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Test Your Knowledge: Drug Interactions

Many Americans take both dietary supplements and prescription or over-the-counter drugs. Sometimes, these drugs and supplements may interact in unintended ways.

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Let’s test your knowledge and dig deeper:

Quiz Time:

  1. TRUE or FALSE Some supplements can decrease the effects of drugs.
  2. TRUE or FALSE Some supplements can increase the effects—including unwanted side effects—of drugs.
  3. TRUE or FALSE Some interactions between supplements and drugs are very dangerous.
  4. TRUE or FALSE Scientists know a great deal about drug supplement interactions.

1+2. It is true—supplements can both decrease and increase the effects of drugs.

EXAMPLE | St. John’s wort can decrease the effectiveness of birth control pills, leading to breakthrough bleeding and an increased risk of unintended pregnancy.

EXAMPLE | Herbs that decrease blood sugar may interact with anti-diabetes drugs to cause blood sugar to drop too low.

3. It is true—interactions between some supplements and drugs are very dangerous.

EXAMPLE | Interactions can decrease the effectiveness of critically important drugs—such as drugs that prevent transplanted organs from being rejected.

4. False. For many drugs and supplements, there’s little information on possible interactions.


One popular herbal supplement is especially well known for decreasing the effects of drugs. It does this by speeding up the processes in the body that change drugs into inactive substances. This herb may decrease the effectiveness of more than 70 percent of all drugs.

Quiz Time:

Which of these herbs is the one that decreases the effects of many drugs?

  •  Black cohosh
  •  St. John’s wort
  •  Saw palmetto
  •  Echinacea

St. John’s wort. In most instances, it speeds up the processes that change the drug into inactive substances, leading to a decrease in drug levels in the body. However, St. John’s wort interacts with some drugs in other ways.

EXAMPLE | Taking St. John’s wort with certain types of antidepressants can lead to a potentially life-threatening increase in the body’s levels of serotonin.

When people think about drug interactions, they often think about prescription drugs. It is important to remember that some drugs available over-the-counter can interact with supplements, too.

Quiz Time:

Which of these over-the-counter drugs may interact with herbal supplements?

  • Aspirin
  • Pseudophedrine
  • Fexofenadine
  •  All of them

The answer is “all of them”.

EXAMPLE | A variety of herbs that are known to possess antiplatelet activity may interact with aspirin to increase the risk of bleeding. Concentrated green tea supplements interact with pseudoephedrine. St. John’s wort interacts with fexofenadine (Allegra).

Working with Your Healthcare Providers

It’s important to tell your healthcare provider about all the drugs and supplements you take. Be sure to update this information every time you visit.

Helpful Hint:
Bring a written list of all of the drugs and supplements you take. Include how often you take them and the doses. You may even consider taking the product bottles to the provider’s office.

Quiz Time:

Besides your primary healthcare provider, which of these people need to know about all the drugs and supplements you’re taking?

  • Dentist
  • Any medical specialists (cardiologist, dermatologist, etc.)
  • Optometrist
  • Emergency or urgent care providers
  • Any complementary health practitioners (acupuncturist, chiropractor, etc.)
  • All of the above

The answer is “all of the above”.

Online Resources:
Dietary Supplement Fact Sheets
The National Institutes of Health

Drug Interaction Checker

The information contained within the checker should NOT be used as a substitute for the advice of an appropriately qualified and licensed physician or other healthcare provider.

Source Info: National Center for Complementary and Integrative Health
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