Stevia is a plant originally from South America. Its leaves have a substance which is very sweet. Because of this sweetness the plant is also called sweet herb. In South America it is used to sweet meals and drinks like tea.
In the EU it was long time not allowed to use it, because it was not sure if the substances from the plant are mutagenic. In various studies it could be demonstrated that the substance «Stevioside» which is the part of the plant that sweets meals, is not dangerous for us human beeings. But the metabolite of Stevioside the Steviol had caused some problems in animal experiments.
In 2011 the Steviosid had been accepted from the European High Commission as a food aditive. In 2012 the Belgian chocolate company Cavalier together with Barry Callebaut launched the first chocolate sweetened by Stevioside. To make a chocolate without sugar it is needed to change the recipe totally, because the sugar in the chocolate does not only have the function to sweet the chocolate, as well it is needed technologically. How these two companies did it is not known, but by now different companies produce chocolate made with stevioside instead of sugar to decrease the calories in chocolate.
It can be a good way to make chocolate less unhealthy but people who have tested this chocolate said that the taste is very different.
Try it and do your own assessment!