I've been using Flexacil Ultra for my knees for years and over the years there's been a couple of times where I ran out and didn't reorder thinking I didn't need them any longer, then as a week or two would pass I would be climbing some steps and really feel the difference (pain) without the Flexacil Ultra. I also showed the ingredients to my doctor and he gave it the "thumbs up." I've always purchased these on Amazon, however, the last time I tried to purchase the 3-pack it was unavailable and the only thing available was a single bottle for a ridiculous price so I went direct to the Flexacil Ultra website and they had the 3-pack for the same price as Amazon and also with free delivery like Amazon. I have thinning cartilage in my knees and I highly recommend Flexacil Ultra.