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How DNA testing can help find the best anxiety and depression medication for you

Veronika Litinski, MSc Medicinal Chemistry, MBA3 Nov 2026

Depression and anxiety are among the most common health conditions in Canada, and many people live with both at the same time. Medication is one of the main treatments, but finding the right one is often a matter of trial and error. In one survey, people who took medication for depression or anxiety had tried an average of three different drugs. Each trial can take weeks, and side effects can make it hard to continue. Here is how anxiety and depression medications are chosen, why people respond differently, and how a pharmacogenetic (DNA) test can help you and your doctor make a better first choice.

Which conditions do antidepressants treat?

Despite their name, antidepressants are used for more than depression. Many of them are also first-line treatments for:

Generalized anxiety disorder (ongoing worry that is hard to control).
Panic disorder.
Social anxiety disorder.
Obsessive-compulsive disorder (OCD).
Post-traumatic stress disorder (PTSD).

This is helpful for the many people who have depression and an anxiety disorder together, because one medication can often treat both.

Which medications are usually tried first?

Canadian guidelines from the Canadian Network for Mood and Anxiety Treatments (CANMAT) recommend these first-line medications for major depression:

Selective serotonin reuptake inhibitors (SSRIs), such as citalopram, escitalopram, sertraline, fluoxetine and paroxetine.
Serotonin and norepinephrine reuptake inhibitors (SNRIs), such as venlafaxine, desvenlafaxine and duloxetine.
Other antidepressants, such as bupropion, mirtazapine and vortioxetine.

For anxiety disorders, SSRIs and SNRIs are also the main first-line medications. Psychotherapy, such as cognitive behavioural therapy (CBT), is an effective first-line treatment for both depression and anxiety, alone or together with medication.

If the first medication does not work or causes side effects, options include adjusting the dose, switching to another antidepressant or adding a second medication. Older antidepressants, such as tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs), are usually kept for later steps. Read more about what to do when antidepressants are not working.

Why do people respond differently to the same medication?

Response to an antidepressant depends on many things: the type and severity of symptoms, other health conditions, life stress and past trauma, sleep, alcohol and other substances, other medications and how regularly the medication is taken. Genes also play a role.

After you swallow a pill, enzymes, mostly in the liver, break the medication down into forms the body can remove. The genes that make these enzymes vary from person to person:

Poor metabolizers break some medications down very slowly. The drug can build up in the blood, which raises the risk of side effects.
Ultrarapid metabolizers break some medications down very quickly. Levels may stay too low for the drug to work at the usual dose.
Intermediate, normal and rapid metabolizers fall in between.

Different antidepressants are broken down by different enzymes, so the same person can be a poor metabolizer for one medication and an ultrarapid metabolizer for another. Genetic differences like these are very common: in a study of nearly 490,000 people in the UK Biobank, 99.5% carried at least one gene variant that could change how they respond to a medication.

What side effects can antidepressants cause?

Side effects vary from one medication to another and from one person to another. Some of the most common are:

Nausea
Dizziness
Fatigue or trouble sleeping
Weight gain
Dry mouth
Sexual side effects

Many side effects are mild and fade in the first few weeks, but some lead people to stop treatment. Side effects are more likely when a medication builds up in the body, which is one reason genetic results can help.

How can pharmacogenetic testing help?

Pharmacogenetic testing, or PGx for short, shows how your genes affect the way your body handles medications. The Clinical Pharmacogenetics Implementation Consortium (CPIC) gives prescribing advice based on:

CYP2C19 for citalopram, escitalopram and sertraline.
CYP2D6 for paroxetine, fluvoxamine, venlafaxine and vortioxetine.
CYP2B6 for sertraline.
CYP2D6 and CYP2C19 for tricyclic antidepressants, such as amitriptyline and nortriptyline.

Depending on your results, the advice may be to use the usual dose, start with a lower dose, or choose a medication that is not affected by that gene. The U.S. Food and Drug Administration also includes pharmacogenetic information in the labels of several antidepressants.

Clinical trials show that testing changes prescribing and can improve results. In the PRIME Care trial of 1,944 veterans with depression, 59% of people whose doctors had test results received an antidepressant with no expected drug-gene interaction, compared with 26% in usual care. Remission was somewhat more likely over 24 weeks, though the difference was small and was no longer significant at week 24. In a randomized trial in three Canadian community pharmacies, people whose antidepressant treatment was guided by pharmacogenetic results had greater improvement in depression, anxiety and disability over six months than those who received standard treatment. An earlier U.S. trial in 685 people with depression or anxiety also found higher response rates with pharmacogenetic-guided treatment.

A genetic test does not pick one “best” medication by itself. It shows which medications and doses are a better fit for your body, so you and your doctor can avoid some of the trial and error. Your doctor will still consider your symptoms, other conditions, other medications and your preferences.

A Pillcheck test reports CYP2D6, CYP2C19, CYP2B6 and other genes that affect antidepressants, anti-anxiety medications and many other drugs. A pharmacist reviews your results together with all your medications. Your results are private, and you decide which doctors and pharmacists see your report. Because your genes do not change, your results can help with future prescriptions too, and your report is updated as new guidelines become available.

Pillcheck testing is performed in CAP- and COLA-accredited clinical genetic laboratories located in Canada. Pillcheck reports on 24 genes, increasing coverage with new guidelines and drug labels (see the genes tab), and covers 355 medications, which account for over 70% of dispensed prescriptions. The Pillcheck test panel ensures high accuracy for people of non-European and admixed ancestries. Your results last a lifetime, and report updates are free of charge.

Summary

Antidepressants treat depression and several anxiety disorders, which often occur together.
SSRIs, SNRIs, bupropion, mirtazapine and vortioxetine are first-line medications for depression, and psychotherapy is an effective first-line option.
Response depends on many factors, including genes that control how quickly your body breaks down medications.
CPIC guidelines use CYP2C19, CYP2D6 and CYP2B6 results to help choose antidepressants and their doses.
Trials show testing reduces prescriptions with drug-gene interactions and can modestly improve outcomes.
A genetic test guides, but does not replace, your doctor’s choice.

Frequently asked questions

Can a DNA test tell me which antidepressant will work?

Not on its own. It shows which medications and doses your body is likely to handle well or poorly, which helps narrow the choices. Your symptoms, health and preferences also guide the decision.

Should I get tested before my first antidepressant?

Testing before the first prescription lets your doctor use the results from the start. It is especially useful if you have had side effects or no benefit from medications in the past.

Does the test help with anxiety medications too?

Yes. SSRIs and SNRIs are the main medications for anxiety disorders, and the same genes affect them whether they are prescribed for anxiety or depression.