They started as medicines and were concentrated, distilled, and extracted to the point where the medicine it became was deadlier than the cure it provided.

Coca leaves are still consumed medicinally/recreationally in some parts of south america.

Poppy seeds have a whole history of being abused and weaponized through the silk road.

Marijuana has faced a similar story, though without the deaths. This hasn't stopped governments around the world from conflating the deaths caused by other things with the use of medicines that in no way cause death.