The quality and purity of Quantum Nutrition Labs supplements are fantastic! I have been using various supplements for over 20 years and I couldn't be happier. It is difficult to find quality supplements and Quantum Nutrition Labs never disappoints. The reason I am giving QNL 4 out of 5 stars is that at times, some of the previous supplements I would regularly order become discontinued. I am not sure what the reasons for this might be, i.e quality control, less customer demand...etc. A few items I miss are the progesterone cream, Quantum Tooth and Gum Support, and a product that used to be called Gold 360. This is my only complaint. I have not found a cleaner, pure, high-quality source of supplements than QNL.