Updated October 25, 2021.

Finding the right treatment for depression is not easy. Physicians have many mental health medications from which to choose. However, as we know, only a fraction of patients will respond to any given drug. Thus, physicians often resort to a ‘trial and error’ approach – trying the patient on a medication for a few weeks before moving on to another one until appropriate treatment is found. Unfortunately, as clinical trials such as STAR*D have shown, as many as 70% of patients do not respond to their initial prescribed medication. While the trial and error approach ultimately treats depression in many cases, the lengthy process can prolong suffering and frustration for the patient. Precision medicine, using pharmacogenetic testing, can streamline the process of finding the right treatment for each patient’s depression and result in better outcomes.

The risks of the ‘trial and error’ approach

Delays in finding effective treatment for depression are believed to lead to nonadherence in an estimated 30-60% of patients. Furthermore, adverse drug reactions (side effects) are the leading cause of death in the US. Those linked to antidepressants may lead to psychiatric imbalance, contributing to increased risk of suicide, anxiety and manic behaviours. Other common side effects of treatment for depression include dry mouth, constipation, blurred vision, nausea, tremors, insomnia and cardiac disturbance. These adverse reactions stem from the fact that different individuals respond differently to medications, and much of these differences can be attributed to our unique genetic backgrounds.

How genetic testing can improve the treatment for depression

Pharmacogenetics assesses a person’s ability to metabolize specific medications. Pharmacogenetic testing prior to taking medications can help improve prescription accuracy by determining whether an individual will metabolize a particular medicine and guide the starting dosage. Precision medicine for depression significantly reduces trial and error time and improves treatment outcomes. Pharmacogenetic testing also improves drug safety and reduces the risk of adverse drug reactions since a patient is not exposed to unnecessary medications at potentially harmful doses. The International Society of Psychiatric Genetics (ISPG) recommends promoting educational programs to improve knowledge of genetic medicine among physicians and mental health professionals.

The CAMH center in Toronto completed a large-scale study that demonstrated the value of pharmacogenetics-based medication management for depression – patients on a “mismatched” drug significantly improved when switched to an antidepressant better suited to a person’s DNA. A randomized clinical trial conducted in Canadian pharmacies using Pillcheck proven that PGx-based medication management accelerated patient recovery.

Despite positive clinical studies, including the ICANPIC study, Canada lags behind the US in utilizing pharmacogenetic testing in routine care. Provincial health plans still do not cover these tests, but increasing public awareness and pressure are likely to change this.

Expanding Pharmacogenetic Guidelines

Pharmacogenetic testing with standardized reporting is now recognized as one of the clinical tools that can assist clinicians in selecting optimal therapy. The Clinical Pharmacogenetics Implementation Consortium (CPIC) provides guidelines for implementing pharmacogenetics in clinical settings and has made recommendations on genetic testing for multiple disorders. In addition, FDA has pharmacogenetic labelling for over 260 different medications. Both CPIC and ISPG guidelines highlight genetic variations in the CYP2D6 and CYP2C19 enzymes lead to differences in the metabolism of numerous medications relevant to psychiatry, in particular antidepressants and antipsychotics. Yet, the use of psychiatry-specific pharmacogenetic tests that rely on yet unproven genetic markers is discouraged.

Growing Insurance Coverage for PGx

In North America, the benefits of pharmacogenetic testing are being recognized, and its application is gaining steam. In the US and Canada, many insurance providers cover the cost of pharmacogenetic testing as part of extended workplace health benefits. However, different reimbursement policies and lack of provincial reimbursement greatly influence the adoption of pharmacogenetic tests into clinical practice.

Most insurance companies in Canada offer pharmacogenetic testing, such as Pillcheck, as part of disability management programs. A growing number of large insurers also provide coverage for PGx testing as a part of extended health benefit plans when prescribed by a physician. Pillcheck is also eligible for Health Spending Account reimbursement.

Where to find genetic testing for treatment of depression in Canada

Pillcheck is available for purchase online by consumers. It can also be offered directly to patients through clinics and pharmacies. Learn more here.

Use Pillcheck to get on the right medications and feel better sooner.

Rated 4.6/5 stars on dnatestingchoice.com

Pillcheck is an eligible medical expense for income tax deduction and may be reimbursed through your private insurance or company benefits plan.

References

Bousman CA at al., Review and Consensus on Pharmacogenomic Testing in Psychiatry. Pharmacopsychiatry. 2021 Jan;54(1):5-17.

Eap CB, Tools for optimising pharmacotherapy in psychiatry (therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests): focus on antidepressants. World J Biol Psychiatry. 2021 Oct;22(8):561-628.

Herbild, L., et al., Do guidelines recommending pharmacogenetic testing of psychiatric patients affect treatment costs and the use of healthcare services? Scand J Public Health, 2011. 39(2): p. 147-55.

Ventola, C.L., Pharmacogenomics in clinical practice: reality and expectations. P T, 2011. 36(7): p. 412-50.

Maruf AA et al., Pharmacogenetic Testing Options Relevant to Psychiatry in Canada. Can J Psychiatry. 2020 Feb 1