Yes, it's very possible depending on what you want to achieve. To carry out an in-depth and excellent study, group your animals thus:
Group 1 : Normal control
Group 2: Positive Control (diseased group)
Group 3: Standard control (treated with drug from the market)
Group 4: 100mg/kg of Extract A
Group 5: 100mg/kg of Extract B
Group 6: 100mg/kg of Extracts A and B.
Group 7: 200 mg/kg of Extract A
Group 8: 200mg/kg of Extract B
Group 9: 200mg/kg of Extract A and B.
You can as well create more groups for higher doses such as 300mg/kg, 500mg/kg, etc., depending on the scope of your work. The whole essence of this is to ascertain whether the effect of the extract is synergistic and dose-depebdent.