There was never a time when naturally occurring plants were not considered possible sources of pharmacological agents.
However the big push for magical Eastern medical theories created the myth of Chinese Herbal Magic, that is being resurrected by the ignorant BS press in the wake of Dr. Tu’s Nobel prize in Medicine.
All the media are Channeling the Eastern Mystical stuff again. What’s your mantra?
Plants can contain poisons and pharmacological agents, sometimes the poison/drug effect is just dose related–remember Paracelsus. For example Oleander is poisonous because it has a cardioglycoside that also is beneficial in the right dose.
Josh Bloom provides the real story of Dr. Tu’s nobel achievement. It was Chinese but not Magical Chinese, it was scientific Chinese. Using modern Chemical and Pharmacological methods.