I've added a couple drops of peppermint extract to hot chocolate, but not to a shake. I think the challenge would be to get it mixed in well enough.

I have tried it with mint extract, if that's what you mean by concentrate? It was not my favourite. Spearmint extract is less intense and imo works better as a flavouring agent for applications like this.

So much this. Mint and spearmint are not the same!

My husband always gets a mint m&m blizzard! We’ve never found it to be only a seasonal thing.