Warnings & Interactions

Safety Classes

Class 1

Herbs that can be safely consumed when used appropriately.

  • History of safe traditional use
  • No case reports of significant adverse events with high probability of causality
  • No identified concerns for use during pregnancy or lactation
  • No innately toxic constituents
  • Toxicity associated with excessive use is not a basis for exclusion from this class
  • Minor or self-limiting side effects are not bases for exclusion from this class

Class 2

Herbs for which the following use restrictions apply, unless otherwise directed by an expert qualified in the use of the described substance:

2a: for external use only

  • Toxicity demonstrated with crude preparation taken orally at traditional dose
  • Adverse event data in humans with probability of causality of toxicity (eg. hepatotoxicity, nephrotoxicity, neurotoxicity) associated with oral use

2b: Not to be used during pregnancy

  • Traditional use contraindicates
  • Traditional use as an abortifacient or uterine stimulant
  • Relevant adverse even data in humans exist and have probability of causality
  • Data in animals suggesting teratogenicity or other adverse effects on the fetus or mother, with reasonable application to humans
  • For plants with common food uses, standard dose is in excess of typical food amounts

2c: Not to be used while nursing

  • Traditional use contraindicates
  • Relevant adverse event data in humans exists and has probability of causality
  • Potential hepatotoxicity or neurotoxicity
  • Bioavailability of constituents of concern in breast milk has been demonstrated

2d: Other specific use restrictions as noted

  • Information exists that use may be unsafe for specific populations
  • Dosage level outside of a standard range known to cause adverse effects

Class 3

Herbs to be used only under the supervision of a qualified expert. The following labeling is recommended for Class 3 herbs:

“To be used only under the supervision of an expert qualified in the appropriate use of this substance.”

Labeling must include proper use information: dosage, contraindications, potential adverse effects and drug interactions, and any other relevant information related to the safe use of the substance.

  • Narrow therapeutic range
  • Identified safety concerns in many populations


Interaction Classes

Class A

Herbs for which no clinically relevant interactions are expected.

  • No case reports of suspected interactions with probability of causality
  • No clinically relevant interactions in human pharmacological studies, if any,

Class B

Herbs for which clinically relevant interactions are biologically plausible

  • Human or animal pharmacological study data suggest potential for clinically relevant interaction.
  • Multiple case reports have suggested a potential interaction concern.
  • Cell culture or biochemical assays establish a basis for biologically plausible mechanism of interaction.

Class C

Herbs for which clinically relevant interactions are know to occur

  • Human pharmacological study has demonstrated interaction with a specific drug or supplement.
  • Human pharmacological study has demonstrated clinically relevant effects on drug metabolizing enzymes or drug transporter proteins.
  • Case reports of suspected interactions have a probability of causality.


All of our safety information is from:
The Botanical Safety Handbook. Second Edition. Edited by: Zoë Gardner, Michael McGuffin. Expert Advisory Council: Roy Upton, Soaring Bear, David Winston, Daniel Gagnon, Aviva Romm, Tieraona Low Dog, Mary Hardy, Lyle Craker