That was my initial reaction at first as well. However as far as I can tell, natural products are not patentable, unless the product in question has been modified, manipulated etc, to produce something that is deemed to have been significantly changed.
So, in the US, for example, the Supreme Court ruled that human DNA, being a naturally occurring product, cannot be patented. However, it also ruled that complementary DNA, essentially DNA that has been extracted and then modified in a lab, can be patented.
Thanks for clarifying. Although I don't agree with your doctor friend from an ethical standpoint, the point about natural products not being patentable is an interesting one and hadn't occurred to me before.
Medicine is any substance that has a demonstrable healthcare effect (demonstrated through double blind tests and not some rando's anecdote). That includes natural substances.
To put it another way, medicine and natural substances are not two mutually exclusive (i.e. disjoint) sets, as you and/or your doctor friend appear to be implying.
Normally black holes are considered to be everything up to the event horizon. E.g., from the Wikipedia page:
The term "black hole" derives from the fact that beyond a certain point light can't escape, that point being the event horizon.