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What Are ADEs (Adverse Drug Events)?

doctor and patient reviewing pills for what are ADEs

Most people take their prescription medications without too much thought. You assume the medications are going to work and that your care team has prescribed you the right ones to help solve your medical needs. But for many people who take one or more prescription medications at a time, taking them could mean danger is right around the corner if proper precaution is not taken.

What are ADEs? Adverse drug events (ADEs) are situations in which you are harmed by a medication or a combination of medications. According to the U.S. Department of Health and Human Services, ADEs could result in everything from respiratory issues (opioids) and bleeding (anticoagulants) to hypoglycemia (diabetes drugs).

Older adults make nearly 450,000 trips to the ER each year, which is more than twice the number of visits by younger people.1 Because older adults are more susceptible to ADEs, they are almost seven times more likely than their younger counterparts to be hospitalized after seeking emergency care. In part, this is because they often take multiple medications.2

Why are older adults more susceptible to ADEs? “Because of the ways they metabolize the medications,” says Nicole Brandt, PharmD. She’s a professor of pharmacy practice and science at the University of Maryland School of Pharmacy and executive director of the Peter Lamy Center on Drug Therapy and Aging. Brandt is also a practicing pharmacist who cares for older adults at the MedStar Center for Successful Aging in Baltimore, and she has extensive experience managing the risk as well as the impact of ADEs.

“Older adults often have multiple medical conditions, multiple medications, and multiple prescribers,” says Brandt.

If you’re wondering, “older adults” generally means anyone over the age of 65, “but we’re seeing certain populations, 75 and older, 85 and older, at even greater risk because of some of the ways they metabolize or eliminate medications,” says Brandt.

She adds that babies, children, and adolescents may also be at a higher risk of ADEs because of how they metabolize medications.

In short, ADEs are a serious medical issue. Here’s what you need to know to stay safe — and get the treatment you need.

What are ADEs (Adverse Drug Events)?

Adverse drug event (ADE) is an umbrella term that refers to any type of unexpected, potentially harmful event that happens after you take a medication, whether it be during appropriate or inappropriate circumstances.3

ADEs also have several related subcategories, some of which do not involve human error:

  • Adverse drug reaction (ADR)/ Non-preventable ADE/ Side effect: When someone has an unwanted or harmful reaction after the administration of a drug or drugs under normal conditions of use. (The terms “adverse drug event” and “side effect” can be used interchangeably.4) For example, if you’re receiving cancer treatment, a common ADR could be anything from vomiting and drowsiness to skin reactions and alopecia (or sudden hair loss). ADRs are also suspected to be related to the drug or drugs themselves.4 There are two classifications of ADR: Type A and Type B.
    • Type A ADRs: predictable based on how the drug is known to work once it’s in your system. Most ADRs fall under the Type A classification.
    • Type B ADRs: cannot be predicted based on what is known about the drug.5

These ADE subcategories, on the other hand, may involve some degree of human error: 

  • Drug toxicity: An adverse effect of a drug that occurs because the dose or concentration of the drug in your bloodstream has risen above the range your prescriber meant it to reach.4 
  • Ameliorable ADE: The patient experiences harm from a medication that, while not completely preventable, could have been mitigated with timely, appropriate management.4 
  • Potential ADE: A medication error that does not cause any harm — either because the drug is intercepted before reaching the patient or because of luck.4
  • Preventable ADE: An adverse drug event in which an element of error is involved (example: an improper dose of a drug is administered to a patient).4 

How You Can Avoid ADEs

So how can you avoid an ADE? You’ve got several options. We’ve outlined 6 tips to help you avoid ADEs below. 

1. Speak up for yourself.

Brandt emphasizes that patient awareness and self-advocacy are critical tools for reducing ADEs. “Advocacy for one’s health care is really important,” she says. “There’s a lot of fragmentation in health care within the United States,” meaning patients must take an active role in navigating the health care system. (A recent study showed that more than 58% of patients visited more than one hospital in a single year.)

2. Communicate openly and transparently.

“If a patient notices a new symptom, they need to share that with their provider,” says Brandt. “We as providers — pharmacists, physicians, nurse practitioners, the medical team — need to listen better, because a complaint could be related to the medications. And we don’t want to get into the habit of starting new medications to treat those other adverse drug events.”

3. Don’t be afraid to ask for help.

Brandt notes: “Older adults may not have the cognitive capacity to understand and navigate all of the medication complexities, whether it’s accessing their medications, taking their medications, and understanding, ‘Why do I take them?’ it’s important for patients with cognitive impairments to have an advocate, as well as a caregiver who can help them.”

4. Keep a list of all your medications, vitamins, and supplements — and let your primary care doctor know regularly.

This is especially important if you see multiple specialists, says Brandt. “Patients often get medications from multiple sources, including online, where the medication may not be registered in electronic health records. While patients value convenience and discounts, “using one pharmacy or one pharmacy system is one way to prevent or avoid adverse drug events.”

And if you drink caffeinated beverages, smoke, or use CBD or marijuana in any form, add it to the list as well. “Marijuana has medicinal properties, and it does interact with other medications,” says Brandt. Caffeine and compounds in tobacco have been found to alter how your body metabolizes and/or absorbs medications.

That risk factor only increases when you’re taking more than one medication. Did you know that some drugs interact with others to cause ADEs? These can cause what is known as drug-drug interactions. One way to avoid potential drug-drug interactions is through medication management. Your health care provider can use a drug interaction checker to help you avoid drug-drug interactions, which is why ensuring they have a complete list of your medications is important.

5. Ask your doctor about how your genes may interact with certain medications.

Did you know that the FDA has put gene-related information on over 300 drugs?6 It can be difficult to pinpoint whether a drug is interacting with your DNA. One way to unlock this crucial information is through pharmacogenomic (PGx) testing by a company like Genomind. (You may also see it called pharmacogenetic testing.) This technology can help identify how your unique genetic code may impact different medications.

Pharmacogenomics is another way for clinicians “to see if the patients we’re caring for may be at an increased risk of adverse drug events because they’re not metabolizing the medications as well,” says Brandt. “There’s a lot of genetic variability among gender, age, and ethnicity that might influence the way patients metabolize medications.” Someone who metabolizes a drug slowly may experience drug toxicity as a result.

Your healthcare provider can also help manage drug-gene (and drug-drug) interactions through digital platforms such as Genomind’s precision medicine software, which was designed to work in tandem with PGx tests and help healthcare providers evaluate safer prescribing options with speed and precision.

6. Follow your doctor’s instructions.

It can be difficult to juggle multiple medications at the same time — or even a single medication. When your doctor tells you about the medication or medications they’re prescribing you, try taking notes and follow up if you have any additional questions, like what are ADEs you might want to watch out for?

When you go to pick up your prescriptions, your pharmacist may also provide you with a medication guide, which can work as an added layer of security. You can learn a lot about what you’re taking just by reading the fine print. You can also talk to your pharmacist. More often than not, they’ll be prepared to walk you through any questions you might have about the medications you’ve been prescribed. (We outline specific questions you can ask your doctor and pharmacist in our guide: How to Avoid Medication Errors.)

Your doctor may also want to administer blood tests to ensure that you’re taking a safe and effective dose of your medication, so be sure to stay up to date on those tests.

The Bottom Line

Ultimately, it’s your health care provider’s responsibility to reduce the likelihood of you having an ADE. But now that you know what are ADEs, you can also avoid ADEs by asking the right questions of your clinician or pharmacist when you’re prescribed a medication; and being a vigilant, proactive patient or advocate who takes an attentive role in medication management.


  1. Older adults make 450k trips to ER: Adverse Drug Events in Adults (2017)
  2. ADEs more likely in older adults: American Family Physician (2019). “Polypharmacy: Evaluating Risks and Deprescribing
  3. Definition of an ADE: Medication Errors and Adverse Drug Events (2019)
  4. Definitions of ADRs and all subcategories: Department of Health & Human Services Patient Safety Network Glossary (2022)
  5. Classifications of ADRs: Adverse Drug Reactions: Classification, Susceptibility and Reporting (2016)
  6. 300+ drugs with pharmacogenomic associations: Table of Pharmacogenomic Biomarkers in Drug Labeling (2021) 

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