there have been some important things brought up here so let me recap and add a few:

1. the smell. Is it giving off a strong smell of weed?
2. the size of the leaves suggest that it is not weed. I know that japanese maple have very similar leaves to marijuana that turn from green to red to purple, but i dont know why your friend would have one indoors.
3. What context is it in? if it is indeed being grown out in the open, in may not be weed, but under a professional grow setup, possibly.

If you see it again pay close attention to these details, and tell us what happens.