Why do mental health meds affect people differently?

This article was authored in partnership with Prairie Health.

Mental health medication can work well for some people, yet not work at all for others. 40% of psychiatry patients discontinue their medication within 90 days of prescription because of side effects or lack of response [1]. It is increasingly clear that medication does not work the same way for everyone.

There is always some trial and error involved in finding the right medication for you. As of now, there’s no magic formula that will take information about you and predict exactly what medications and dosages will work well for you. Still, understanding why medications affect people differently can help the process feel less mysterious.

Let’s take a look at some of the factors:


When you take medication, your liver breaks down the molecules of the medication over time. Your body does this using proteins called enzymes, and your genes carry the information necessary to make these enzymes and to determine how they function.

Your genes dictate what version of each enzyme your body produces. Different forms of enzymes in the liver can cause your body to process a given medication faster or slower than average. If your enzymes metabolize a medication too quickly, then the medication may not stay in your system long enough for it to work properly. On the other hand, if your enzymes metabolize a medication too slowly, the medication may accumulate in your body—which can lead to negative side effects.

Many healthcare providers have started to use genetic testing to inform treatment decisions. These tests offer information on how your genes differ from others, which will allow your healthcare provider to better determine which medication works best for you.


Older populations are often underrepresented in depression studies, meaning that we have a limited understanding of the different ways in which antidepressant medication can impact the elderly. This is challenging because older adults are especially vulnerable to side effects.

Older adults are more likely to have concurrent medical conditions, such as diabetes and cardiovascular disease. With these concurrent conditions come additional medication. In addition, older adults tend to be slower at metabolizing drugs. Accordingly, if dosages are not adjusted, age can translate to increased side effects [2]. 

Drug Interactions

Drugs often interact with each other [3]. This includes medications for mental and physical health, as well as recreational drugs and dietary supplements. These substances can cancel each other out, amplify each other’s effects (including side effects), or cause other serious problems. When you start a new medication, it’s important to tell your doctor what other medications or other substances you are taking so that the doctor can check for interactions.

Biological sex

Biological sex can help predict your body’s response to mental health treatment. Studies suggest that hormones, metabolism, and body composition can change the way that your body interacts with medications [4].

Factors we know less about

In some cases, there isn’t much available information on how effective medications are for different groups of people. Most antidepressants in use today were developed before the NIH Revitalization Act in 1993 [5], which mandated that women and people of color be included in clinical trials. Before that, most clinical trials were conducted mostly on white men. That means that standard starting dosages for these medications are often less appropriate for other groups.

More than 20 years later, the number of nonwhite patients enrolled in clinical trials is still low [6]. For transgender and gender-nonconforming folks, that number is even lower [7]. That means that when healthcare providers prescribe medication, they are working with incomplete information about how a given medication might work for a specific individual. Many people prefer to see healthcare providers who share their racial or gender identity, since these providers may be more aware of this problem.

What’s next?

So what should you do? Consult your care team! Whether that’s your psychiatrist, your physician or your therapist—effective communication is incredibly important when it comes to medication. Finding someone who specializes in treating people similar to you can be helpful; so can genetic testing.


  1. Abdullah-Koolmees et al. (2015). Medication Discontinuation in Patients After Discharge From a Psychiatric Hospital. The Annals of Pharmacotherapy 49(10), pp. 1085-95. Retrieved from https://doi.org/10.1177/1060028015593763
  2. Wiese. (2011). Geriatric depression: The use of antidepressants in the elderly. BC Medical Journal 53(47), pp. 341-347. Retrieved from https://bcmj.org/articles/geriatric-depression-use-antidepressants-elderly
  3. U.S. Food and Drug Administration. (2013). Drug Interactions: What You Should Know. Retrieved from https://www.fda.gov/drugs/resources-you-drugs/drug-interactions-what-you-should-know
  4. Jacobson. (2014). Psychotropic Drugs Affect Men and Women Differently. Scientific American: Mind. Retrieved from https://www.scientificamerican.com/article/psychotropic-drugs-affect-men-and-women-differently/
  5. National Institutes of Health, U.S. Department of Health & Human Services. (2001). NIH Policy and Guidelines on The Inclusion of Women and Minorities as Subjects in Clinical Research. Retrieved from https://grants.nih.gov/policy/inclusion/women-and-minorities/guidelines.htm
  6. Yates et al. (2020). Representation in Clinical Trials: A Review on Reaching Underrepresented Populations in Research. Clinical Researcher 34(7). Retrieved from https://acrpnet.org/2020/08/10/representation-in-clinical-trials-a-review-on-reaching-underrepresented-populations-in-research/
  7. Owen-Smith et al. (2016). Perceptions of Barriers to and Facilitators of Participation in Health Research Among Transgender People. Transgender Health 1(1) pp. 187-196. Retrieved from http://doi.org/10.1089/trgh.2016.0023

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