If marijuana was ever legalized would the gov control it and would they put chemicals and stuff in it like cigarettes?

Conspiracy theories aside - the 'Govt' does not produce cigarettes or put chemicals in the ones produced. Legal marijuana production and sale would be an entirely different situation to that of tobacco. For instance, its not illegal to grow tobacco for private consumption in this country, but its hard to grow and impractical for most people. If marijuana was similarly legal, most people would simply grow it themselves at home or buy from friends that are better gardeners.