Psychiatric Pharmacogenetics
What Is Psychiatric Pharmacogenetics?
Psychiatric pharmacogenetics examines how genetic differences may influence a person’s response to medicines used to treat mental health conditions. By analysing selected genetic variations, pharmacogenetic testing can provide information about how the body processes certain psychiatric medicines and may help inform prescribing decisions in appropriate clinical situations. This is a specialised application of pharmacogenomics, which explores how genetic variation can influence responses to medicines.
Genetic variations in drug-metabolising enzymes, including CYP2D6 and CYP2C19, can affect how quickly some medicines are processed. Depending on the medicine and the genetic findings, this information may help a healthcare professional assess whether a treatment or dosage warrants further review.
Psychiatric pharmacogenetic testing is different from genetic testing designed to investigate the inherited causes or risk of a mental health condition. It does not diagnose conditions such as depression, bipolar disorder or schizophrenia, nor can it determine with certainty which medicine will work best for an individual. Instead, it provides additional information that may support clinical assessment alongside medical history, current medicines and other relevant factors.
How Can Genetic Differences Influence Responses to Psychiatric Medicines?
Genetic variations can influence how the body absorbs, processes and eliminates certain psychiatric medicines. Differences in drug-metabolising enzymes may cause some people to process a medicine more slowly or more quickly than expected, potentially affecting the amount of the drug in the bloodstream and how long it remains in the body. For example, variations in the CYP2D6 and CYP2C19 genes can affect the metabolism of certain antidepressants and other psychiatric medicines. Depending on the specific medicine, slower metabolism may contribute to higher drug exposure and an increased likelihood of dose-related side effects. Faster metabolism may result in lower drug exposure and potentially reduce treatment effectiveness. However, these effects vary by medicine, and faster metabolism does not always mean a medicine will be less effective. Genetic differences do not determine treatment response on their own. Other factors, including the prescribed dose, interactions with other medicines, liver function, age and general health, can also influence drug levels and tolerability. A healthcare professional can interpret pharmacogenetic findings alongside these factors to assess whether treatment or dosage adjustments may be appropriate.Which Genes Are Most Relevant to Psychiatric Pharmacogenetic Testing?
Several genes have been studied for their influence on psychiatric medicine response, but the strength of clinical evidence varies. The genes below illustrate the difference between established gene–medicine guidance and findings that have more limited value for routine prescribing.
| Gene | Role | Examples of clinical relevance | Evidence and clinical use |
|---|---|---|---|
| CYP2D6 | Helps the body metabolise several psychiatric medicines. | Selected antidepressants, including paroxetine and venlafaxine, and certain antipsychotics. | Stronger evidence for specific gene–medicine pairs, with prescribing guidance available for selected medicines. |
| CYP2C19 | Influences the metabolism of several antidepressants. | Citalopram, escitalopram and sertraline. | Stronger evidence for selected antidepressants, including guidance that may inform dose or medicine selection. |
| CYP2B6 | Contributes to the metabolism of certain antidepressants. | Sertraline, for which genotype may contribute to prescribing guidance. | Clinically relevant for selected medicines, but its usefulness depends on the specific drug and applicable guideline. |
| HLA-B and HLA-A | Influence immune recognition rather than drug metabolism. | Certain variants, including HLA-B*15:02 and HLA-A*31:01, are associated with severe skin reactions to carbamazepine. | Important drug-specific safety associations in relevant populations; testing recommendations depend on the medicine and clinical guidance. |
| SLC6A4 and HTR2A | Related to serotonin transport and receptor signalling. | Studied in relation to antidepressant response and tolerability. | Evidence is more limited or inconsistent for guiding routine prescribing; these findings should not be treated as equivalent to established gene–medicine recommendations. |
The clinical importance of a genetic result depends on the specific medicine, the variant identified and the relevant prescribing guideline. Even for genes with stronger evidence, results do not independently determine which treatment will be most effective. A healthcare professional should interpret them alongside symptoms, treatment history, other medicines and individual clinical circumstances.
Which Psychiatric Medicines May Be Affected by Genetic Variation?
Genetic variation can influence how some psychiatric medicines are processed by the body, their potential side effects and, in certain cases, prescribing decisions. The clinical relevance depends on the specific medicine and the strength of evidence supporting its use with pharmacogenetic results.
Antidepressants
Some antidepressants have established pharmacogenetic guidance. For example, genetic variation may inform prescribing decisions for medicines such as citalopram, escitalopram, sertraline, paroxetine and venlafaxine. Understanding the relationship between antidepressants and genetics can provide further context on how genetic factors may influence treatment decisions. Depending on the medicine and the individual’s results, a healthcare professional may consider whether the dose or treatment plan requires review.
Antipsychotics
Pharmacogenetic findings may also be relevant to selected antipsychotics, including aripiprazole and risperidone, particularly when interpreting differences in drug metabolism. However, the availability and strength of prescribing recommendations vary by medicine. Genetic results are only one part of assessing treatment response, tolerability and other clinical considerations.
Mood Stabilisers and Other Psychiatric Medicines
The role of pharmacogenetics differs across mood stabilisers and other medicines used in mental health care. For example, specific HLA genetic variants are associated with an increased risk of serious skin reactions to carbamazepine in relevant populations. This is a drug-specific safety consideration rather than a general prediction of treatment effectiveness.
By contrast, routine genetic testing has limited established value for guiding the use of some other medicines, including lithium. The evidence for using pharmacogenetic results to guide treatment with mood stabilisers is not uniform, so recommendations should be based on the individual medicine and applicable clinical guidance.
Pharmacogenetic testing does not provide a definitive ranking of psychiatric medicines or guarantee a better response. A qualified healthcare professional should interpret any findings alongside symptoms, previous treatment outcomes, current medicines and other relevant clinical factors.
Who May Benefit from Psychiatric Pharmacogenetic Testing?
Psychiatric pharmacogenetic testing may be worth considering when genetic information could help clarify a medicine-related clinical question. Its potential usefulness depends on the medication being considered, the available evidence and the individual’s treatment history. It is not necessary or beneficial for everyone receiving psychiatric medication.
A healthcare professional may consider testing in situations such as:
- Limited response to previous treatment: When symptoms have not improved as expected despite an appropriate treatment trial, pharmacogenetic findings may provide additional information for reviewing selected medicines.
- Previous side effects or poor tolerability: If a person has experienced troublesome adverse effects, relevant genetic findings may help assess whether drug metabolism could be a contributing factor.
- Unusual responses to standard doses: When a medicine appears to have an unexpectedly strong or weak effect, testing may help inform a review of treatment, where established gene–medicine guidance is available.
- Considering a medicine with established pharmacogenetic guidance: Testing may be relevant when a specific genetic result can inform prescribing or safety decisions for the medicine under consideration.
- Complex treatment history: For people who have tried several medicines, a clinician may consider whether pharmacogenetic information could add useful evidence to an overall treatment review.
These circumstances do not automatically mean that testing is required. Before recommending it, a healthcare professional should also consider factors such as the prescribed dose, adherence, interactions with other medicines, physical health and the nature of the previous response. Testing is most useful when the result has a clear, evidence-based role in a clinical decision.
Pharmacogenetic testing cannot guarantee that a future medicine will be effective or free from side effects. Its role is to provide additional information that may support individualised prescribing alongside clinical assessment and shared decision-making.
How Does Psychiatric Pharmacogenetic Testing Work?
Psychiatric pharmacogenetic testing typically involves five steps, from identifying a relevant clinical question to discussing how the findings may inform treatment decisions.
1. Assessing the Clinical Need
A healthcare professional reviews the person's medication history, previous responses and side effects to determine whether testing could provide useful information for a specific prescribing decision.
2. Collecting a Sample
A biological sample, commonly saliva or blood, is collected according to the laboratory's requirements. The sample is used to obtain DNA for analysis.
3. Analysing Selected Genetic Variants
The laboratory examines relevant genetic variants, which may include variants in genes involved in processing particular psychiatric medicines.
4. Interpreting the Results
The findings are assessed to identify relevant gene–medicine associations and any prescribing guidance supported by current clinical evidence.
5. Discussing the Findings
A qualified healthcare professional reviews the report alongside symptoms, treatment history, current medicines and other clinical factors to consider appropriate next steps.
Testing and treatment decisions are separate steps. The laboratory report provides genetic information; it does not automatically select a medicine or determine the correct dose. Any treatment change should be based on clinical assessment, relevant prescribing guidance and the individual's circumstances. Medication should not be stopped or adjusted without advice from the prescribing healthcare professional.
How Are Psychiatric Pharmacogenetic Results Used in Treatment Decisions?
Psychiatric pharmacogenetic results can provide additional information when a healthcare professional is reviewing a person’s medication or considering a treatment change. Where reliable gene–medicine guidance is available, the findings may help inform decisions about medicine selection, dosage or the need for closer monitoring.
Interpreting the report involves more than identifying a genetic variant. A healthcare professional considers how relevant the finding is to the specific medicine and reviews it alongside other factors, including:
- Previous treatment response: Whether earlier medicines provided sufficient symptom improvement or caused troublesome side effects.
- Current medicines and supplements: Other substances may affect drug metabolism or interact with treatment, sometimes changing the way a person’s genetic profile translates into a real-world response.
- Dosage and adherence: The prescribed dose and how consistently the medicine has been taken can influence treatment response.
- Individual clinical factors: Age, physical health, liver function and other relevant circumstances may affect medicine exposure and tolerability.
- Clinical guidelines and evidence: Recommendations differ between medicines, so the report should be interpreted using applicable, up-to-date guidance rather than generalised assumptions.
Depending on the findings and the wider clinical picture, the prescriber may decide to continue the current treatment, review the dose, consider an alternative medicine or arrange additional monitoring. For some medicines, personalised drug dosing based on genetics may help inform dose-related decisions when supported by relevant clinical guidance. A genetic result does not automatically require a treatment change, and it cannot reliably predict an individual’s overall response on its own.
Pharmacogenetic information is therefore best used as one part of shared clinical decision-making. Any change to psychiatric medication should be discussed with the prescribing healthcare professional, taking account of the person’s symptoms, preferences, treatment goals and safety.
What Are the Benefits and Limitations of Psychiatric Pharmacogenetic Testing?
Psychiatric pharmacogenetic testing may provide useful information for selected prescribing decisions, but its clinical value depends on the medicine, the genes analysed and the evidence supporting each gene–medicine association.
| Potential Benefits | Limitations |
|---|---|
|
Supporting prescribing decisions Results may help inform medicine selection or dosage for specific medicines when established clinical guidance is available. |
Evidence varies by medicine Not all gene–medicine associations have sufficient evidence to guide routine prescribing, and recommendations differ across medicines. |
|
Understanding possible metabolic differences Relevant genetic findings may help explain why some people process certain medicines differently. |
Cannot predict the full treatment response Genes are only one influence on effectiveness and side effects. Symptoms, dose, adherence, interactions and other clinical factors also matter. |
|
Adding information after treatment difficulties In selected cases, results may contribute to a review of previous side effects or an unexpected response. |
Benefits are not guaranteed Testing does not guarantee symptom improvement, remission, fewer adverse effects or a shorter treatment-selection process. |
|
Providing information that can remain relevant Many inherited genetic variants remain the same throughout life and may inform decisions about more than one medicine, where relevant guidance exists. |
Panels and reports differ Tests vary in the genes and variants analysed, the medicines covered and how results are interpreted. Commercial reports may also include findings with limited clinical utility. |
Psychiatric pharmacogenetic testing is a decision-support tool, not a replacement for clinical assessment. Its findings should be interpreted alongside medical and treatment history, current medicines, symptoms and relevant prescribing guidance. The decision to test—and any subsequent treatment change—should be based on individual circumstances and discussion with a qualified healthcare professional.
What Should You Consider Before Having Psychiatric Pharmacogenetic Testing?
Before having psychiatric pharmacogenetic testing, it is important to understand what the test can tell you, how the results may be used and whether they are likely to inform a specific treatment decision. The following considerations can help you discuss the options with a qualified healthcare professional.
The Purpose of Testing
Consider whether there is a clear clinical question, such as an unexpected response to a particular medicine or a need to review treatment options. Testing is more useful when the results can inform a decision supported by clinical evidence than when it is undertaken without a specific purpose.
Which Genes and Variants Are Analysed?
Ask which genes and genetic variants the test examines and which psychiatric medicines are covered by its report. Different panels analyse different variants, and a broader panel does not necessarily provide more clinically useful information.
How the Results Will Be Interpreted
Find out who will interpret the report and whether the interpretation follows recognised, up-to-date prescribing guidance. Ask how the findings will be considered alongside your treatment history, current medicines and other clinical factors, and whether follow-up with your prescriber is available.
Costs and What Is Included
Check the total cost and whether it includes sample collection, laboratory analysis, interpretation and a consultation to discuss the findings. You may also wish to ask whether repeat testing or additional support could involve extra charges.
Privacy and Use of Genetic Information
Before providing a sample, review the laboratory’s privacy policy and consent process. Understand how your genetic data and sample will be stored, who may access them, how long they will be retained and whether they could be used for research or shared with third parties. Ask whether you can request deletion of stored data or disposal of the sample, and what limits or legal obligations may apply.
How Results May Affect Your Care
Clarify how the results will be communicated to your healthcare professional and whether they are intended to inform a particular prescribing decision. A report does not automatically determine the right medicine or dose, and any treatment changes should be agreed with the clinician responsible for your care.
Taking time to address these questions can help you decide whether testing is appropriate for your circumstances and understand the practical implications before proceeding.
Frequently Asked Questions About Psychiatric Pharmacogenetics
What is psychiatric pharmacogenetic testing used for?
It examines genetic variations that may influence how the body processes certain psychiatric medicines. The results can help inform prescribing decisions when supported by relevant clinical evidence.
Which psychiatric medicines can pharmacogenetic testing help assess?
Testing may inform decisions about selected antidepressants, including citalopram and escitalopram, and some antipsychotics. Specific genetic variants can also be relevant to the safety of certain medicines, such as carbamazepine. Clinical usefulness varies by medicine.
Can psychiatric pharmacogenetic testing identify the best antidepressant for me?
No. Testing cannot reliably identify a single best medicine or guarantee treatment success. Results provide additional information that must be considered alongside symptoms, medical history and previous treatment responses.
Can the test explain why a psychiatric medicine caused side effects?
In some cases, yes. Genetic differences affecting the metabolism of particular medicines may contribute to drug exposure and side effects. However, adverse effects can have many causes, and genetic testing cannot explain every reaction.
Does psychiatric pharmacogenetic testing diagnose depression or other mental health conditions?
No. It assesses genetic variations relevant to medication response, not whether someone has depression, bipolar disorder, schizophrenia or another psychiatric condition.
Is psychiatric pharmacogenetic testing suitable for everyone taking psychiatric medication?
Not necessarily. It may be worth considering when there is a specific clinical question and reliable guidance exists for the medicine involved. A healthcare professional can help determine whether testing is appropriate.
Does psychiatric pharmacogenetic testing need to be repeated?
Usually, the inherited genetic profile being tested does not change over a person’s lifetime, so the same genetic test generally does not need to be repeated. However, new medicines, updated clinical guidance or changes in health may affect how the existing results are interpreted.
Can genetic results determine the correct dose of psychiatric medication?
Not on their own. For certain medicines, genetic findings may inform dose recommendations, but the final decision also depends on clinical factors such as other medicines, physical health, treatment response and tolerability.
How long does it take to receive psychiatric pharmacogenetic test results?
The turnaround time depends on the laboratory, the test panel and the reporting process. Ask the testing provider for its estimated timeframe and whether clinical interpretation or a follow-up consultation is included.
Should I stop taking my medication before having the test?
No. Do not stop or change prescribed psychiatric medication solely because you are having a genetic test. Discuss any concerns and potential treatment changes with your prescribing healthcare professional.
Discuss Psychiatric Pharmacogenetic Testing with Our Team
If you are considering psychiatric pharmacogenetic testing, London Genetics can help you explore the available options and understand what to consider before proceeding.
Get in touch to discuss your circumstances, the purpose of testing and the most appropriate next steps for your needs.
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