A state of high spirits or euphoria induced without the use of drugs; (hence) a naturally occurring substance (as guarana, etc.) said to have effects similar to those of manufactured euphoria-producing drugs.
Origin
1970s; earliest use found in TV Times (Brisbane).
Definition of natural high in US English:
natural high
noun
A state of high spirits or euphoria induced without the use of drugs; (hence) a naturally occurring substance (as guarana, etc.) said to have effects similar to those of manufactured euphoria-producing drugs.