When you take multiple medications, each one can affect how the others work. Some interactions are minor; others can be dangerous. Understanding the basics helps you ask better questions and stay safer.

According to the National Institute on Aging, about one-third of adults in their 60s and 70s take five or more prescription medications—and the more you take, the higher the risk of interactions.

Here’s what you need to know.

Why Older Adults Face Higher Risks

Your body processes medications differently as you age. The FDA explains several changes that affect how drugs work:

  • Digestive changes affect how quickly medications enter your bloodstream
  • Body composition changes influence how long drugs stay in your system
  • Slower circulation affects how quickly drugs reach organs
  • Reduced kidney and liver function means drugs break down and leave your body more slowly

This means a dose that worked fine at 50 might be too strong at 75—and combinations that were safe before might become problematic.

Types of Interactions

Drug-Drug Interactions

When two medications affect each other, they can:

Increase effects (potentiation)

  • Two sedatives taken together can cause dangerous oversedation
  • Two blood thinners can dramatically increase bleeding risk

Decrease effects (antagonism)

  • One medication blocks another from working
  • A drug might speed up how quickly another leaves your body

Create new problems

  • The combination produces effects neither drug causes alone

Drug-Food Interactions

What you eat and drink matters too:

  • Grapefruit affects dozens of medications by slowing their breakdown, potentially causing overdose effects
  • Vitamin K (in leafy greens) can counteract blood thinners like warfarin
  • Calcium (in dairy) can reduce absorption of certain antibiotics and thyroid medications
  • Alcohol amplifies sedating effects and can damage the liver when combined with certain drugs

Drug-Supplement Interactions

Over-the-counter supplements aren’t always harmless:

  • St. John’s Wort can reduce effectiveness of many medications, including antidepressants and birth control
  • Ginkgo biloba increases bleeding risk when taken with blood thinners
  • Calcium and iron can interfere with thyroid medications
  • Fish oil may increase bleeding risk with blood thinners

Commonly Dangerous Combinations

GoodRx and other sources identify these high-risk combinations:

Blood Thinners + Pain Relievers

Warfarin + Aspirin or NSAIDs (ibuprofen, naproxen)

  • Both thin the blood
  • Combination significantly increases bleeding risk
  • Even occasional aspirin use matters

Opioids + Sedatives

Opioid pain medications + Benzodiazepines (Xanax, Valium, Ativan)

  • Both slow breathing and cause sedation
  • This combination can be fatal, even at normal doses
  • Also increases fall risk dramatically

Blood Pressure Medications + Potassium

ACE inhibitors (lisinopril, enalapril) + Potassium supplements

  • ACE inhibitors already raise potassium levels
  • Adding supplements can cause dangerously high potassium
  • Symptoms include muscle weakness and heart rhythm problems

Heart Medications + Antibiotics

Digoxin + Certain antibiotics

  • Several common antibiotics, including erythromycin and tetracycline, increase digoxin levels
  • Can lead to digoxin toxicity even at normal doses
  • Symptoms include nausea, vision changes, irregular heartbeat

Sleep Medications + Antibiotics

Zolpidem (Ambien) + Ciprofloxacin

  • The antibiotic slows breakdown of the sleep medication
  • Increases drowsiness, confusion, and fall risk

Multiple CNS Depressants

Any combination of:

  • Sleep aids
  • Anti-anxiety medications
  • Opioid pain relievers
  • Muscle relaxants
  • Antihistamines (like Benadryl)

The NIA warns: “In older adults, prescribing three or more CNS-active drugs may increase the risk of falls, overdoses, memory problems, and death.”

High-Risk Medications to Watch

According to research on multidrug interactions, these medications are frequently involved in serious interactions:

  • Amiodarone (heart rhythm)
  • Methotrexate (arthritis, cancer)
  • Warfarin (blood thinner)
  • Tramadol (pain)
  • Fluoxetine (depression)

If you take any of these, be especially vigilant about interaction checking.

Warning Signs of Interactions

Watch for these symptoms, which might indicate a drug interaction:

  • Unusual drowsiness or confusion
  • Dizziness or lightheadedness
  • Unexpected bleeding or bruising
  • Nausea, vomiting, or stomach pain
  • Changes in heart rate or rhythm
  • New or worsening symptoms
  • Medications not working as well as before

If you notice any of these, contact your doctor or pharmacist before stopping or changing medications on your own.

How to Protect Yourself

Keep a Complete Medication List

Include everything:

  • Prescription medications (name, dose, frequency)
  • Over-the-counter drugs (pain relievers, antacids, sleep aids)
  • Vitamins and supplements
  • Herbal products

Bring this list to every medical appointment and pharmacy visit.

Use One Pharmacy

Your pharmacist’s computer system checks for interactions—but only if they know about all your medications. Using one pharmacy for everything enables automatic screening.

Speak Up About New Prescriptions

When a doctor prescribes something new, ask:

  • “Will this interact with my current medications?”
  • “Should any of my other medications be adjusted?”
  • “Are there foods or supplements I should avoid?”

Be Cautious with OTC Medications

Just because something is available without a prescription doesn’t mean it’s safe with your other medications. Ask your pharmacist before taking:

  • Pain relievers (aspirin, ibuprofen, acetaminophen)
  • Cold and flu medications
  • Sleep aids
  • Antacids
  • Allergy medications

Request Regular Medication Reviews

Ask your doctor for a comprehensive medication review at least once a year—more often if you take multiple medications or have had recent hospitalizations.

Know About the Beers Criteria

The American Geriatrics Society Beers Criteria is a list of medications that may be inappropriate for older adults. Ask your doctor or pharmacist to review your medications against this list.

Questions to Ask Your Healthcare Providers

When getting a new prescription:

  • Does this interact with anything I’m taking?
  • What side effects should I watch for?
  • Is there a safer alternative?

At annual checkups:

  • Do I still need all these medications?
  • Can we simplify my regimen?
  • Should any doses be adjusted?

If you notice problems:

  • Could my symptoms be caused by a drug interaction?
  • Should we check my medication levels?

The Bottom Line

Drug interactions are a real risk, but they’re largely preventable. Keep your medication list current, use one pharmacy, communicate with your healthcare providers, and don’t assume over-the-counter products are automatically safe.

When in doubt, ask. Your pharmacist and doctor would rather answer questions than treat a preventable interaction.

OliveCare tracks all your medications in one place and helps you remember the questions to ask at your next appointment.