Haha! Who says that!? Psychoactive resins are long strings of hydrocarbons. To assemble them, you have to have plenty of carbon available, from the soil (molasses and other sources) and atmosphere (CO2). Atmospheric CO2 is usually plenty, and you don't HAVE to add a sugar supplement to your feeding, but enrichment of the air or water with available carbon is a technique to increase both bulk and amount of resin produced!
Yay, carbon.

Don't forget it's useless if you have other problems in the grow.