You don’t make meth from benadryl. You make it from Sudafed.
How do you get down from an elephant?
That is the common thinking. Do you really know for sure. I’m not a chemist, are you.
There are several articles that would suggest you may be wrong. We have to be on the constant watch for the meth addicts where I live in Appalachia Ohio. https://www.seattlepi.com/news/article/Meth-problem-hits-feed-stores-food-plants-1087177.php