So there are two totally different definitions of neurotoxic used in the medical field?

No, the scientific field uses it differently than the layman.

Neurotoxic to a scientist means “can have negative impact to brain function, whether temporary or permanent”.

The layman thinks neurotoxic means “kills your brain cells”.

What makes you think any of us were using the lay definition?

Because if someone said “opioids are neurotoxic” from a scientific definition, it’s stating the obvious.

Both definitions are correct.

From Wikipedia:

> Neurotoxicity is a form of toxicity in which a biological, chemical, or physical agent produces an adverse effect on the structure or function of the central and/or peripheral nervous system. It occurs when exposure to a substance – specifically, a neurotoxin or neurotoxicant– alters the normal activity of the nervous system in such a way as to cause permanent or reversible damage to nervous tissue.

Brain cells getting killed is a normal process, you could call it pruning. Cells grow back, you know!