Skip to main content
Supplement ScienceSupplementScience

Herb-Drug Interactions: An Overview

This content is for informational purposes only and does not constitute medical advice. Statements about dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease. Individual results may vary — consult your healthcare provider before starting any supplement. Full disclaimer

Herbal supplements can change how medicines work — making them stronger, weaker, or riskier.

Herbal supplements can change how medicines work — making them stronger, weaker, or riskier. St. John's wort is the most notorious, weakening many drugs, while others like ginkgo and garlic can add to bleeding risk. Because 'natural' doesn't mean interaction-free, tell your provider about every herbal product you take.

Key Takeaways

  • Herbal supplements can increase, decrease, or dangerously combine with medications.
  • St. John's wort is the most notorious, weakening many drugs and raising serotonin-syndrome risk.
  • Ginkgo, garlic, ginger, and high-dose fish oil can add to bleeding risk with blood thinners.
  • Interactions are either metabolic (can't be spaced away) or additive (compounding a drug's effect).
  • Tell every provider about herbal products and ask a pharmacist before combining with medicines.

Get the free evidence-based Herb-Drug Interactions: An Overview guide — delivered in 60 seconds.

No spam. Unsubscribe anytime.

Herbs are biologically active

Herbal supplements contain active compounds, so it's no surprise they can interact with medications. NCCIH frames the three possibilities clearly: a supplement can increase a drug's effect, decrease it, or interact in harmful ways [1]. Herbs do this mainly by affecting drug-metabolizing enzymes or by adding to a drug's own action.

The herbs most likely to interact

  • St. John's wort — the standout. It speeds up drug-metabolizing enzymes and can weaken many medicines, including birth control, some heart, HIV, cancer, and transplant drugs, and it raises [serotonin syndrome](/learn/serotonin-syndrome-and-supplements) risk with antidepressants [2]. See [St. John's wort interactions](/learn/st-johns-wort-drug-interactions).
  • Ginkgo, garlic, ginger, and high-dose fish oil — can add to bleeding risk with blood thinners (see [supplements and blood thinners](/learn/supplements-and-blood-thinners)).
  • Ginseng — can interact with several drugs, including blood thinners and diabetes medicines.
  • Kava and valerian — add to sedation from other depressants.

Two main mechanisms

  • Metabolic interactions: the herb changes how fast the body breaks down a drug (St. John's wort speeds it up; [grapefruit](/learn/grapefruit-and-supplement-interactions) slows it). These can't be fixed by spacing doses.
  • Additive interactions: the herb adds to a drug's effect (bleeding, sedation, blood-sugar lowering).

Practical guidance

  • Tell every provider about all herbal products — they're often left off medication lists.
  • Be especially careful if you take blood thinners, antidepressants, transplant or HIV medicines, or have surgery coming up.
  • Don't assume 'natural' means safe to combine — see [why natural doesn't mean no interactions](/learn/why-natural-doesnt-mean-no-interactions).
  • Ask a pharmacist before adding any herb to a medication regimen.

Related Supplements

St. John's WortGinkgo BilobaGarlic

Related Conditions

DepressionAnxietyMood SupportSleepStressBrain Fog & Focus

Product Reviews

Best St. John's Wort Supplements
See our ranked picks →

Related Articles

Serotonin Syndrome and Supplements (5-HTP, St. John's Wort, SAMe)
St. John's Wort Drug Interactions
Supplements and Birth Control: The St. John's Wort Warning

Frequently Asked Questions

Which herbal supplements interact with the most medications?

St. John's wort is the standout, weakening many medicines including birth control and some heart, HIV, cancer, and transplant drugs. Ginkgo, garlic, ginger, and high-dose fish oil can add to bleeding risk, and ginseng, kava, and valerian have their own interactions.

How do herbs interact with drugs?

Mainly two ways. Metabolic interactions change how fast the body breaks a drug down — St. John's wort speeds it up, grapefruit slows it — and can't be fixed by spacing doses. Additive interactions add to a drug's own effect, such as extra bleeding risk or sedation.

Is it safe to take herbs with my prescription medicines?

It depends on the herb and the drug, so it shouldn't be assumed. Some combinations are fine, others are risky, and a few are dangerous. Tell your provider and pharmacist about every herbal product, especially if you take blood thinners, antidepressants, or transplant or HIV medicines.

Does 'natural' mean an herb won't interact?

No. Herbs contain active compounds, which is exactly why they can interact with medicines. 'Natural' says nothing about interaction risk — St. John's wort, one of the most potent interactors known, is a plant sold over the counter.

Continue Reading

Supplement Guide

St. John's Wort

St. John's Wort (Hypericum perforatum) has been studied in clinical trials for mild-to-moderate depressive symptoms; a Cochrane review of 29 RCTs found it superior to placebo. Standard dosing is 900mg/day (standardized to 0.3% hypericin) in 3 divided doses. CRITICAL: it is a potent inducer of CYP3A4 and P-glycoprotein and has serious, sometimes life-threatening interactions with SSRIs/MAOIs (serotonin syndrome), oral contraceptives (failure), anticoagulants like warfarin, HIV antiretrovirals, and immunosuppressants — never start without prescriber review of every medication you take.

Product Comparison

Best St. John's Wort Supplements

Condition Guide

Depression

References

  1. National Center for Complementary and Integrative Health (2026). How Medications and Supplements Can Interact. U.S. National Institutes of Health.
  2. National Center for Complementary and Integrative Health (2025). St. John's Wort: Usefulness and Safety. U.S. National Institutes of Health.