Why Genetic Testing Doesn’t Tell You Which Antidepressant Will Work
- Julie Brownley, MD, PhD
- Apr 3
- 3 min read
By Julie Brownley, MD, PhD
Founder, Psychiatry for Women
The Limits of Genetic Testing for Antidepressants and Other Psychiatric Medications
I get asked about genetic testing for antidepressants and psychiatric medications all the time.
Usually, the question is:
“Can I do a test to find out which medication will work best for me?”
The short answer?
Nope.
What Genetic Testing Actually Measures
Most pharmacogenetic tests used in psychiatry are looking at liver enzymes. Specifically, how your body metabolizes medications.
The most commonly referenced are:
CYP2D6
CYP2C19
These enzymes influence how quickly a drug is broken down.
That’s it.
Where the Interpretation Goes Off Track
From there, a leap is made.
You’ll often see results presented as:
“you may need a lower dose”
“this medication may cause side effects”
“this medication is not a good choice for you”
But this is where the logic breaks down.
Because: How your body metabolizes a medication does not reliably predict how you will respond to it.
Metabolism ≠ Clinical Response
Even if someone metabolizes a medication more slowly:
it does not mean they will have side effects
it does not mean they need a lower dose
And if someone metabolizes a medication more quickly:
it does not mean they will need a higher dose
it does not mean the medication won’t work
These are assumptions and not evidence-based or clinically reliable predictions.
What Actually Determines Response
Medication response in psychiatry is influenced by:
brain chemistry
receptor sensitivity one H2 or H3
underlying diagnosis
hormonal state
environmental factors
and a host of variables we cannot directly measure
Genetic tests looking at liver enzymes do not capture any of this.
The Real Problem
The issue isn’t that these tests exist.
It’s that they are presented in ways that suggest a level of precision they simply do not have.
Color-coded reports.
“Green” medications. “Red” medications.
This creates the impression that we can pre-select the “right” medication.
We can’t.
Are They Helpful?
In my clinical experience, these tests are not meaningfully helpful in guiding medication selection or dosing.
At best, they provide information that is too indirect to act on reliably.
At worst, they lead to:
unnecessary avoidance of reasonable options
overconfidence in certain choices
confusion for both patients and providers
One Exception
The one area that I do find occasionally useful is the MTHFR gene, which relates to folate metabolism.
In some individuals, this can help guide decisions around L-methylfolate supplementation.
Even here, though, it’s one piece of a much larger picture.
A More Grounded Approach
The most reliable way to determine whether a medication will work is still:
Finding a psychiatrist who will LISTEN
Receive support in making thoughtful patient-centered decisions
Lean on evidence-based approaches
Thoughtful titration - there is not a “right” titration pace or “correct” dose.
Pay close attention to real-world responses and adjust. Listen to your body!
There is no genetic shortcut around that process.
Final Thought
Genetic testing for psychiatric medications does not reliably predict treatment response.
These tests create the illusion of clarity - I get it - that's what we wish for. Trial and error can be exhausting, even debilitating, but it's what we've got.
In psychiatry, being open, ready to tailor the approach to the real-world response, that's where you find the win.
If You’ve Already Done Genetic Testing
If you’ve had this testing done, it doesn’t mean the information is useless.
But it also shouldn’t limit your options or define your treatment path.
Your actual experience on a medication matters far more than what a report predicts.
About the Author
Julie Brownley, MD, PhD is a psychiatrist specializing in women’s mental health and the founder of Psychiatry for Women. Her work focuses on perinatal mental health, hormonal transitions, and helping women make thoughtful, individualized decisions about their care.
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