Reviewed by Alison Wong, RPH.

Updated August 2021.

Post-Traumatic Stress Disorder (PTSD) is a mental health condition characterized by nightmares and flashbacks of past traumatic events, avoidance of reminders of trauma, hypervigilance and sleep disturbance. PTSD is often associated with other psychiatric illnesses such as severe anxiety and depression and may be accompanied by psychotic episodes. PTSD can afflict not only violent crime victims, combat veterans, and first responders but also people working in other high-stress occupations such as hospital nurses and journalists. Almost 40 percent of private security operatives show symptoms of PTSD. Individuals living with PTSD often resort to drugs and alcohol, leading to substance abuse and worsening of psychosis. PTSD is treated by both medications and psychosocial interventions. Pharmacogenetics is an effective tool for selecting appropriate medications and improving treatment for PTSD.

Medication and Psychotherapy for PTSD

Psychotherapy, with or without the use of medication, is considered to be the first-line treatment of PTSD. To support psychological counseling, medication management can also be used to better control anxiety, depression, sleep, drug and alcohol cravings. Successful treatment of PTSD depends on patients’ response and adherence to treatment and engagement through cognitive behavioural therapy (CBT). All medications have side effects but may be particularly severe in people with inherently reduced drug metabolism. Accumulation of a drug in the blood may lead to side effects, thereby decreasing treatment adherence. On the other extreme, when a medication is cleared too fast, it may not improve symptoms and increases the risk of treatment failure. In this summary, we will highlight how the genetics of PTSD patients can impact drug response.

Types of medications for PTSD

Antidepressants

Meta-analyses of medications used to manage PTSD-related symptoms indicate effective pharmacotherapies, including selective serotonin reuptake inhibitors (SSRIs) such as paroxetine, sertraline, fluoxetine, and other agents. For PTSD-related symptoms, SSRIs are considered the first line of treatment. It is important to note that up to 25% of people in Canada may have reduced response to sertraline because of an inherently enhanced clearance by CYP2C19. For patients who are rapid or ultrarapid CYP2C19 metabolizers, the Clinical Pharmacogenetics Consortium guideline recommends initiating therapy at the recommended starting dose and to consider alternative medication not metabolized by CYP2C19 if the patient does not respond to the recommended maintenance dose. Up to 10% of people are poor CYP2C19 metabolizers and may not tolerate sertraline which may lead to a change in medication to paroxetine or fluoxetine. On the other hand, both paroxetine and fluoxetine are metabolized by the CYP2D6 enzyme, which is also subject to a lot of variability between individuals. The Clinical Pharmacogenetics Implementation guidelines can therefore help select an appropriate SSRI according to the patient’s inherited drug metabolism (pharmacogenetics). A randomized controlled trial showed that people suffering from depression and anxiety recovered faster when their medications were optimized using Pillcheck pharmacogenetics testing.

Antipsychotics

If a PTSD patient with psychosis does not respond to SSRIs, then an antipsychotic such as risperidone, quetiapine or olanzapine could be added. The CYP2D6 enzyme metabolizes risperidone. Patients with enhanced CYP2D6 activity may have an inadequate response, while poor metabolizers may experience significant side effects.

Quetiapine is mainly metabolized by the CYP3A4/5 enzymes. Notably, >85% of Caucasians are poor CYP3A5 metabolizers, sometimes called CYP3A5 “non-expressors,” and are considered normal. However, most people of African origin express a functional CYP3A5, resulting in reduced quetiapine concentration in the blood. Thus, for the ethnically diverse North American population, knowing a patient’s pharmacogenetic profile can provide insights into which antipsychotic medications would be more effective and well-tolerated by the patient.

Olanzapine is metabolized mainly by the CYP1A2 enzyme, one of the most “inducible” cytochrome enzymes. CYP1A2 activity is significantly induced in smokers. Therefore, response to olanzapine is reduced in PTSD patients who smoke.

For treatment of sleep disruption and nightmares, prazosin has been found to be efficacious. In addition, prazosin is metabolized by demethylation and conjugation and is, therefore, less susceptible to have altered response in patients with a different pharmacogenetic profile.

Cannabinoids

Research is currently underway to evaluate the potential use of cannabinoids to treat PTSD-associated sleep disruption and nightmares, amongst other symptoms. Although the use of cannabinoids in PTSD patients may worsen psychosis, it may help to reduce anxiety and improve sleep. Cannabinoids currently being evaluated include cannabis for medical purposes, tetrahydrocannabinol (THC) and nabilone. Nabilone is a synthetic cannabinoid similar to delta9-THC and was originally approved for managing nausea symptoms. Nabilone is metabolized by numerous enzymes, including CYP2C9 and CYP3A4. Therefore, patients with reduced CYP2C9 or CYP3A4 activity may have higher exposure, and as a result, could be at higher risk of nabilone-related side effects.

Summary

Pharmacogenetic testing such as Pillcheck can provide critical insights on a person’s metabolic drug profile and guide therapy choices for patients with PTSD and PTSD-associated symptoms.

Selected References

Watts BV, Schnurr PP, Mayo L, Young-Xu Y, Weeks WB, Friedman MJ. Meta-analysis of the efficacy of treatments for posttraumatic stress disorder. J Clin Psychiatry. 2013 Jun;74(6):e541-50.

Zhou Y, Ingelman‐Sundberg M, Lauschke VM. Worldwide Distribution of Cytochrome P450 Alleles: A Meta‐analysis of Population‐scale Sequencing Projects. Clin Pharmacol Ther. 2017 Oct; 102(4): 688–700.

Hicks, JK at al., Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2D6 and CYP2C19 Genotypes and Dosing of Selective Serotonin Reuptake Inhibitors Clin Pharmacol Ther. 2015 Aug; 98(2): 127–134.

Gueorguieva, I, Jackson, K, Wrighten, S.A, Sinha, V.P, & Chien, J.Y Desipramine, substrate for CYP2D6 activity: population pharmacokinetic model and design elements of drug–drug interaction trials Br J Clin Pharmacol. 2010 Oct; 70(4): 523–536.

Pietrzak, R. H., Goldstein, R. B., Southwick, S. M., & Grant, B. F. (2011). Prevalence and Axis I comorbidity of full and partial posttraumatic stress disorder in the United States: results from Wave 2 of the National Epidemiologic Survey on Alcohol and Related Conditions. Journal of anxiety disorders, 25(3), 456-465.

Campbell, D. G., Felker, B. L., Liu, C. F., Yano, E. M., Kirchner, J. E., Chan, D., … & Chaney, E. F. (2007). Prevalence of depression–PTSD comorbidity: Implications for clinical practice guidelines and primary care-based interventions. Journal of general internal medicine, 22(6), 711-718.

Lindley, S. E., Carlson, E., & Sheikh, J. (2000). Psychotic symptoms in posttraumatic stress disorder. CNS spectrums, 5(9), 52-57.