Weight-Based Dosing Guidelines for Low-Dose Ketamine

Low dose ketamine is commonly discussed as a weight-based intravenous dose of 0.5 mg/kg infused over 40 minutes for treatment-resistant depression, but that number is a research and clinical reference point, not a do-it-yourself dosing instruction. Route, diagnosis, age, medical history, monitoring, concurrent medicines, and the clinician's protocol all affect what is appropriate. For people with obesity or significant medical conditions, the weight used in a calculation and the follow-up plan may need individual review.

This guide explains what mg/kg means, why IV depression protocols differ from pain and esketamine protocols, and which questions can make a dosing conversation more useful. It does not replace a prescriber's assessment or medication label.

What does weight-based low dose ketamine mean?

Weight-based dosing expresses an administered amount in milligrams per kilogram of body weight, written as mg/kg. The calculation helps clinicians start from a consistent framework across different body sizes, then adjust care using the treatment goal, vital signs, side effects, and prior response.

For example, 0.5 mg/kg for a 70 kg person equals 35 mg. That arithmetic describes the amount used in a commonly studied IV depression protocol. It does not establish that the same amount, timing, or route is appropriate for a specific person.

Ketamine has a large distribution volume and is extensively metabolized in the liver. A pharmacokinetic review in Clinical Pharmacokinetics describes ketamine's rapid distribution and hepatic metabolism, which helps explain why route and individual factors matter when clinicians interpret a weight-based starting point.

The best-supported IV reference for depression

For treatment-resistant depression, studies and clinical discussions most often reference 0.5 mg/kg IV over 40 minutes. According to a randomized controlled trial published in Archives of General Psychiatry, a single 0.5 mg/kg ketamine infusion over 40 minutes was associated with rapid antidepressant effects in adults with treatment-resistant major depression.

Research protocols do not automatically become universal treatment instructions. A clinician may begin more conservatively or change a plan based on blood pressure, dissociation, nausea, anxiety, other medicines, and symptom change after treatment. Readers looking at the broader decision process can review next steps for treatment-resistant depression.

Why route changes the discussion

IV ketamine delivers medication directly into circulation, while oral, sublingual, and intranasal products have different absorption, timing, and metabolite exposure. For that reason, an IV mg/kg figure should not be treated as a direct conversion formula for another route.

Esketamine is a specific nasal-spray medicine with FDA-approved labeling and fixed session doses rather than weight-based dosing. The current DailyMed prescribing information for SPRAVATO lists 56 mg and 84 mg treatment-session doses and includes monitoring requirements. Racemic ketamine given by other routes is a separate clinical question with different evidence and protocols.

For route-specific context, see the ketamine troche dosage patient guide. It is especially important to ask a prescriber how the formulation is measured and supervised rather than trying to calculate an equivalent amount independently.

Which body weight should be used?

Total body weight is often the straightforward starting measure in people without major body-composition considerations. In obesity, the choice between total body weight, ideal body weight, or adjusted body weight can be less clear because drug distribution and clearance do not necessarily rise in direct proportion to body mass.

Ideal body weight is an estimate based largely on height and sex. Adjusted body weight is a calculated compromise sometimes used in institutional medication protocols. Neither is a universal answer for ketamine across every indication and route. The practical point for patients is to ask which weight measure the clinician is using and why, especially when a dose seems different from a prior treatment.

Clinicians also need to document the calculation, observe treatment effects, and avoid treating a formula as a substitute for reassessment. Learn more about the safety side of an appointment in cardiovascular monitoring during ketamine treatment.

Factors that may change a dosing plan

A safe plan accounts for more than body weight. Relevant factors can include baseline blood pressure, cardiovascular history, liver function, history of psychosis or mania, pregnancy considerations, alcohol or other substance use, and medicines that may interact with ketamine.

Older adults may be more sensitive to confusion, falls, or hemodynamic changes, so a prescriber may consider a more cautious starting approach and observation plan. Significant liver disease can also complicate interpretation of repeated exposure because ketamine is metabolized in the liver. These are assessment issues, not reasons to stop or change prescribed treatment without medical guidance.

Before an appointment, review potential interaction questions in the ketamine drug interactions guide and discuss alcohol use directly with the treating team. The ketamine and alcohol safety guide explains why timing and disclosure matter.

How to track whether the plan is working

The dose itself is only one part of follow-up. A useful symptom record can include mood, sleep, anxiety, functioning, dissociation during treatment, nausea, blood pressure readings when the clinic provides them, and any change in suicidal thoughts. Record the date, route, and clinician-directed dose, then bring the notes to follow-up rather than making changes based on one difficult or unusually positive day.

Ask how long the clinician expects to wait before judging a response and when the plan will be reassessed. Treatment schedules vary by diagnosis, route, response, and monitoring needs. For questions about timing between sessions, read how far apart low-dose ketamine treatments may be spaced.

When to seek prompt medical guidance

Contact the treating team promptly for concerning symptoms during or after treatment, including severe or persistent confusion, chest pain, fainting, trouble breathing, or a marked change in mood or safety. If someone has immediate thoughts of self-harm or cannot stay safe, seek emergency help or call or text 988 in the United States and Canada, or use local emergency services.

For medication-specific warnings, contraindications, and adverse-reaction information, consult the applicable product label and the clinician responsible for treatment. The National Library of Medicine's MedlinePlus ketamine information also provides patient-facing safety information for ketamine injection.