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Drug interactions and adverse side effects are a leading cause of deaths in the US. These drug interactions often involve drugs prescribed for chronic diseases as well as over-the-counter medications and dietary supplements.

Many people, including children and most especially the elderly, are taking more than one drug or supplement on a daily basis. Healthy individuals sometimes take different over-the-counter diet supplements, herbal products, energy drinks containing various chemicals, birth control pills, pain medications as needed, topical creams and ointments, and others. Patients with chronic conditions often receive prescriptions for various drugs, including supplements to boost health, and more. Most of us are not aware that we are perhaps using more than one chemically active substance that may react with other substances, including food and drinks, that may be harmful to our health. Although some reactions are not harmful, some substances may reduce or cancel the effect of another, which may or may not be a disadvantage.

Most doctors warn us about the side effects of drugs and how they may interact with each other. However, some of us do not inform our doctors about every over-the-counter (OTC) medication or supplement we are taking, which may interact with prescription drugs. Most of us also presume that OTC medications are probably safe, since one does not need a prescription to buy them. And when unexpected symptoms take place and we consult the doctor, we sometimes omit information, such as that of taking self-prescribed medications.

It is common for patients with chronic disease to receive prescriptions for more than one drug at a time. Studies show that the rate of adverse drug reactions increases exponentially when patients take at least four medications daily.

It has also been shown that adverse drug reactions are the fourth leading cause of deaths in the US, with more people dying from these compared to AIDS, diabetes or automobile accidents.

Common Types of Drug Interactions

There are various ways by which drugs can interact:

  • Some drugs enhance/increase the effects of another drug. For example, taking a sedative with an antihistamine (for allergies) can cause excessive drowsiness. Fluconazole (an antifungal agent) increases the blood levels of warfarin (an anti-clotting drug), which can result in increased tendency for internal bleeding.

  • Some drugs reduce the effects of another drug. For example, calcium supplements decrease the absorption of some antibiotics like tetracycline if they are taken together. Antacids and oral iron supplements also reduce the absorption of antibiotics like azithromycin and tetracycline in the gastrointestinal tract. St. John's wort, a popularly used herbal product, reduces the therapeutic effects of some drugs, including digoxin, a heart medication, and Cyclosporine, an immunosuppressant, by increasing their breakdown.

  • Combining some medications can cause bizarre side effects. For example, an antidepressant combined with a prescription pain reliever can lead to delirium, euphoria, and restlessness.

  • Taking some drugs with certain foods or beverages such as alcohol can cause side effects like excessive drowsiness and heart irregularities. Spinach and broccoli may reduce the effects of warfarin, while grapefruit juice increases the effects of other drugs, including felodipine (for high blood pressure). Taking some antibiotics with milk products can reduce their absorption, thus reducing their therapeutic effects. People who smoke may need to take higher dosages of certain drugs (such as theophylline), since it increases the latter's clearance from the blood, making it less effective.

Drugs Interacting with Disease

Drugs can interact with a medical condition, such as high blood pressure, to make it worse or produce other side effects. Examples of common medications that can increase blood pressure readings are nasal decongestants and anti-allergy drugs that contain phenylephrine, which can tighten blood vessels. In people who have advanced liver disease or kidney disease, drug metabolism and excretion may be decreased, which may lead to exaggerated drug effects and toxicity. Therefore, a relatively safe drug such as acetaminophen can cause toxic effects in a person who has liver cirrhosis.

Continue reading after recommendations

  • Oregon State University. "One in five older Americans take medications that work against each other." ScienceDaily. ScienceDaily.
  • FDA. Drug Interactions: What You Should Know.
  • AAFP. Clinically Significant Drug Interactions.
  • FDA. Preventable Adverse Drug Reactions: A Focus on Drug Interactions.
  • Photo courtesy of forwardcom by FreeImages :
  • Photo courtesy of pepedelaolla de la olla by Public Domain Pictures :

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