Another thing... the fact it turned green seems to suggest you ate the eliminated product, throw in double bonds particularly conjugated ones like you had and organic compounds tend to turn colors. Perhaps you have been the one to prove the safety of these compounds - you're still walking and talking and you probably ate a solid dose of that shit.

It's really hard to acylate tertiary alcohols without acyl anhydrides or acyl chlorides... especially given elevated temperatures... you probably just eliminated water from loperamide. It's unlikely it was acylated...

I agree, that solution would have been too acidic and would likely have dehydrated the tertiary benzylic alcohol. Note that the pure anhydride lacks an acidic hydrogen and is therefore unable to remove water in the acid-catalyzed dehydration reaction.

I read about a case where some guy got Parkinson's after consuming homemade MPPP contaminated with MPTP after using old propionic anhydride that had absorbed water and became "wet propionic anhydride" (actual term used), which to me means that most of the anhydride had turned into the acid.

I believe that the best way to prevent this (say if using anhydride that contains a fair percentage of acid) is to use an acid-scavenging cosolvent like pyridine or triethylamine. The upside to this is that the base exerts a catalytic effect and less anhydride is needed.