Oh gosh no! Some of the most natural things are deadly like bacteria and viruses. And some synthetic lab made compounds are really good for you (like pretty much all the vitamin C you take is made in factories).
There are also some mushrooms which contain deadly natural compounds. The appropriately named Death Cap and Destroying Angel mushrooms have compounds called amatoxins in them. If you’re unlucky enough to eat enough of those mushrooms, it can only take from between 6 and 24 hours for the symptoms to start showing. Amatoxin poison symptoms start with vomiting and diarrhoea and can lead to liver and kidney failure.
So make sure you know which are safe mushrooms if you’re ever out picking them! 🙂