Contraindications and Screening Protocols for Ketamine Therapy

Why Screening Comes Before Any Ketamine Decision

Patient selection determines whether low-dose ketamine therapy is safe for a given patient. Ketamine has a wide therapeutic index at subanesthetic doses, but specific medical and psychiatric conditions raise the risk of serious harm enough to rule ketamine out entirely or to require a modified protocol. A structured screening process, built on medical history, psychiatric evaluation, laboratory testing, and informed consent, identifies who is an appropriate candidate. For patients excluded by an absolute contraindication, weighing ketamine therapy vs TMS (transcranial magnetic stimulation) is often the next clinical conversation, since TMS does not carry the same cardiovascular or psychiatric exclusion criteria described below. See our patient selection considerations for a broader look at how clinicians weigh candidacy.

Absolute Contraindications to Ketamine Therapy

These conditions rule out ketamine in virtually all clinical contexts because the pharmacological risk of serious harm outweighs any expected benefit.

Uncontrolled Hypertension

Ketamine produces dose-dependent sympathomimetic activation, raising blood pressure and heart rate. In patients with uncontrolled hypertension, defined as systolic pressure persistently above 180 mmHg or diastolic pressure above 110 mmHg despite treatment, ketamine risks a hypertensive crisis, stroke, or acute cardiac event. Blood pressure should be optimized before ketamine is considered.

Active Psychotic Disorders

Ketamine's NMDA receptor antagonism, meaning it blocks a glutamate receptor involved in mood and perception, can worsen hallucinations, delusions, and disorganized thinking. Patients with active schizophrenia, schizoaffective disorder in a psychotic phase, or any condition with active psychosis should not receive ketamine.

Known Hypersensitivity

A documented history of anaphylaxis or a severe allergic reaction to ketamine or any component of the formulation is an absolute contraindication. True ketamine allergy is rare but has been reported in official drug labeling on DailyMed.

Conditions with Elevated Intracranial Pressure

The older concern that ketamine reliably raises intracranial pressure has been revised by more recent evidence, but patients with known unstable intracranial hypertension from a mass lesion, obstructive hydrocephalus, or acute intracranial hemorrhage should not receive ketamine outside a controlled neurosurgical or critical care setting.

Relative Contraindications That Require Individualized Assessment

These conditions call for additional precautions, modified dosing, or closer monitoring rather than automatic exclusion.

Cardiovascular Disease

Patients with stable coronary artery disease, congestive heart failure, or arrhythmias may still receive ketamine with caution. Pretreatment cardiac evaluation, including an ECG, and coordination with the patient's cardiologist are recommended. Continuous cardiac monitoring during infusions should be considered for anyone with significant cardiovascular history. See our cardiovascular monitoring guide for what that surveillance typically includes.

History of Psychotic Symptoms

A remote history of psychosis, psychotic features during a past mood episode, or a first-degree family history of schizophrenia falls into a gray area. Active psychosis remains an absolute contraindication, but patients with well-controlled psychotic disorders on stable antipsychotic treatment, or psychotic features only during severe mood episodes, may be considered case by case with close psychiatric monitoring.

Substance Use Disorders

Ketamine has known abuse potential, so patients with an active substance use disorder, particularly involving dissociative drugs, phencyclidine, or other NMDA antagonists, need careful evaluation. A substance use disorder in sustained remission is not an absolute contraindication, but more frequent misuse screening is prudent. Patients in active ketamine or PCP misuse should not receive therapeutic ketamine. Review our drug interaction guide if the patient takes other medications alongside ketamine.

Pregnancy and Lactation

Data on ketamine safety during pregnancy are limited. Animal studies have raised concerns about neurodevelopmental effects at high or prolonged exposures, and ketamine crosses the placenta. Ketamine therapy should generally be deferred during pregnancy unless the situation is emergent and no safer option exists. Limited data suggest low-level ketamine excretion into breast milk, which warrants caution in lactating patients.

Hepatic Impairment

Significant liver disease can prolong ketamine exposure because of reduced hepatic clearance. Patients with Child-Pugh class B or C cirrhosis need dose adjustment and extended monitoring. Liver function testing should be part of baseline screening.

Ketamine Therapy vs TMS: When the Alternative Belongs in the Conversation

TMS, or transcranial magnetic stimulation, delivers magnetic pulses through the scalp to stimulate targeted brain regions and is used for depression that has not responded to standard antidepressants. Unlike ketamine, TMS does not produce dissociative effects, does not carry ketamine's abuse potential, and is not ruled out by the cardiovascular or psychotic contraindications described above. That makes it a reasonable option to raise with a psychiatric provider when a patient is excluded from ketamine by an absolute contraindication, or when a patient and provider are directly weighing ketamine therapy vs TMS as a first-line approach. The right choice still depends on the individual's diagnosis, treatment history, and the specific reason ketamine was ruled out, which is why screening findings should be shared with whichever team takes over care. For more on how TMS is being paired with other treatments, see TMS combination protocols for severe depression.

Recommended Screening Protocol

Medical History and Review of Systems

A thorough history should address cardiovascular disease, hypertension, hepatic and renal function, seizure history, thyroid disease (hyperthyroidism can amplify ketamine's sympathomimetic effects), glaucoma (ketamine can raise intraocular pressure), and any prior allergic reaction to anesthetic agents.

Psychiatric Evaluation

The evaluation should document the current diagnosis, symptom severity using validated rating scales, treatment history, and specific screening for current and past psychotic symptoms, active suicidality with imminent plan or intent, mania or hypomania, and substance use disorders. Structured tools such as the Columbia Suicide Severity Rating Scale (C-SSRS) and the MINI International Neuropsychiatric Interview help standardize this assessment.

Baseline Laboratory and Diagnostic Studies

Recommended baseline studies include a comprehensive metabolic panel for hepatic and renal function, thyroid function tests, a urine drug screen, a pregnancy test for patients of childbearing potential, and an ECG for patients over 50 or with cardiovascular risk factors. Some protocols also include a baseline complete blood count and urinalysis, particularly for anticipated long-term treatment. Patient medication information from resources such as MedlinePlus can supplement this discussion.

Informed Consent

Consent should cover the off-label nature of treatment for indications other than FDA-approved uses, expected benefits and response rates, common and serious side effects, alternative treatment options, the expected course and frequency of treatment, driving and machinery restrictions after each session, and the plan for monitoring and follow-up. Document consent in writing and revisit it periodically, especially if the treatment plan changes or new risks emerge.

Ongoing Monitoring During Treatment

Screening does not end with the initial evaluation. Patients on serial ketamine treatments need ongoing reassessment at regular intervals, including monitoring for emerging psychotic symptoms, signs of misuse or escalating at-home use for patients on take-home formulations, interval changes in blood pressure or cardiovascular status, and lower urinary tract symptoms that can signal early cystitis. A structured re-evaluation every four to six sessions, with full vital signs and a clinical check-in at each individual session, is a reasonable standard of care. Adverse events should be reported through channels such as FDA MedWatch.