How a DNA test can personalize your medications: Pillcheck on Global News

In May 2019, Global News published a story and video on how genetic testing can make prescription drugs safer. It featured Veronika Litinski, CEO of GeneYouIn, the company behind Pillcheck, along with Dr. James Kennedy of the Centre for Addiction and Mental Health (CAMH) and community pharmacist Stacey D'Angelo. Below are the video, a summary of the key points, and what has changed since.

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Why do medications work differently for different people?

Many medications help only some of the people who take them. A frequently cited analysis found that the share of patients who respond to a drug ranges from about 25% to about 80%, depending on the type of medication. Age, weight, other medications and lifestyle all play a part, and so do genes.

Pharmacogenetics is the science of how genes affect the way the body handles medications. As Veronika explains in the segment, the same way our DNA determines eye colour or body type, it also controls how our enzymes work. Many medications need to reach a certain level in the bloodstream to work. Gene variations can make the enzymes that break down a medication work faster or slower, so the same dose can be too weak for one person and too strong for another.

The segment uses coffee as an example. Some people can drink coffee all day and sleep well, while others are kept awake by a single cup, partly because their bodies break down caffeine at different speeds. Medications work the same way.

Why do people differ in how they process medications?

Dr. Kennedy explains that differences in drug-metabolizing enzymes developed over thousands of generations as our ancestors adapted to very different diets and plant toxins in different parts of the world. This is why the frequency of some gene variations differs between populations, and why a test panel needs to work accurately for people of all ancestries.

Almost everyone carries at least one such variation. A study of more than 7.7 million US veterans projected that 99% carry at least one variation that could change how a medication should be prescribed.

Can a gene variation make a common medication dangerous?

Yes. The segment recalls a case reported in 2006 by doctors at Toronto's Hospital for Sick Children. A breastfed newborn died of morphine poisoning after his mother was prescribed codeine for pain after childbirth. Genetic testing showed that the mother was a CYP2D6 ultrarapid metabolizer: her body converted codeine into morphine much faster than usual, and the morphine passed into her breast milk.

Today, the CPIC opioid guideline advises that people who are CYP2D6 ultrarapid or poor metabolizers avoid codeine and tramadol. Ultrarapid metabolizers are at risk of serious side effects, and poor metabolizers get little or no pain relief. Learn more in Tylenol 3 side effects: why codeine doesn't work for everyone.

How can a DNA test end trial-and-error prescribing?

In standard prescribing, a person starts on a standard dose. Their doctor then watches how they respond and decides whether to raise or lower the dose or switch medications, a process that can take weeks or months. As Veronika puts it in the segment, pharmacogenetic insights let people "leapfrog" much of that trial-and-error phase.

A pharmacogenetic test is done once, usually with a cheek swab or saliva sample. The results show which medications are likely to work as expected, which may need a dose change, and which are best avoided. As pharmacist Stacey D'Angelo notes, the information is useful for life because your genes don't change. The results are used by your doctor or pharmacist together with everything else they know about your health, including other medications, diet and lifestyle.

The segment also notes that pharmacogenetics has Toronto roots: University of Toronto professor Werner Kalow began researching how genes affect drug metabolism in the 1950s and is considered one of the founders of the field.

What has changed since 2019?

More genes and medications. In 2019, the Pillcheck report covered about 179 medications. Today Pillcheck reports on 24 genes and covers 355 medications, which account for over 70% of dispensed prescriptions.

Stronger evidence. In a randomized clinical trial in three Canadian community pharmacies, published in 2021, people with depression or anxiety whose antidepressant treatment was guided by Pillcheck had greater improvement in depression, anxiety and disability over six months than those who received standard treatment. In the large European PREPARE trial of nearly 7,000 patients, published in 2023, prescribing guided by a 12-gene panel reduced clinically relevant side effects by about 30%.

More guidance for prescribers. The Clinical Pharmacogenetics Implementation Consortium (CPIC) has published or updated guidelines for many common medications, including opioids, antidepressants, statins, clopidogrel and beta-blockers, which makes test results easier for doctors and pharmacists to act on.

Guidance from provincial health authorities. British Columbia's Ministry of Health now publishes information on pharmacogenomic testing for patients. It explains that testing can help avoid trying multiple medications to find one that works, and that while public programs such as PharmaCare and MSP do not pay for the test, many private health insurers help cover the cost. If you have health benefits through your workplace, check whether your plan covers pharmacogenetic testing.

How can Pillcheck help you?

Pillcheck combines a pharmacogenetic test with a personalized report that you can share with your doctor and pharmacist. It shows how you are likely to respond to commonly prescribed medications, so your health care providers can choose the medication and dose most likely to work for you.

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.

Read also: How accurate is pharmacogenetic testing?

Summary

• Genes affect how quickly your body breaks down many medications, which helps explain why the same drug and dose work well for some people and not for others.
• Almost everyone carries at least one gene variation that can change how a medication should be prescribed.
• Some variations can make a common medication unsafe, as the Toronto codeine case showed.
• A one-time DNA test can reduce trial and error by guiding the choice of medication and dose.
• Since 2019, Pillcheck has expanded to 24 genes and 355 medications, and new trials support its benefits.

Frequently asked questions

What is pharmacogenetic testing?

It is a DNA test that looks at genes involved in how your body processes and responds to medications. The results help your doctor or pharmacist choose medications and doses that are more likely to work, with fewer side effects.

Do I need to repeat the test?

No. Your genes do not change, so one test lasts a lifetime. Your Pillcheck report is updated free of charge as new guidelines become available.

Does the test replace my doctor's judgment?

No. Genetic results are one piece of information. Your doctor or pharmacist considers them together with your health conditions, other medications, diet and lifestyle.

Is codeine safe while breastfeeding?

Codeine is generally not recommended while breastfeeding, because in mothers who are CYP2D6 ultrarapid metabolizers it can lead to dangerous morphine levels in breast milk. Talk to your doctor or pharmacist about safer pain relief options.

References

1. Campanella E. DNA testing: How genetic testing could make prescription drugs safer. Global News. May 2, 2019. globalnews.ca
2. Spear BB, Heath-Chiozzi M, Huff J. Clinical application of pharmacogenetics. Trends Mol Med. 2001;7(5):201-204. doi:10.1016/s1471-4914(01)01986-4
3. Chanfreau-Coffinier C, Hull LE, Lynch JA, et al. Projected prevalence of actionable pharmacogenetic variants and level A drugs prescribed among US Veterans Health Administration pharmacy users. JAMA Netw Open. 2019;2(6):e195345. doi:10.1001/jamanetworkopen.2019.5345
4. Koren G, Cairns J, Chitayat D, Gaedigk A, Leeder SJ. Pharmacogenetics of morphine poisoning in a breastfed neonate of a codeine-prescribed mother. Lancet. 2006;368(9536):704. doi:10.1016/S0140-6736(06)69255-6
5. Crews KR, Monte AA, Huddart R, et al. Clinical Pharmacogenetics Implementation Consortium guideline for CYP2D6, OPRM1, and COMT genotypes and select opioid therapy. Clin Pharmacol Ther. 2021;110(4):888-896. doi:10.1002/cpt.2149
6. British Columbia Ministry of Health. Pharmacogenomics testing – Information for patients. Updated January 26, 2026. gov.bc.ca
7. Papastergiou J, Quilty LC, Li W, et al. Pharmacogenomics guided versus standard antidepressant treatment in a community pharmacy setting: a randomized controlled trial. Clin Transl Sci. 2021;14(4):1359-1368. doi:10.1111/cts.12986
8. Swen JJ, van der Wouden CH, Manson LE, et al. A 12-gene pharmacogenetic panel to prevent adverse drug reactions: an open-label, multicentre, controlled, cluster-randomised crossover implementation study. Lancet. 2023;401(10374):347-356. doi:10.1016/S0140-6736(22)01841-4