they are potentially detrimental

It's not wrong but doesn't follow the strictest grammatical sense that might make it clearer. However, the fact is that caffeine is an inanimate object. A person is unlikely to use 'whose' as modifier.

For a more clearly understood phrase, I suggest:
"they are potentially detrimental to caffeine-sensitive people , whose ..."

More of the sentence would help, Tintin. Modifiers are often close to what they modify but they don't have to be.

they are potentially detrimental to people who are sensitive to caffeine, [those people] whose metabolism is adversely affected by increased blood pressure.

beautiful . That helped me