We already have the cure for the common cold, see DDr. Linus Pauling "Vitamine C and the Common Cold". This guy was a double nobel prize winner, in a time when this meant something, so you better listen up. Vitamine C is most likely also effective against coronavirus. There exists a book about all this by Dr. Thomas E. Levy "Primal Panacea", I suggest you check out the reviews at Amazon. Medicine is not interested in cheap cures and never was, all they want is an expensive medicine which they can patent and sell.
Another substance which is most likely effective is Vitamine D.
And, probably, Iodine (Lugols Solution).