A Note on Genetic Testing and Antidepressants

Have you ever taken medication and experienced no change in your symptoms? Or, perhaps taking certain medication has made your symptoms worse? Maybe you’ve experienced the human guinea pig phenomenon, experimenting with different meds in the hope of finding something (anything!) that works. If this sounds familiar, you are certainly not alone.

Factors that affect how we react to drug medication

There are several factors that influence how we will respond to medication:

  • Age

  • Gender

  • Ethnicity

  • Symptom profile

  • Drug v drug interactions

In addition, we know now that genetics play a significant role in the success (or failure) of medication.

With specific reference to psychiatric medication such as SSRI’s, two enzymes are particularly important:

1. CYP2D6

2. CYP2C19

These enzymes are needed to metabolize medication and influence what our body does when certain drugs enter our system (pharmacokinetics) as well as what the drugs do to the body (pharmacodynamics).

Importantly, these enzymes vary between individuals. The result is that some people can metabolize drugs rapidly (ultra metabolizers) whereas others may have a reduced ability to do so. In fact, around 1 in 20 people (5%) in the UK are ‘poor’ metabolizers. In Asia, this number is higher at around 1 in 6 people (17%).

Metabolic status is critical

This information is critical, because if a drug is metabolized too slowly, it may result in toxicity. Drug toxicity occurs when a person has accumulated too much of a drug in the bloodstream, leading to adverse effects on the body. You can read more about the signs and symptoms of toxicity here.

Therefore, it makes sense that a poor metabolizer should be prescribed a lower dosage to prevent a negative reaction.

Similarly, if a drug is metabolized too quickly, it will decrease its success.

In the case of antidepressants and anti-psychotics, drug efficacy may be the difference between life and death.

This begs the question: should genetic testing be carried out before antidepressant and anti-psychotic medication is prescribed, to determine how individuals are likely to respond?