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What Everyone Needs to Know About Drug Metabolism

four pill bottles varying in size smallest to largest

Drug therapy is a common part of everyday life, from managing acute illnesses to treating chronic conditions. Nearly 49 percent of people in the United States used at least one prescription drug in the last 30 days, according to the Centers for Disease Control and Prevention (CDC). And that doesn’t count the over-the-counter medications that people also take.

Understanding how your body metabolizes medications may explain how a certain drug works for reducing your symptoms, or whether you’ll receive any relief from it at all. In some cases, even with the same diagnosis as someone else, your dose of a drug may be higher or lower, or you may need an entirely different medication, to achieve the same relief.

The CDC estimates that each year, some 1.3 million people—or one in 250 Americans—go to the emergency room because of a bad reaction to a medication. More than a quarter of them will need to be hospitalized for additional treatment.

The drug classes most responsible for these adverse drug events are blood thinners, antibiotics, diabetes drugs, and opioid analgesics. In an era of opioid addiction and overdose, as well as a rising number of mental health diagnoses, medication metabolism may be critical to understanding appropriate dosing of opioids and other medications.

What Your Body Does with Drugs

How your body chemically alters pharmaceuticals so that they can be more easily processed and excreted, is called medication metabolism. Watch the video below.

Even though it occurs in many of your body’s tissues, your liver holds the main responsibility for drug metabolism. It contains enzymes that usually break down or inactivate drugs. In some cases, though, these enzymes actually convert the drug into a form that your body can use more effectively. Other proteins, known as p-glycoproteins, can affect the absorption or brain penetration of certain drugs—in particular, some opioids and antidepressants.

The rate at which your body metabolizes medications can impact both the drug’s efficacy and toxicity. It’s one of the main reasons why you can experience success with drug therapy, or get into trouble. For instance:

If your body metabolizes a drug too quickly, you may not get any benefit from the prescribed dose. Your dose may need to be increased to reach a therapeutic effect.

If your body metabolizes a drug too slowly, it stays active longer, and may be associated with side effects.

Because of this, your doctor may characterize you as being one of four metabolizer types, with respect to a specific enzyme.

  • Poor metabolizers have significantly reduced or non-functional enzyme activity.
  • Intermediate metabolizers have low or reduced enzyme activity.
  • Extensive metabolizers have normal enzyme activity.
  • Rapid or ultra-rapid metabolizers have high enzyme activity.

What Determines Your Drug Metabolism?

Several factors affect your body’s rate of metabolism.

Genetic Factors

Of all the metabolic enzymes, the enzymes produced by the cytochrome P450 (CYP450) gene group are among the most important. They make up 70 to 80 percent of enzymes involved in drug metabolism.

However, there are thousands of naturally-occurring genetic variants. If you have a genetic variant or mutation for a CYP450 gene, you may metabolize certain drugs, such as psychiatric medications, differently than normal metabolizers.

Coexisting Disorders

Underlying health conditions can also influence your drug metabolic rate. Some conditions at greater risk of this are chronic liver disorders, kidney dysfunction, or advanced heart failure.

Drug and Food Interactions

The ability of CYP450 enzymes to break down drugs can be impacted by the foods you eat and other drugs you take. When drug-drug interactions increase the enzyme’s metabolic function, the said drug’s therapeutic effects may be decreased. When they decrease the enzyme’s metabolic function, said drug’s benefits may be compromised by intolerability.


Your metabolic enzyme systems change throughout your lifetime. At birth, these systems are only partially developed. That’s why newborns have difficulty metabolizing certain drugs. It’s one of the reasons why pediatric doses are lower than adult doses, and why some medications aren’t safe for infants or children.

Starting in late middle-age, our risk of medication side effects increases, in part because decreased blood flow and liver volume reduce the CYP450 enzyme activity in the liver by 30 percent or more. Because of this, older people can have difficulty metabolizing drugs. Like infants and children, older adults often need smaller doses per pound of body weight, compared to young or middle-aged adults.

The goal for any drug treatment plan is being on the appropriate medication, at the appropriate dose. Knowing your medication metabolism is a key piece of the puzzle that can help you optimize efficacy while reducing or eliminating side effects.

Genetic Testing for Medication Metabolism

Traditional treatment has followed a pattern: a doctor prescribes, you adhere, and either the treatment provides relief or it doesn’t—and, in some cases, you may suffer side effects. However, treatment doesn’t have to be trial and error-based.

For decades, people have been trained to know their blood type. With developments in the field of personalized medicine, more people now understand the importance of knowing their personalized gene information related to drug metabolism as well.

This is further supported by the FDA, which requires over 270 medications to include pharmacogenetic guidance on their manufacturing labels, due to specific actionable gene-drug interactions. Your personalized metabolism profile can be determined through genetic testing.

Pharmacogenetics (PGx) testing identifies if you have variants of pharmacokinetic genes, such as CYP450, that could affect your body’s metabolism of a drug. The insights provided by PGx can help inform dosing decisions. Such tests can also provide information on genes that play a role in determining a drug’s effect on the body, which can help inform drug selection.

Genomind’s pharmacogenetic testing, which is available by prescription, looks at 24 genes related to mental health treatment. It provides guidance across 10+ mental health conditions and 130+ medications to help clinicians determine:

  •       Which medications may be more likely to be effective
  •       Which medications may be more likely to lead to side effects
  •       How you metabolize medications for personalized dosing guidance

With every Genomind pharmacogenetic report, you are provided with your unique individual Patient Metabolism card – which provides a snapshot of your personal metabolism profile. You can share your card with any healthcare provider (not just the provider that ordered the test for you) to help inform prescribing decisions beyond mental health. Your genes do not change, so your results are good for life.

Does Your Medication Work for You?

Genomind’s leading pharmacogenetic test was designed to help your clinician personalize your treatment plan based on your genetic profile. Get started today.

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