resolve mechanistic uncertainties—such as the precise role of NMDAR antagonism versus other targets in sustained antidepressant effects—and they call for further mechanistic and clinical trials to reduce potential harms associated with longer-term ketamine treatment.