will l carnitine affect sleep L-Carnitine and Sleep: Does It Rest or Quality? Carnitine in Human Muscle Bioenergetics:

It cannot be used as food, dietary supplement or medicine

A 2008 laboratory study examined the combination of niacinamide and retinoic acid (what retinol converts to in your skin) and found that niacinamide significantly reduced the irritation and dryness caused by retinoic acid [1]

PubMed Pairs well with Tocopherol Tocopheryl Acetate Niacinamide Hyaluronic Acid Ceramides Glycerin Centella Asiatica Extract Rosmarinus Officinalis Extract Avoid combining with Benzoyl Peroxide Vitamin C (L-Ascorbic Acid) at high pH AHA/BHA (concurrent use may increase irritation) Tretinoin Adapalene Isotretinoin INGREDIENT ANTIOXIDANT, ANTI-AGING, SKIN BRIGHTENING Ascorbic Acid also known as Vitamin C Function Antioxidant protection, collagen synthesis support, and melanin regulation How it works Ascorbic acid functions as a free radical scavenger, reducing oxidative stress that contributes to photoaging and hyperpigmentation

What does vitamin C do for your face in terms of anti-ageing

Since this 2012 publication, there has been very little new research into this question