*work in people = 人間に作用する、人間に有効、

Because both ingredients of this chemical cocktail are already approved by the FDA, Dr Conboy’s team is now planning a clinical trial of 20 volunteers over 65, to see if the cocktail’s rejuvenating power will work in people.

Ageing - Rejuvenation juice The Economist September 14th 2019 老化と若返り、不老薬

から