Table 2.

Quality of HDI evidence for clinical risk assessment.

Level	Description of evidence
1	Published theoretical proof or expert opinion on the possibility of HDI due to certain factors including the presence of known interacting phytochemicals in the herbs, structure activity relationship
2	Pharmacodynamic and/or pharmacokinetic animal studies; in vitro studies with a limited predictive value for human in vivo situation
3	Well documented, published case reports with the absence of other explaining factors
4	Controlled, published interaction studies in patients or healthy volunteers with surrogate or clinically relevant endpoint