Drug Interactions

What are drug interactions?

A drug interaction is an unwanted change in how a medication affects your body due to the presence of another substance (like food or another drug) or an underlying medical condition. Drug interactions may lead to the drug:

• Not working as well as it should (reduced effectiveness)
• Doing more than it’s supposed to (increased action)
• Causing side effects or toxicity

Any one medication can interact with a wide range of substances you might put into your body, including:

• Another medication, either prescription or over-the-counter (OTC)
• A dietary supplement like a vitamin, mineral or herb
• A food or beverage
• Alcohol
• Tobacco
• Recreational drugs

Besides interacting with other substances, a drug might not be safe for you due to your medical history. For example, certain drugs might help with one condition but worsen another or lead to unwanted reactions.

Drug interactions are usually temporary and manageable. For instance, your provider may adjust your medications or ask you to avoid certain foods or drinks.

But in some cases, they can seriously harm you or even be fatal. Learning if you’re at risk of drug interactions and taking action to prevent them can help you get the most benefit from treatment.

Who’s at risk for drug interactions?

Drug interactions can happen to anyone at any age, but they’re more likely to occur if you take multiple medications or have several health conditions.

Typically, as we get older, we have more chronic conditions and a greater need for medications. And the more chemicals and processes that are interacting inside your body, the greater the chance that something could go awry.

It’s a bit like hosting a dinner party. If you invite just a few friends who know each other well, things will probably go smoothly. But the longer your guest list, the higher the odds of some conflicts. Just like people at a party, medications can interact with other substances in ways that aren’t the friendliest.

And if you’re throwing a party for a friend, you’d probably run the guest list by them first. You can think of your medications list in a similar way — as something that you shouldn’t try to manage alone. It’s not always possible to know how a certain medication will affect your body on its own, let alone with other medications thrown into the mix.

That’s why it’s crucial to talk to a healthcare provider before you take any medication or supplement for the first time or make any changes to your existing list. Your provider will make sure you’re taking medications or supplements that are necessary, helpful and safe for you — both alone and in combination with each other.

What are the different types of drug interactions?

Healthcare providers generally divide possible drug interactions into these categories:

• Drug-drug interactions. A drug interacts with another drug.
• Drug-supplement interactions. A drug interacts with a dietary supplement.
• Drug-food/beverage interaction. A drug interacts with something you eat or drink.
• Drug-condition interaction. A drug leads to unexpected effects due to a medical condition you have.

Drug-drug interactions (drug-to-drug interactions)

Drug-drug interactions occur when one medication changes how another medication works in your body. This might mean:

• Two prescription drugs interact.
• Two OTC drugs interact.
• A prescription drug and an OTC drug interact.

Drug-drug interactions can also involve substances like tobacco, alcohol or recreational drugs. These substances can interact with a prescription or OTC drug that you’re taking, leading to unintended effects.

Drug-to-drug interactions can:

• Worsen drug side effects. This might happen if you take two drugs with the same active ingredient. For example, you might take a pain reliever and a cold medication that contains multiple ingredients, including acetaminophen (the active ingredient in Tylenol®). Your body now has more acetaminophen than it’s supposed to, and you may have heightened side effects or even toxicity.
• Reduce drug effectiveness. This might happen if two drugs antagonize each other, meaning they do opposite things in your body. For example, one drug might block certain proteins while the other drug stimulates them. This can keep one or both drugs from working as well as expected.
• Change how a drug works. Certain drugs affect how well your body can absorb (and therefore, use) other drugs. Some drugs can also change how well your liver can break down other drugs. As a result, your liver might break down a drug too quickly (making the drug less effective) or too slowly (making the drug more potent).

Because so many different drugs can interact, it’s essential to talk to a healthcare provider before taking any new medications, both OTC and prescription. Tell them your current medications and ask if the medication you intend to take is safe for you. Your provider will also need to know if you’re using alcohol, tobacco or recreational drugs. The more you can share with your provider, the better they can help keep you safe.

Drug-supplement interactions

Dietary supplements include vitamins, minerals and herbs you take to support your health. Certain dietary supplements may make some medications less effective. When a drug is less effective, it’s less likely to have an impact on your condition. On the other hand, some supplements may make a drug too strong. When a drug is too strong, it may cause side effects — and some of those can be serious.

So, which supplements are most likely to interact with your medications? One of the riskiest is St. John’s wort. This herbal supplement interacts with many drugs, sometimes, in dangerous ways. For example, taking both St. John’s wort and selective serotonin reuptake inhibitors (SSRIs) can lead to a life-threatening condition called serotonin syndrome.

Other supplements that may pose problems include:

• Garlic extracts, which can thin your blood and lead to excess bleeding when taken with warfarin or other blood thinners or after surgery.
• Goldenseal, which can interact with many different medications by changing how your liver processes them.
• Concentrated green tea supplements, which may interact with pseudoephedrine (a nasal decongestant found in many OTC cold and flu medications).

These are just a few examples. Before you take any supplement, at any time, you should talk to a healthcare provider to make sure it’s safe for you.

It’s especially important to talk to your provider about any supplements you’re taking or want to take if you’re:

• Taking a medication that has a narrow therapeutic range
• Going to have surgery

Medications with a narrow therapeutic range

When a medication has a narrow therapeutic range, or index, that means you need exactly the right level of the medication in your body. Just slight changes in the level (too high or too low) can be dangerous or even life-threatening. And some supplements could tip the scales in either direction.

Here are examples of such medications:

• Carbamazepine or phenytoin, which prevent and control seizures.
• Cyclosporine, which prevents your body from rejecting an organ transplant.
• Digoxin, which treats heart failure and atrial fibrillation.
• Warfarin, which prevents blood clots.

Supplements and surgery

Some supplements can make surgery riskier for you by:

• Affecting how other medications, like anesthesia, work
• Raising your risk of bleeding
• Affecting your blood pressure or heart rate

Even if a supplement is normally safe for you, it might not be safe as you prepare for surgery. Your provider will explain what drugs you need to stop taking before your surgery.

Drug-food/beverage interactions

Certain foods and drinks can change how a medication works inside your body. A food or drink might:

• Prevent your body from properly absorbing the medicine
• Change how the medicine moves through your body to get where it needs to be
• Increase metabolism (breakdown) of the medicine, making it less effective
• Decrease metabolism of the medicine, leading to adverse drug effects
• Prevent your body from clearing the medicine from your body when it should, leading to toxicity

You need your medicines to work as expected. When foods or drinks get in the way, you might have side effects or even serious complications. For example, if you take warfarin, you rely on the drug to protect you against blood clots. But a sudden increase in your vitamin K intake may prevent warfarin from working properly, in turn raising your risk of blood clots.

Common culprits for drug-food interactions include:

• Grapefruit. Both whole and in juice form, grapefruit can interact with over 85 different medications, including some statins and organ-transplant rejection drugs.
• Dairy. Dairy products can interact with levothyroxine, bisphosphonates and some antibiotics.
• Vitamin K. Vitamin K is a nutrient found in many foods, including leafy greens. But it can interact with warfarin, so you should monitor your intake under your provider’s guidance.
• Tyramine. This is a substance found in aged or fermented foods. It can interact with linezolid, isoniazid and MAOIs.
• Alcohol. People consume alcohol in beverage form, but it’s actually a drug that can interact with many different medications, including metronidazole, barbiturates, warfarin and acetaminophen.

Sometimes, you need to avoid any food for a certain number of hours before and/or after taking a medication. That’s because some drugs interact with any type of food and fail to work properly as a result. Other medications need to be taken with food — or even certain types of food, like those high in fat — in order to work properly.

Your healthcare provider may advise you to avoid certain foods or nutrients or adjust the timing or portions. They’ll also tell you if you should take certain drugs with food or on an empty stomach.

Drug-condition interactions

Also called drug-disease interactions, these occur when a drug you’re taking to help with one condition worsens another condition or otherwise causes unwanted effects.

For example, many medications can raise your blood pressure. If you’re already living with high blood pressure, that spike could be particularly dangerous for you. Nasal decongestants are one common culprit. Others include amphetamines, NSAIDs (like ibuprofen and naproxen) and some steroids (like prednisone).

Overall, you may face an increased risk of a drug-condition interaction if you have:

• Bladder control issues
• Diabetes
• Enlarged prostate
• Glaucoma
• High or low blood pressure
• Insomnia
• Stomach ulcer

How can drug interactions be prevented?

Here are some tips for preventing drug interactions:

• Keep an updated list of all of your medications and supplements.
• Talk to a healthcare provider before taking anything new and whenever questions or concerns come up.
• Establish routines for how you take your medications.

Making a medications and supplements list

Your healthcare provider may suggest a format or give you a chart you can fill out. In general, your list should include the following information for each drug or supplement you’re taking:

• The drug or supplement’s full name.
• Its active ingredients.
• The reason you’re taking it.
• The amount you take (dose) and when.
• How long you need to take it (for example, short-term antibiotics vs. lifelong blood thinners).
• Special instructions, like whether to take with food.
• The name of the prescribing doctor, when relevant.

This list will probably change over time. So, it’s important to update it any time there’s a change. Anyone involved in your care should have the most recent copy, including your primary care provider, specialists and pharmacists. Consider using just one pharmacy to simplify things.

For your own reference, keep copies of your list — one at home in a spot where you can refer to it whenever you need, and one to carry with you.

Talking with your healthcare provider

When it comes to avoiding drug interactions, communication is key. Make sure all of your providers, including any pharmacists you consult, know what drugs or supplements you’re taking. Always talk to a healthcare provider:

• Before taking a drug or supplement for the first time
• Before making changes to your medications or supplements
• If you don’t understand medication instructions or precautions
• If you miss a dose
• If you have new or changing side effects
• If a medication doesn’t seem to be working as expected
• If you have any questions or concerns about what you’re taking

We can’t emphasize that first point enough — it’s vital to check with a provider before you take something new. Even if it’s OTC. Even if you took it years ago. Our bodies and medical needs change over time. Your healthcare provider will advise you on what’s safe and helpful for you based on your current needs.

If your provider prescribes a drug or gives the green light on an OTC drug or supplement, make sure you understand exactly how to take it. Consider asking:

• How much should I take, and how often?
• Should I take it with food or on an empty stomach?
• What exactly does “empty stomach” mean in this context?
• What foods and/or drinks should I avoid?
• Do I need to stop taking any other medications or supplements?
• What side effects might I expect? When should I call you about these?

Staying organized

Staying organized and sticking to a routine can help you remember to take your medications at the right times. For example, you might:

• Keep a calendar in a visible spot — like on your desk or the fridge — that lists exactly what you need to take and when.
• Use a pill box. But be sure to keep it out of reach of children and pets.
• Set alerts on your phone to remind you to take your medication. But we all know that technology isn’t foolproof. Use written reminders, too, just in case.
• Tell someone else in your household when you’re supposed to take your medicines. They can serve as backup in case you forget or get distracted.

Where can I find a drug interaction chart?

There are many resources available online, including drug interaction checkers that let you type in a drug name and search for interactions. But proceed with caution. Online checkers and charts can be handy, but they’re not a substitute for talking to a healthcare provider.

Your provider can give you the most up-to-date information on drug interactions. They also know you and your medical history, so they’ll tailor advice specifically to your needs.