I've tossed old vitamins in my compost. The more volatile stuff will break down pretty quickly, but the micronutrients will remain. Hope they are available for plant use. I know there's that tiny brown bottle of a vitamin liquid for plants that I think is mostly B vitamins. With a healthy compost, you would probably already have B from yeast/fungal action on the periphery.
I put some broken up calcium tabs in a few pots this year, but haven't noticed any particular response.
A tiny part of my job is destroying old medications. There is a protocol for different sorts, but stuff like supplements are such a shame to waste. I also have a connection to two clinics in poverty and tragedy stricken environments so if it can be used by someone that's where it will go.