Drug interactions: A guide for consumers

We live in a world where incredible drugs exist to treat many conditions that seemed untouchable in the past.

It’s encouraging to know that there are options to address many of our common ailments. However, the impressive availability of medications also increases the possibility of drug interactions.

What is a drug interaction?

Drug interactions involve combinations of a medication with other substances that alter the medication’s effect on the body. This can cause the medication to be less or more potent than intended or result in unexpected side effects.

If you use multiple medications, have certain health conditions, or see more than one doctor, you should be especially mindful of your medications. You also need to make sure that each of your doctors know all of the drugs, herbs, supplements, and vitamins you’re using.

Even if you take only one medication, it’s a good idea to talk with your doctor or pharmacist about what you’re using to identify possible interactions. This advice applies to both prescription and nonprescription drugs.

Types of drug interactions

There are several different types of drug interactions to be aware of. Let’s explore each one a little further.

  • Drug – Drug

A drug-drug reaction is when there’s an interaction between two or more prescription drugs.

One example is the interaction between warfarin, an anticoagulant (blood thinner), and fluconazole, an antifungal medication. Taking these two drugs together can lead to a potentially dangerous increase in bleeding.

  • Drug – Nonprescription treatment

This is a reaction between a drug and a nonprescription treatment. These include over-the-counter (OTC) medications, herbs, vitamins, or supplements.

An example of this type of interaction can occur between a diuretic –a drug that attempts to rid the body of excess water and salt –and ibuprofen. The ibuprofen may reduce the diuretic’s effectiveness because ibuprofen often causes the body to retain salt and fluid.

  • Drug – Food

This happens when food or beverage intake alters a drug’s effect.

For example, some statins (used to treat high cholesterol) can interact with grapefruit juice. If a person who takes one of these statins drinks a lot of grapefruit juice, too much of the drug may stay in their body, increasing their risk for liver damage or kidney failure.

Another potential outcome of the statin-grapefruit juice interaction is rhabdomyolysis. This is when skeletal muscle breaks down, releasing a protein called myoglobin into the blood. Myoglobin can go on to damage the kidneys.

  • Drug – Alcohol

Certain medications shouldn’t be taken with alcohol. Often, combining these drugs with alcohol can cause tiredness and delayed reactions. It can also increase your risk for negative side effects.

  • Drug – Disease

This interaction is when the use of a drug alters or worsens a condition or disease. Additionally, some medical conditions can increase the risk of side effects from specific drugs.

For example, some decongestants that people take for colds can increase blood pressure. This is a potentially dangerous interaction for people with high blood pressure (hypertension).

Another example is metformin (a diabetes drug) and kidney disease. People with kidney disease should use a lower dosage of metformin or not take it at all. This is because metformin can accumulate in the kidneys of people with this disease, increasing the risk of severe side effects.

  • Drug – Laboratory

Some medications can interfere with specific laboratory tests. This can result in inaccurate test results.

For instance, tricyclic antidepressants have been shown to interfere with skin prick tests used to determine whether someone has certain allergies.

Other factors in drug interactions

While it’s important to educate yourself on your potential for drug interactions, understand that this information doesn’t tell you everything you need to know. Just because a drug interaction can occur doesn’t mean it will.

Personal traits can play a role in whether a drug interaction will happen and if it will be harmful. Specifics about your drugs, including dosage, formulation, and how you take them, can also make a difference.

The following factors of an individual’s medical history influence possible drug interactions:

  • Genetics

Variations in individual genetic makeup can make the same drug work differently in different bodies.

As a result of their particular genetic code, some people process certain medications more quickly or more slowly than others.

This may cause the drug levels to go down or go up more than expected. Your doctor will know which drugs require genetic testing to find the correct dosage for you.

  • Weight

Some drugs are dosed according to how much a person weighs.

Weight changes could affect dosage and also increase or decrease the risk of drug interactions. So if you have a substantial change in your weight, you could need a different dosage of some medications.

  • Age

As we age, our bodies change in many ways, some of which may affect how we respond to medications. The kidneys, liver, and circulation system may slow down with age. This can slow the breakdown and removal of drugs from our bodies.

  • Sex (male or female)

Differences between the sexes, such as anatomy and hormones, can play a part in drug interactions.

For example, the recommended dose of zolpidem (Ambien) given to women was lowered to half the amount prescribed to men. This happened after research found that women were more likely to have high levels of the drug in their system in the morning, when it could impair activities like driving.

  • Lifestyle (diet and exercise)

Certain diets can be problematic when combined with medication.

For example, research has shown that high fat intake can reduce the response of bronchodilators, which people with asthma use to treat symptoms.

Exercise can also change how medications work.

For example, people who use insulin to treat diabetes can experience hypoglycemia (low blood sugar) during exercise. So they may need to adjust the time they eat and take their insulin to offset the drop in blood sugar.

Smoking cigarettes can also affect the metabolism of some drugs. Be sure to mention to your doctor that you smoke if they’re recommending you start a new medication.

  • How long the drug is in your body

Many factors affect the speed at which the body absorbs and processes drugs. The right dose for each person may depend on such factors, and may be higher or lower than the typical dose. This is another reason why your doctor needs to know all the drugs you’re taking before prescribing a new medication.

  • How long you’ve been taking the drug

The body can become tolerant to some medications, or the drugs themselves may help the body to process them more quickly over time. So dosages may have to be adjusted if they are taken for a long time. Two examples are pain drugs and antiseizure drugs.

  • Dose

The term “dose” is the amount of medication prescribed to be taken or administered. (You may sometimes hear the term “dosage,” which refers to an amount of medication given at specific periods of time — for example, once a day.)

Two people taking the exact same drug may be prescribed different doses. Calculating the proper dose requires precision, so you shouldn’t alter how much of a medication you take without consulting with your doctor first.

  • How the drug is taken or administered

There are many different ways a drug can be administered. Some common ways we take drugs include orally (by mouth), by injection, and topically (applied to the skin). The way medications enter the body can greatly alter the resulting effects.

  • Formulation

The formulation of a medication is the specific mixture of ingredients the drug contains. A medication’s formulation is important because it can determine, in part, how the drug acts in the body as well as its effectiveness.

  • The order in which medications are taken

Some drug interactions can be reduced or eliminated if the drugs are taken at different times.

Certain drugs may affect the absorption of other drugs when taken one before the other. Antacids like calcium tablets can prevent the absorption of the antifungal medication ketoconazole, for example.

Source: Health Line


Stellapharm is one of leading generics pharmaceutical companies and strong producer of anti-viral drugs in Vietnam. The company established in Vietnam in 2000; and focuses on both prescription drugs and non-prescription especially in cardiovascular diseases, antiviral drugs, anti-diabetics drugs, etc. and our products are now used by millions of patients in more than 50 countries worldwide.

The company is globally recognized for its quality through our facilities have been audited and approved by stringent authority like EMA, PMDA, Taiwan GMP, local WHO and others.

Additional information for this article: Stellapharm J.V. Co., Ltd. – Branch 1
A: 40 Tu Do Avenue, Vietnam – Singapore Industrial Park, An Phu Ward, Thuan An City, Binh Duong Province, Vietnam
T: +84 274 376 7470 | F: +84 274 376 7469 | E: info@stellapharm.com | W: www.stellapharm.com

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