I have dark patches around my mouth, upper lip, forehead and neck. Can I use a hydroquinone 4% w/w cream for this?

Dark patches on the face can be upsetting, especially when they're this visible, so I understand wanting a quick fix. Hydroquinone 4% is indeed one of the more effective options for stubborn pigmentation, but it's also potent enough that it needs careful use - the right duration, sun protection, and sometimes breaks in between to avoid irritation or rebound darkening. Since what you're describing could be melasma or another type of pigmentation that responds differently to treatment, it would help to see a dermatologist first so they can confirm the diagnosis and guide you on how long and how often to use it.