Abstract: Seventy-nine injectable herb extractions have been approved by the Chinese Food and Drug Administration (CFDA) and are frequently administered intravenously for various diseases. Unfortunately, herb-drug interactions are under-investigated and sometimes overlooked in the clinic. In the present investigation the in vitro inhibition of 9 drug metabolizing enzymes including CYP1A, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A was assessed using an appropriate probe substrate for each enzyme with human liver microsomes. Metabolite formation was quantified using a validated and sensitive high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay. The IC₅₀ of each herb extract was estimated using a concentration range from 5% to 0.5%, and the time-dependent inhibition of the nine CYP450 isoenzymes was also determined. Of the 79 approved iv herb injectables, 37 inhibited CYP1A, 24 inhibited CYP2A6, 41 inhibited CYP2B6, 36 inhibited CYP2C8, 31 inhibited CYP2C9, 41 inhibited CYP2C19, 13 inhibited CYP2D6, 25 inhibited CYP2E1, and 42 inhibited CYP3A with 50% or greater inhibition at a test concentration of 5% (v/v). IC₅₀ differences were noted between pre-incubation or co-incubation assays with HLM for 30 min, with the time-dependent inhibitory (TDI) effects were observed with 2 injectables on CYP1A, 5 injectables on CYP2A6, 5 injectables on CYP2B6, 6 injectables on CYP2C8, 1 injectable on CYP2D6 and 6 injectables on CYP3A. Collectively, the results demonstrate that potential herb-drug interactions (HDIs) can occur with the concomitant use of herb injectables and prescription drugs that are cleared by CYP450 enzymes, and further investigation is warrant for the clinical relevance of these interactions.