Dangerous Drug Interactions

How many times have you actually read the inserts that come with over-the-counter medications or prescriptions from your doctor? Don’t be ashamed to admit the answer is “never.” That’s very typical. The inserts are not only difficult to read because of the tiny type size, they also contain just enough scientific jargon to make them challenging to understand.

In an ideal world, your health-care professional would give you a patient-friendly recap of the information contained in the insert. Instead, most people are lucky if a pharmacist puts a brightly colored sticker on the medication with words of warning, like “Take with Food.”

You may be wondering, so what? You’ve been taking medications on and off your whole life, and you’re still here. Why start reading drug inserts now? Here’s why: As the number of chronic health problems grows, more people are mixing prescription medications with one another and with over-the-counter drugs in combinations that have never been tested for safety. In addition, drug interactions with food, beverages, and nutritional supplements add a whole new layer of potential complications.

I don’t want to frighten anyone, but I do want to make you aware of the situation. Being informed is the best way to avoid these possibly risky combinations. Or you can learn about these interactions the hard way, like my patient Ned did, although I do hope you take steps to avoid that.

Avoiding Drug Interactions

In my earlier newsletter on conditions that mimic Alzheimer’s disease, I suggested making a list of all your medications and nutritional supplements and keeping it in your purse or wallet. If you haven’t done that yet, please do it now so the list is at hand in case of emergencies or visits to the doctor or pharmacy. Many people see more than one physician and use more than one pharmacy, so it’s important to be able to share this information with each one.

While it’s impossible to detail every potential drug interaction, I can tell you that problems occur in four general areas:

  • Mixing drugs with alcohol
  • Mixing drugs with food
  • Mixing drugs with nutritional supplements
  • Mixing drugs with other drugs

Because of space limitations, here’s a brief overview of these better-known problem areas. This is only the tip of the iceberg. To be on the safe side, please consult your physician or pharmacist if you are wondering about drug interactions.

Drugs and Alcohol

Many people are aware that mixing alcohol with sedatives is a recipe for disaster. But did you know that combining alcohol with certain antibiotics is also a terrible idea? Bactrim, for example, is a popular antibiotic for treating ear infections, pneumonia, urinary tract infections, and similar problems. Drinking alcohol while taking Bactrim can cause vomiting, headache, shortness of breath, rapid heartbeat, profound fatigue, serious bone pain, and skin rashes. While taking Bactrim, adding even a cough remedy or mouthwash containing a bit of alcohol can cause this type of reaction. So if you like to enjoy a cocktail or glass of wine at the end of the day and if you have been prescribed an antibiotic or other medication, be sure to ask your physician about the possibility of an alcohol-drug interaction.

Here’s a partial summary of how alcohol and drugs affect each other:

  • Alcohol can boost a drug’s availability in the body, adding to the likelihood of negative complications.
  • Alcohol can essentially cancel out a drug’s effect.
  • Certain drugs may enhance the effects of alcohol. In this case, just a drink or two can have the same result as downing several times that amount.
  • Alcohol can combine with some drugs to create toxins that may harm the liver, kidneys, or other organs.
  • The effects of alcohol may interfere with drugs even when an individual is not drinking. For example, if a heavy drinker stops ingesting alcohol, it could take weeks for some medications to work.

Alcohol interacts with many drugs (see partial list below), and sometimes the consequences can be quite serious, especially for individuals with kidney or liver complications.

Some drugs that may interact with alcohol include:

  • Certain antibiotics, including Flagyl (metronidazole) and Furoxone (furazolidone)
  • Anticoagulants, such as Coumadin (warfarin)
  • Antidepressants, especially tricyclic antidepressants like Elavil (amitriptyline)
  • Antihistamines, such as Benadryl (diphenhydramine)
  • Heart and high blood pressure medications, including nitroglycerin and Inderal (propranolol)
  • Pain relievers, both prescription and nonprescription, including aspirin
  • Sleep aids and tranquilizers, such as Ativan (lorazepam) and Dalmane (flurazepam)

This is only part of a much longer list of drugs that interact with alcohol. That’s why it’s so important to talk to your physician or pharmacist about potential alcohol-medication interactions before combining the two.

Drugs and Food

There are two primary concerns when it comes to combining drugs and food. One is that a number of medications must be taken with or without food to be effective. Generally, this is clearly marked on the bottle. Some drugs, for example, can cause nausea or an upset stomach if taken on an empty stomach, so you’ll be instructed to take it with food. In other cases, food may interfere with absorption of a pill, so you’ll be instructed to take it on an empty stomach. Please follow these instructions carefully.

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The second primary concern is that certain foods may affect how the body processes the medication. Several types of citrus are good examples — most notably, grapefruit and its juice, along with a grapefruit relative known as pomelo, and Seville oranges. These fruits contain compounds that affect the way the body metabolizes particular drugs, including some immunosuppressants that are often given to transplant patients. Combining medications with these citrus fruits could cause the drug to remain in the body. As you continue taking your regular dose, the amount of the drug accumulates. Eventually, drug levels could reach the point of causing an inadvertent overdose.

If you are taking medication that interacts with grapefruit or other citrus fruit, you’ll need to stop eating or drinking the citrus completely. Taking the drug at a different time than the food or drink is not enough to prevent this potentially serious side effect.

Here is a partial list of drugs that may interact with grapefruit:

  • Zoloft (antidepressant also sold as sertraline)
  • Allegra (antihistamine also known as fexofenadine)
  • Procardia, Nimotop, Sular (calcium channel blockers also sold as nifedipine, nimodipine and nisoldipine)
  • Statin drugs like Lipitor, Zocor, Mevacor (also known as atorvastatin, simvastatin, and lovastatin, respectively)

Since research in this area is ongoing, be sure to check with your pharmacist about drug interactions every time you fill a prescription.

It’s simply impossible to list all of the potentially harmful drug-food combinations. To help you understand the scope of the problem, consider the following two common medications and the issues that may result from combining them with certain foods.

  • Warfarin (Coumadin) and foods high in vitamin K: Foods high in vitamin K (spinach, broccoli, kale, and other leafy greens) may interfere with the effectiveness of the blood thinner warfarin (also known as Coumadin). If you’re a regular salad eater, it’s fine to continue. But a sudden increase in leafy greens could cancel out the drug’s benefits.
  • Antibiotics and dairy products or calcium supplements: Dairy products or calcium supplements may inhibit the absorption of antibiotics. This is especially likely with the group of antibiotics known as quinolones (sold as Cipro, Avelox, Factive, Tequin, Floxin, and Levaquin). To avoid this problem, take the antibiotics at least two hours prior to taking supplements or four to six hours after taking them.

Drugs and Nutritional Supplements

Vitamins, minerals, and herbal supplements are increasingly popular as more and more people discover the downsides of drugs. For some individuals, that means mixing nutritional supplements with various medications. Again, it’s best to check first with a pharmacist or a well-informed physician who has some familiarity with nutritional supplements.

  • Blood pressure medications and potassium supplements: Taking potassium supplements with any of several different blood pressure medications (including ACE inhibitors, diuretics, or beta-blockers) could lead to dangerously high potassium levels, a condition known as hyperkalemia. Symptoms include nausea, weakness, heart arrhythmia, and fatigue. If you’re taking blood pressure medications, talk with your health-care provider before adding potassium supplements.
  • Blood thinners and garlic, ginger, curcumin, or ginkgo biloba: Combining these supplements with blood thinners such as Plavix or warfarin (brand name Coumadin) may cause blood to become too thin.
  • Diabetes medication chlorpropamide and garlic supplements: Mixing garlic supplements with chlorpropamide could cause blood sugar levels to drop.
  • Corticosteroids and licorice supplements: Taking licorice supplements, a natural cough or cold remedy, with corticosteriods may increase blood pressure and may also amplify the effects of the corticosteroids.

Drugs and Other Drugs

Here again, there is simply no way to cover all possible drug-drug interactions. There are literally thousands of different prescription and over-the-counter medications plus thousands of herbal and vitamin formulations. That’s why it’s so important to carry a list of all the medications and supplements you are taking whenever you go to the doctor or pharmacy. Yes, I am repeating myself, but only because this information may save a life or avoid a medical catastrophe.

This is a partial list of some of the drugs that commonly cause unwanted interactions:

  • Benzodiazepines (antidepressants)
  • Diuretics, beta-blockers, and calcium channel blockers used to treat high blood pressure and heart disease
  • Pseudoephedrine and ephedrine, common ingredients in cough and cold medicines
  • Blood thinners such as Coumadin (warfarin)
  • Steroids like prednisone
  • Nonsteroidal anti-inflammatory drugs (NSAIDs), including ibuprofen
  • Digestive aids with H2 blockers, such as Tagamet (cimetidine)

As you can see, the list covers a variety of drugs for various conditions, so it’s difficult to create a good rule of thumb. It’s up to you to always ask if a medication or supplement is compatible with what you’re already taking.

As I’ve said before, drugs are lifesavers in certain situations, especially in the short term, for something like knocking out an infection. But many people are convinced they need medications day in, day out for the rest of their lives, when perfectly acceptable natural alternatives are easier on the body, get the same results, and may eliminate concerns about drug interactions.

Meanwhile, if you are taking a medication, please take a few minutes to look over the drug insert, especially the section on dosage and possible side effects. Sometimes side effects do not appear for months after starting a drug. If you do begin to experience a new symptom, ask your physician or pharmacist if it could be a side effect of a drug you’re taking. Often, there are alternative medications that may not affect you the same way.

Furthermore, be sure that each of your doctors knows exactly which drugs and supplements you’re already taking, so there’s no accidental duplication or risk of getting incompatible prescriptions. In other words, monitoring your medication is an excellent place to start taking charge of your own health and playing an active role in your wellness.


Last Updated: May 1, 2019
Originally Published: September 10, 2012