You always start with in vitro toxicity. Search the net for in vitro or in silico toxicity studies and you will find an abundance of references.

It depends on what type of leaf extract you are using. If the extract is too toxic, toxicity study on animals is necessary..

There are other methods which you can source for on the internet but if the extract is a drug candidate, I guess you can't run away from animal tests.

Thank you so much for valuable info on this. I'm starting to find this subject very interesting & challenging