Suppose someday it is enacted a law saying something like "The use of chemical substances, natural or artificial, when used for recreational purposes, it is authorized" or "will not be criminally persecuted". Can such a law exist without the another law explicitly allowing the production of such chemical substances?
Yes it can. That already has been the case in Washington state.
Initiative 502 legalizes the possession of marijuana and marijuana-enhanced produpcts and ultimately their manufacture and sale. As of Dec. 6, 2012, when I-502 becomes effective, persons 21 years of age or older will be able to possess up to an ounce of marijuana for personal use in private settings.
However, the State Liquor Control Board has until December 2013 to establish a licensing system for the manufacture and sale of marijuana; this system must be in place before people may legally manufacture and sell marijuana.
In addition to its applicability in regards to drugs, it should be understood that the 18th Amendment to the United States Constitution worked in precisely this way. To with, the 18th prohibited:
the manufacture, sale, or transportation of intoxicating liquors within, the importation thereof into, or the exportation thereof from the United States
Note what is missing - there was never a prohibition on the consumption of or use of alcohol. As such, technically it was completely legal to drink - just not to make, transport, or buy alcohol.