Morphine, from which heroin is derived, codeine and thebaine come directly from a plant. Many prescription pain killers like hydrocodone are derivatives of the latter compound.
Chewing coca leafs is healthy and I guess close to impossible to overdose, but if you take a condensed and highly extracted version of that, cocaine, you can very easily overdose.
I heard rumors that in russian prisons people make this condensed coffee drink that acts as a sort of meta-amphetamine replacement. They basically make coffee out of coffee until it's this sticky black thing that gets you really driven, I don't remember what they call it, but I remember many people die from this substance also.
Same thing with natural plant vs chemical extracts. Much easier to overdose and get lethal dosage.
Probably, you are referring to the "chifir": https://en.wikipedia.org/wiki/Chifir' It is prepared by boiling tea leaves, rather than coffee beans. Chifir is indeed a stimulant, although totally unrelated to methamphetamine (which, by itself, is not popular or easily obtained in Russia at all).
One point of contention I'll raise is that with self-grown anything one can control what adulterants are added.
A particular problem with opioid overdose is the tendency for opioid pain killers to have paracetamol/acetaminophen/APAP/Tylenol added, which when taken in large doses will cause permanent liver damage.