Full Spectrum Cannabis Oil – 1g What is FSO? · A darker colored liquid concentrate made by soaking cannabis plants in a solvent. · During the solvent removal process, the oil undergoes decarboxylation. This means that the THCa is converted into THC and can produce a psychoactive effect. · Concentrates all of the elements in the cannabis plant, not just THC and terpenes. · The purpose of a full spectrum cannabis extraction is to concentrate as many of the compounds as possible, not just THC, usually resulting in a darker colored product.