Fizzies were developed by Lem Billings, a chemist. He probably got his inspiration from Alka-Seltzer, which came in a tablet the effervesced when dropped in water* Billings developed a tablet that did the same thing -- but turned into a fruit-flavored carbonated soft drink. The product was introduced by the Emerson Drug Company and eventually bought and marketed nationally by Warner Lambert.
Fizzies came in six main flavors: orange, cherry, grape, lemon-lime, strawberry, and root beer.** Each package contained eight tablets. You'd just drop them into a glass of water and you'd have an instant soft drink.
At least, that was how they were supposed to work. The problem was that the tablet was not big enough to flavor a full glass of water***. So, as a kid, you'd drop a tablet into the water and watch it fizz and color the water, but it tasted only vaguely of fruit and the carbonation lasted about 30 seconds after the tablet dissolved. Sometimes you'd drop in two tablets in the hope of actually getting some flavor out of it; that rarely worked. Occasionally, on a dare, a kid would put a tablet in his mouth to see what happened. I never did, but I suspect the result would have been similar to Zotz -- only 20-fold.
Part of it was probably due to one of the things the bragged about in their ads: Fizzies had no sugar. Instead, it used saccharine and cyclamates to flavor it. I would say the chemical taste was a turn off, but I really don't recall much taste at all.
Here is a look at a Fizzies ad, though the one I remember was an on-air plug by Shari Lewis who talked about a boy who had some Fizzies in his bathing suit. When he went swimming, it was the day Lake Michigan became superior. The pun was about as good as the drink.
Fizzies died out in the 70s as kids finally caught on, and were probably killed when cyclamates were banned. It seems to be available online, its sales fueled by nostalgia and selective memory. Still, there is something great about the concept of soda-in-a-pill, even if it never matched its expectations.
*The chemicals in Alka-Seltzer that cause the fizz are just baking soda and citric acid; the actual medicine has nothing to do with the carbonation.
**Cola was occasionally added as a flavor.
***At least, not the size shown on the commercials. Compare the size of the glass where the tablet is dropped (along with the fact that some of the bubbles are animated to make it seem more effervescent) with that the clown drinks from. Back then, of course, it was considered fair play to do anything in a commercial to make the product look better.