I’ve heard of functional nutrition, which is just another way of saying food supplements. Another common buzzword for this kind of thing is nootropics. Sounds more scientifical, innit.
It’s all snake oil. Try eating proper food instead.
Functional medicine is a new one on me. Medicine is highly regulated in the UK, so nothing that isn’t actually medicine is allowed to be labelled medicine. Although I expect this could be about to change if Truss lasts more than five minutes in the job.