Key word there is SIMILAR. And it is produced within the body, not taken into the body. BIG differences. That's a neurochemical, not a drug, and the fact that it's similar to THC doesn't make THC a natural part of our bodily functions.
The stuff we have in our brain is identical to thc. We need it. We need it to manage pain and we need it to stimulate our appetite among other things. That is why marijuana is now an FDA approved medicine in the form of Marinol and a couple other trade names.