**3.5 Echinacea pharmacokinetics**

In vivo pharmacokinetics in 12 healthy men and women, *Echinacea purpurea* root inhibited CYP1A2 and induced CYP3A enzymes [36]. In another similar study with 13 healthy adults, *Echinacea purpurea* induced CYP3A enzymes but did not change the pharmacokinetics of ritonavir. Ritonavir is an inhibitor of CYP3A thus likely counteracted the induction caused by echinacea. No effect on p-glycoprotein was found [37]. In an in vitro study, *Echinacea purpurea* showed mixed effects on CYP3A4 and moderate inhibition of CYP2C9 [38]. A review article found echinacea to have high likelihood of drug-herb interaction [39].

#### **3.6 Echinacea safety summary**

Echinacea is likely safe when taken short-term, up to 8 weeks, in healthy adults. Unknown safety in patients with diabetes or heart disease. Caution should be taken when combining with medications metabolized by CYP3A, 1A2, and 2C9 enzymes.
