Isotonic vitamins are supplements in liquid form that have been aggressively promoted on the Internet as being better absorbed and therefore more effective than ordinary vitamins in tablet form. The word "isotonic" means that the liquid containing the vitamins has the same solute concentration as bodily liquids such as blood and saliva. That may be a clever way to market these supplements, but there is no scientific evidence to support the notion that vitamins in liquid form are any better for you than conventional tablets. In fact, because liquid vitamins tend to oxidize more readily, they actually may be less stable than vitamins in capsule or tablet form.
Although I do see a need for good quality liquid vitamins - for people who can't swallow pills easily or don't like taking them, for example - I haven't been impressed with many of the liquid products on the market today. What's more, liquid vitamins are usually much more expensive than other forms.
Beyond the unwarranted claims that they're better for you is the fact that some isotonic supplements are sold through multilevel marketing - you buy them through distributors who make money not only through their own sales but also through those of the people they recruit. I am on record as being against multilevel marketing strategies. They are nothing other than pyramid schemes that enable those at the top to profit by leaving those at the bottom empty handed.
Andrew Weil, M.D.