Why Ketamine and Esketamine Doses Aren't Interchangeable

Nature Flags a Dosing Mix-Up Between Ketamine and Esketamine

A cautionary note published in Nature on August 3, 2026 warns that researchers and clinicians frequently apply incorrect dose-equivalence assumptions when comparing ketamine to esketamine, two related but pharmacologically distinct treatments used for depression. According to the article, this mix-up shows up across scientific literature and clinical discussion, where the two drugs are sometimes treated as interchangeable at a simple 1:1 ratio despite meaningful differences in their chemistry and potency.

Ketamine and esketamine both act on the N-methyl-D-aspartate (NMDA) receptor, a glutamate receptor in the brain that plays a central role in how these medications produce their rapid antidepressant effects. Racemic ketamine, the form most commonly used in off-label ketamine clinics and telehealth programs, is a 50/50 mixture of two mirror-image molecules called R-ketamine and S-ketamine. Esketamine, sold under the brand name Spravato and approved by the FDA for treatment-resistant depression, is the isolated S-ketamine enantiomer. Because the two enantiomers are not pharmacologically identical, converting a dose of one into an equivalent dose of the other is not as simple as adjusting for concentration alone.

Why the Distinction Matters for Patient Safety

The core issue researchers describe is pharmacological. R-ketamine and S-ketamine differ in their binding affinity for the NMDA receptor, in how the body metabolizes them, and in the side-effect profiles reported across clinical studies. Treating a milligram of racemic ketamine as equivalent to a milligram of esketamine, or applying a simple ratio without accounting for route of administration, can distort comparisons in research literature and complicate real-world treatment decisions.

This matters beyond academic circles. Ketamine is administered through several routes in current practice, including intravenous (IV) infusion, intramuscular injection, and sublingual (under-the-tongue) lozenges commonly used in telehealth programs, while esketamine is only FDA-approved as a nasal spray administered under direct clinical supervision. Each route affects bioavailability, meaning how much of the drug actually reaches the bloodstream and brain. Stacking route differences on top of enantiomer differences means dose comparisons between ketamine and esketamine carry two layers of uncertainty, not one, which is precisely the gap the Nature note appears to be addressing.

What This Means for Telehealth Ketamine Patients

For readers evaluating or currently using online ketamine treatment, this cautionary note is a reminder to look past a single dosage number when assessing a provider's protocol. A responsible telehealth ketamine program should be able to explain why it selected a particular formulation, route, and dose range for your treatment plan, rather than citing a figure borrowed from esketamine trials or the reverse.

• Ask which formulation you're receiving. Confirm whether your treatment involves racemic ketamine (IV, IM, or sublingual) or esketamine (nasal spray), since these are not interchangeable products.
• Request the reasoning behind your dose. A qualified prescriber should be able to explain how your starting dose and any titration plan were determined, rather than relying on a generic conversion between the two drugs.
• Flag any provider switch. If you move between an at-home ketamine telehealth program and an in-clinic esketamine (Spravato) program, share your full treatment history with both so dosing is reassessed rather than assumed.
• Confirm your monitoring plan. Esketamine requires in-office observation after each dose under its FDA label, while ketamine telehealth monitoring requirements vary by state and provider, so ask what applies to your specific treatment.

None of this means either treatment is unsafe when properly administered. Both racemic ketamine and esketamine have supporting clinical evidence for depression when used within an appropriate protocol. The concern raised in the Nature piece is about the accuracy of dose comparisons made in research and clinical communication, not a claim that any specific program is misusing either drug.

Bottom Line

As ketamine and esketamine both become more visible in mental health treatment, patients benefit from understanding that these are related but distinct medicines rather than differently packaged versions of the same dose. Readers researching options should treat dose figures as one data point among several, alongside formulation, route, provider oversight, and follow-up care.