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5 Factors That Can Cause A Decrease In Medication Effectiveness

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Is medication part of your physical or mental health treatment plan? The growing movement focusing on nutritional health has led to heightened concerns of what you put into your body and the impact it has on your overall health and wellness. This should extend to the impact on your medications as well. Certain factors can cause a decrease in medication effectiveness by influencing your metabolism and absorption of medications. Let’s go over the basics of those.

When you take most medications, they pass through your digestive system and your liver. This process is called drug metabolism, and cytochrome P-450s (CYP450s) are the enzymes that do most of the work. These enzymes break down the medication into potentially active or inactive substances called metabolites. Some medications only become active after metabolism, while others lose their impact once they are metabolized. The rate at which your body metabolizes medications can impact a drug’s efficacy.

Below, learn about the five factors that can cause a decrease in medication effectiveness (among other reactions): human error, diet, lifestyle choices, other drugs, and your genetics.

How Human Error Can Cause A Decrease in Medication Effectiveness

The first step to increasing your chances of your medication being effective is taking your medication as prescribed, better known as medication adherence. If you don’t follow the instructions included with your prescription as they relate to dosage, timing, and how to take the drug, you may end up with too much or too little of the drug in your body. This can cause a decrease in medication effectiveness.

For example, some drugs are prescribed to be taken after meals because food can affect their absorption. In addition, birth control must be taken around the same time every day to ensure an appropriate amount of medication is in your system at all times to prevent pregnancy.

While medication adherence falls on you, medication errors can cause a decrease in medication effectiveness, and those may not be your fault. For instance, if your healthcare provider accidentally orders you the wrong dose of a drug, it may cause the drug to not be effective for you. We expand on this topic further in our guide on How to Avoid Medication Errors.

However, the effectiveness of your medication rests on more than just taking it correctly. Your diet, lifestyle, and personal genetics can impact medications more than you may realize.

Foods That Can Interact With Medications

The foods you eat can interact with medication metabolism and absorption, which can enhance or interfere with the effectiveness of the medication. Additionally, these food-drug interactions can potentially increase the chances of having an adverse event (think: side effects) or worsen the impact of that adverse event.


Statins are drugs that lower cholesterol. Some compounds in grapefruit juice can inhibit CYP3A4/5, an enzyme involved in the metabolism of many medications, including statins. If these medications are processed too slowly, there can be an increase in the risk of side effects.

Dairy Products

When dairy products are digested, iron can be swept out of the body instead of being absorbed. Because of this, it is recommended that iron supplements are not be taken within several hours of dairy consumption. The calcium in dairy products can also reduce the absorption of some antibiotics and thyroid medications.

Dietary Vitamin K

Green leafy vegetables like spinach, kale, and Brussels sprouts are rich in vitamin K. This nutrient is vital for normal blood clotting, but it can make the blood thinner coumadin (warfarin) less effective.

Potassium-Rich Foods

Some blood pressure medications may cause increases in potassium levels. Eating potassium-rich foods, such as bananas and potatoes, can further increase potassium. Eating these foods in conjunction with blood pressure medications can lead to elevated potassium levels and may increase the risk for arrhythmias or a dangerously irregular heartbeat. (While this is not a food-drug interaction that can cause a decrease in medication effectiveness, it is an important one to be aware of for its safety implications.)

Lifestyle Choices That Can Influence Medication Effectiveness

Your body may metabolize medications differently when other substances, like caffeine, alcohol, or compounds from tobacco smoke are present. These lifestyle factors can cause a decrease in medication effectiveness and/or influence your tolerability of a medication.


Compounds in tobacco can alter the ways your body metabolizes medications. While nicotine has other harmful effects on your health, most medication interactions come from the smoke itself. Compounds in tobacco smoke can increase an individual’s metabolism rate, making certain medications less effective. In this case, physicians may need to prescribe higher doses of some medications to achieve the desired effect.

Additionally, smoking can increase the risk of cardiovascular problems in people taking certain birth control pills. It may also interact with some medications that treat cancer, Parkinson’s disease, and mental health disorders.

Caffeinated Beverages

Caffeine can affect medications in a variety of ways. Because caffeine is so commonly consumed, it’s vital to understand how your medications may be affected.

Alcoholic Beverages

Alcohol can have varying effects on the CYP450 enzymes responsible for medication metabolism. Additionally, depending on the medication with which it is combined, alcohol poses the dangers of liver damage, palpitations, or even stomach bleeding.

Because of alcohol’s depressant effect, any medications with a similar side effect can be dangerous. You may experience drowsiness, a slowed heart rate, blood pressure changes, difficulty in breathing, and loss of coordination when consuming alcohol and a depressant.

Alcohol may interact with many common medications, including:

  • Over-the-counter medications for cold and flu
  • Medications with caffeine or other stimulants
  • Prescription painkillers
  • Antidepressants
  • Antibiotics

How Genetics Can Cause A Decrease in Medication Effectiveness

When your genotype affects your ability to absorb or process a drug, it is called a drug-gene interaction. These are very common – it’s estimated that more than 90% of people could have a genetic variation that may cause a drug-gene interaction. These drug-gene interactions can cause a decrease in medication effectiveness. How?

Your genetic makeup can affect your response to certain medications.

Many medications achieve their therapeutic effect by attaching to a cell receptor: a protein on the outside of a cell that can accept signals from medications. Genetic variations in pharmacodynamic (PD) genes can change how the receptors or proteins work. When this happens, the medication may be less likely to be effective.

Your genes can impact your metabolism of medications.

As we said earlier, CYP450s do most of the work to metabolize drugs in your body. 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 differently than normal metabolizers. Fast (also referred to as rapid or ultrarapid) metabolism, can lead to lower blood levels of the medication and a decrease in medication effectiveness, while slow (also known as intermediate or poor) metabolism, can lead to an increased risk for side effects.

For instance, variants of the CYP2C19 gene are associated with enhanced activity, which can lead to rapid metabolism and loss of effectiveness for some of the selective-serotonin reuptake inhibitors (SSRIs), common medications used for treating depression and anxiety. Metabolizing SSRIs like citalopram and escitalopram too quickly may lead to subtherapeutic levels of the drug, i.e. a decrease in medication effectiveness.

In this way, looking at your genes can shed light on which medications may be more likely to be effective for you.

How Drug Interactions Can Cause A Decrease in Medication Effectiveness

When two medications interact with each other it is known as a drug-drug interaction.

Just like gene-drug interactions, some drug-drug interactions can increase or decrease the CYP450 enzyme’s metabolic function, i.e. cause the CYP450s to metabolize drug(s) faster or slower, which can impact medication effectiveness and your risk of side effects.

Drug-drug interactions can also impact how a drug acts on its target receptor. One example would be how the opioid receptor antagonist naltrexone can block the pain relieving effects of opioid medications like morphine. In this way, drug-drug interactions can decrease medication effectiveness.

Finding Safe and Appropriate Medication Choices

The lifestyle you live and what you decide to put in your body everyday, in combination with your personal genetic profile, may affect how your body responds to medication(s). So how do you find helpful medication guidance with these considerations in mind?

Enter: Genomind’s Precision Health Platform. Combining pharmacogenetic testing with medication management software and clinical expertise, your clinician can make more personalized prescribing decisions.

Pharmacogenetic testing from Genomind, which is available by prescription, looks at 24 genes related to your metabolism, absorption, and sensitivity to medications. It can help your clinician determine:

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

This testing makes your clinician aware of gene-drug interactions. To account for drug-drug interactions, your diet and lifestyle factors (such as caffeine consumption and smoking), Genomind’s platform uniquely offers GenMedPro™. This precision medicine software uses results from the PGx test to allow your clinician to explore various prescribing options to reduce unintended risks.

Together, these tools can provide your clinician helpful information to make a more informed decision about your medication(s) and dosage.

Bottom Line

Your personal genetic profile, prescriptions, diet, and lifestyle choices are among the factors that can cause a decrease in medication effectiveness. Using Genomind’s services gives you and your clinician helpful insights on what medications may be more likely to be effective for you. This information, along with detailed information on your diet, lifestyle, and other specific factors, can allow for a more individualized approach to your treatment, and increase the likelihood of medication effectiveness.

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