The commercialization of products derived from cannabis has to be done with the mandatory authorization and approval of the AEMPS - the Spanish Agency for Medicines and Health Products, who's mandate most closely meets this category of medicines; Currently there is a drug approved by this entity whose name is Sativex and has a 1: 1 ratio of CBD and THC.
In this link, of the AEMPS, you can consult its properties and main characteristics:
As you point out in your question, there is another possibility - although with other administrative obstacles - that would allow you to market it as a food supplement. In this case, the plant in question must be included in the list of varieties authorized by the European Union. These plants must have a THC content (the main psychoactive component of the plant) of less than 0.2%.
All the best,