Glutathione levels can drop due to oxidative stress - the imbalance of free radicals and antioxidants in your body, and low vitamin E and alpha-lipoic acid intake
Hydration levels and healthy heart rhythm and contraction.
While glutathione supplements are broadly suitable for almost anyone who wants to increase their body's capacity to combat oxidative stress, they can best serve individuals who wish to prevent, delay, or alleviate specific chronic health conditions associated with glutathione depletion:15 Neurodegenerative disorders such as Alzheimer's and Parkinson's Respiratory diseases like asthma and COPD Cardiovascular diseases like hypertension and high cholesterol Age-related diseases like cataracts, macular degeneration, and hearing impairment Immune diseases like HIV and AIDS Liver disease Cystic fibrosis Additionally, because the goal is to reduce oxidative stress, people who are regularly exposed to ROS-generating compounds (e.g., smoke, alcohol, and sunlight)23 might consider adding glutathione to their supplement rotation, at least to help counter the effects of oxidative stressors

Because GHK-Cu stimulates the skin's own collagen-producing machinery rather than temporarily plumping the surface, the firmness improvement is structural it's still there months later, not gone the moment a filler effect wears off
The effectiveness depends on dosage, formulation, and medical supervision
Journal of physiology and pharmacology : an official journal of the Polish Physiological Society