Are you supplementing it in animal diets or what?. If animal diets, i suggest you start from very low dose like 0.05g, 0.1, 0.2, ........ may be upto 1g/100g. The reason is that plant extract when above 2 or 3 g, causes immunosuppression. Most literature recommended between 0.5-2.0g/100g depending on the model animal and plant extracts used.  

Do toxicity studies According to OECD guidelines. Once established toxicity choose 1/10 th of the highest safe dose for experimental setup. for eg if safe dose comes to be 5000mg/kg the effective dose will be 500mg/kg and so on.

hope this will help