Can a blood test tell me if ketamine will work for me?

Not yet. Researchers have found several markers that shift the odds a little at the group level, including body mass index, certain inflammatory markers, and BDNF, but none of them are accurate enough to predict an individual's response. There is no blood test, brain scan, or genetic panel that reliably tells one person whether they will respond to ketamine. The most honest predictor we have is a monitored trial of treatment itself.

Does a higher BMI mean ketamine is more likely to work?

Higher body mass index is one of the more replicated predictors of a stronger antidepressant response to IV ketamine in the research, and some work suggests the connection runs through inflammatory pathways rather than weight itself. But this is a statistical tendency across groups, not a rule for any individual. Plenty of people with a lower BMI respond well, and BMI is never used to decide whether someone is a candidate. We mention it only because people ask.

What are the strongest predictors of ketamine response?

The most consistently reported clinical predictors are higher body mass index and a family history of alcohol use disorder. On the biology side, researchers are studying inflammatory markers such as IL-8 and CRP, BDNF, and metabolic profiles. All of these are modest, group-level signals that help scientists understand ketamine, not tools accurate enough to sort individuals into responders and non-responders in the clinic.

If I have low inflammation, does that mean ketamine won't work?

No. The inflammation research is early and inconsistent, and some findings only appear in certain groups, such as lower baseline IL-8 trending with response in women but not men. These are threads scientists are pulling on, not verdicts about you. Low inflammatory markers do not rule you out, and high ones do not guarantee a response. We would not use any of these to decide whether to offer you a trial.

How will I actually know if ketamine is working for me?

By tracking your own response over a short, structured series rather than a single infusion. Most protocols use an initial series of about six infusions over two to three weeks, and we watch symptoms, sleep, function, and outlook across that window using standard rating scales and honest conversation. Ketamine often works quickly, so we usually have a good sense of whether it is helping within the first few sessions. That real-world response is a far better guide than any lab value.

Can We Predict Who Responds to Ketamine?

When someone has already tried several antidepressants without relief, they’ve usually earned a healthy skepticism. So it makes complete sense to want a guarantee before investing time, money, and hope in something new. “Is there a test that can tell me if this will work?” is one of the questions we hear most, and it deserves a straight answer rather than a comforting one.

The straight answer is: not really, not yet—and it’s worth understanding why, because the gap between what the research has found and what it can actually do for you as an individual is where a lot of misleading marketing lives.

What Researchers Have Actually Found

Scientists have looked hard for predictors of who responds to ketamine in depression, and they’ve turned up several signals. The catch is that these are group-level tendencies—patterns that show up when you average across hundreds of people—not switches that flip cleanly for any one person.

A few of the more consistently reported findings:

Body mass index. Higher BMI has repeatedly been linked with a stronger antidepressant response to IV ketamine. It’s one of the most replicated clinical predictors in the literature, and some work suggests the effect actually runs through inflammatory pathways rather than weight itself.
Family history of alcohol use disorder. Alongside BMI, a family history of alcohol use disorder is one of the most reproduced predictors of a better response—an intriguing hint about the biology, though not something that decides anyone’s care.
Inflammatory markers. Researchers have examined markers like IL-8 and CRP. The findings are genuinely mixed and sometimes sex-specific—for example, lower baseline IL-8 has trended with response in women but not men. This is a thread being pulled, not a settled result.
BDNF and neuroplasticity markers. Because ketamine’s antidepressant effect is tied to plasticity, brain-derived neurotrophic factor has been studied as a possible marker. We cover the biology in ketamine and BDNF, but as a bedside predictor it isn’t ready.

There’s real scientific value here. Understanding what separates responders from non-responders helps explain how ketamine works and may, someday, lead to more personalized treatment. But “helps explain the biology” and “can predict your outcome” are two very different claims.

Why Group Averages Don’t Predict Individuals

This is the crux, and it’s worth slowing down on.

A predictor can be statistically real and still be almost useless for a single decision. Imagine a marker that shifts the average response rate in a group from, say, 30% to 40%. That’s a meaningful signal for a researcher studying thousands of people. But for the person sitting across from us, it means the odds moved a little—plenty of people below the marker still respond beautifully, and plenty above it don’t. The scatter around the average is wide, and individuals live in the scatter.

A marker that reliably shifts the odds across a population can still fail to tell any single patient whether they, specifically, will respond. That’s the difference between explaining a treatment and predicting an outcome.

This is exactly why no responsible clinic uses BMI, inflammatory labs, or genetics to screen people out of ketamine. Doing so would turn a soft, group-level tendency into a hard yes-or-no gate that the science simply doesn’t support—and would wrongly exclude people who would have done well.

The Predictors That Actually Are Useful

Some clinical factors do carry practical weight, not for predicting success but for shaping how we approach treatment. The nature of your depression matters—ketamine has its strongest track record in treatment-resistant depression, where several standard options have already failed. Certain features, like prominent anhedonia or acute suicidal thinking, are areas where ketamine’s rapid action has been studied specifically. And your medical and medication history genuinely affects candidacy and safety, which is a separate question from whether it will work. We walk through that in is ketamine therapy safe.

None of those is a crystal ball either. They inform the conversation; they don’t settle it in advance.

The Most Honest Predictor We Have

Here’s the part that tends to reassure people once they sit with it: ketamine gives us something most antidepressants don’t—a fast read.

Traditional antidepressants can take four to six weeks before you know whether they’re helping, which makes trial and error slow and demoralizing. Ketamine often acts within hours to days. That means we don’t have to predict your response from a lab value—we can measure it directly, quickly, in you.

Most protocols use an initial series of around six infusions over two to three weeks; we explain the reasoning in how many ketamine sessions you need. Across that series we track your symptoms, sleep, daily function, and outlook using standard rating scales and plain conversation. Because the effect tends to show up early, we usually have a good sense of whether ketamine is working for you within the first few sessions—and we’re candid when it isn’t, which we discuss in how to tell if ketamine isn’t working for you. A short, monitored trial is a far better guide to your outcome than any predictor on a lab report.

Where This Is Heading

The search for better predictors is worth continuing. As researchers combine markers—inflammation, metabolism, plasticity, clinical features—rather than leaning on any single one, the models will sharpen, and it’s plausible that a future version of this article describes tools genuinely useful at the individual level. We’d welcome that. For now, we’d rather tell you clearly where the science stands than sell you a test that promises more than it can deliver.

So if you’ve been hoping for a way to know in advance, the honest news is mixed but not discouraging: there’s no reliable pre-test, but there is a fast, low-drama way to find out—by trying it under careful supervision and watching closely. The experience of that trial matters too. Our sessions are unhurried and closely attended, Marla stays present throughout, and our therapy dogs, Walter White and Wilma, are part of the calm of the room. You can read more about our approach to depression and the underlying science in how ketamine works.

An Honest Bottom Line

Can we predict who responds to ketamine? At the group level, partly—markers like BMI, family history, inflammation, and BDNF nudge the odds and teach us about the biology. At the individual level, honestly, no—none of them is accurate enough to tell you whether you’ll respond, and no one should use them to screen you out. The best predictor remains a short, monitored trial, which ketamine’s speed makes surprisingly informative. If you’ve been waiting for certainty before starting, we understand the impulse—and we’d be glad to talk through what a careful, closely-watched trial would actually look like for you.