This is absolutely not true, FRiend, and belies an ignorance on the subject.
There are components in cannabis that are just now being studied; much of the study is driven by legalization in CO. The state mandated testing to confirm what is in the products being sold.
Most of these components are naturally occurring in other plants. For instance Linalool: It is the thing in Lavender that people find relaxing and calming.
Another example: Myrcine: This is also found in mangos and temporarily weakens the blood-brain barrier. That alone has profound medical importance.