The Most Common Drug Interactions

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The Most Common Drug Interactions

Written by Equipo Editorial

Last update: 24 March, 2023

When a patient takes a drug, its effect on the body may be different than expected due to the different types of possible drug interactions. For this reason, it’s essential not to self-medicate and to be under medical supervision when you are under treatment.

The effects of drug interactions are often unwanted and sometimes harmful. In addition, drug interactions can intensify or reduce the action of one or more drugs leading to side effects or treatment failure.

On the other hand, we can distinguish two types of drug interactions:

  • Pharmacodynamics: When the interaction affects the pharmacological actions triggered by the drug in the body.
  • Pharmacokinetics: When what is altered are the processes of absorption, distribution, metabolism, and excretion of the active principle.

The most common interactions that we will see below are:

  • Drug interaction
  • Drug and nutrient interactions
  • Drug-disease interaction

Drug interaction

Drug interactions can occur with both prescription and over-the-counter drugs.

It is the obligation of both the doctor and the pharmacist to explain to the patient the possible interactions that the drugs they are prescribing them may have.

Drug interactions.

Effects that can appear with these types of interactions include duplication and antagonism. These drug interactions are pharmacodynamic.


This effect derived from drug interaction occurs when drugs have the same effect. The adverse reactions of both can be intensified.

For example, you could take a cold medicine and a pain reliever at the same time, both with acetaminophen. The probability of this type of effect is high with the use of drugs that contain multiple ingredients or that are sold under brand names; they seem different, but their composition is the same.


This effect occurs with two drugs with opposite actions. In this way, the effectiveness of one or both can be reduced.

An example here is the case of the joint administration of an NSAID such as ibuprofen together with a diuretic such as hydrochlorothiazide.

NSAIDs, which are administered to relieve pain, can cause salt and fluid retention in the body. On the other hand, the diuretic helps to eliminate excess salt and fluids from the body. Consequently, if a person takes both types of drugs, the first can reduce the effects of the second.

Drug and nutrient interactions

Food, drinks and dietary supplements are considered nutrients. The use of substances of this type can alter the effects of the medication being taken.


Drugs taken orally must be absorbed through the wall of the stomach and small intestine. Consequently, the presence of food in the digestive tract can reduce the absorption of a drug. To prevent this interaction, the medicine is usually taken 1 hour before or 2 hours after a meal.


Alcohol and pills.

Although alcohol isn’t a nutrient in itself, it acts on organic processes and interacts with many drugs. For example, drinking alcohol with an antibiotic such as metronidazole can cause a number of undesirable adverse reactions.

Dietary supplements

These are products that contain vitamins, minerals, herbs or amino acids that are administered with the aim of providing a supplement to the normal diet. They are regulated as food, not as drugs, so they haven’t undergone drug-specific testing.

They can interact with both over-the-counter and prescription drugs. To avoid this potential problem, people taking dietary supplements should tell their doctor and pharmacist.

You may be interested in: When to Take Vitamin Supplements?

Drug and disease interactions

In general, drugs are effective against one disease or illness and are harmful in other disorders. An example of these is the case of some β-blockers given to treat heart disease or high blood pressure that can make asthma worse. Also, in people with diabetes, it makes it difficult to determine low blood sugar levels.

Some medicines used for the common cold make glaucoma worse. Therefore, to avoid complications, the patient must inform the doctor of all the conditions they have before they can prescribe new medication.

Especially significant diseases are:

  • Girona Brumós, L. (2013). Interacciones Farmacológicas: Descripción Y Mecanismos Actitud Clínica Ante Las Interacciones Farmacológicas. Introducción a Las Interacciones Farmacológicas 1a Edición.
  • de Cos, M. A. (1997). Interacciones de fármacos y sus implicaciones clínicas. J. Flores Farmacología Humana.
  • Morales-Olivas, F. J., & Estañ, L. (2005). Interacciones farmacológicas de los fármacos antihipertensivos. Medicina Clinica.
  • Serrano López De Las Hazas, J. I. (2011). Interacciones farmacológicas de los nuevos antirretrovirales. Farmacia Hospitalaria.
  • Girona, L. (2013). Interacciones farmacol??gicas. Pharmaceutical Care Espana.

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