How does a doctor determine which drug is right?

There are clear protocols for this. For example, for fading aging skin, and a relatively healthy person without chronic systemic diseases, complex preparations are used. If the patient has rosacea, dermatitis or other skin diseases, then these will be preparations specially created for treatment containing superoxide desmutase, succinic acid and other ingredients aimed at regeneration. And for a young patient with the first signs of age-related changes, a drug with two forms of hyaluronic acid at once is suitable, because the main task is moisturizing.