1. A process for producing an extract containing tetrahydrocannabinol, cannabidiol and optionally the carboxylic acids thereof from Cannabis plant material, wherein the dried plant material is comminuted, characterized in that said plant material is extracted by means of CO2 under supercritical pressure and temperature conditions at a temperature in a range of approx. 31 degree C to 80 degree C and at a pressure in a range of approx. 75 bar or 500 bar, or is extracted in the subcritical range at a temperature of approx. 20 degree C to 30 degree C and a supercritical pressure of approx. 100 bar to 350 bar; or is extracted under subcritical pressure and temperature conditions; and the obtained primary extract is separated out under subcritical conditions or under conditions subcritical in terms of pressure and supercritical in terms of temperature. 2. The process according to claim 1, characterized in that plant material of Cannabis sativa L., in particular hemp of the fiber type and/or hemp of the drug type, is employed as cannabis plant material. 3. The process according to claim 1 or 2, characterized in that to the CO2 an entraining agent is added which is selected from the group comprised of: propane, butane, ethanol, and water. 4. The process according to any one of claims 1 to 3, characterized in that in the supercritical range a temperature of approx. 45 degree C to approx. 65 degree C and a pressure of approx. 100 bar to 350 bar, preferably a temperature of approx. 60 degree C and a pressure of approx. 250 bar, are used. 5. The process according to any one of claims 1 to 4, characterized in that an adsorbent is arranged on the material to be extracted downstream in terms of the CO2 flow. 6. The process according to claim 5, characterized in that the adsorbent is selected from the group comprised of: silica gel, diatomaceous earth, bentonites, bleaching earth, activated carbons, in particular magnesium oxide and alumina, as well as mixtures thereof. 7. The process according to any one of claims 1 to 6, characterized in that extraction is repeated at least once, with extraction preferably being repeated with diatomaceous earth and/or another adsorbent. 8. A primary extract from cannabis plant material, containing tetrahydrocannabinol and cannabidiol and optionally the carboxylic acids thereof, characterized in that it may be obtained through a process in accordance with any one of claims 1 to 7; and in that it contains at least reduced proportions of monoterpene and sesquiterpene hydrocarbons, alkaloids, flavonoids and chlorophylls. 9. A primary extract according to claim 8, characterized in that tetrahydrocannabinol includes at least Delta<9>-tetrahydrocannabinol and/or Delta<8>-tetrahydrocannabinol and/or the carboxylic acids thereof. 10. A primary extract according to claim 8 or 9, characterized in that tetrahydrocannabinol and/or the carboxylic acids thereof are the main constituent if a hemp of the drug type is used as a starting material. 11. A primary extract according to any one of claims 8 to 10, characterized in that cannabidiol and/or the carboxylic acids thereof are the main constituent if a hemp of the fiber type is used as a starting material. 12. A primary extract according to any one of claims 8 to 11, characterized in that it is dissolved in ethanol, separated from waxes not soluble therein, and the solvent is again removed under reduced pressure. 13. A process for producing tetrahydrocannabinol from the primary extract in accordance with any one of claims 8 to 12, characterized in that in the primary extract cannabidiolic acid and tetrahydrocannabidiolic acid are decarboxylated into cannabidiol and tetrahydrocannabinol through increase in temperature; the decarboxylated primary extract is dissolved in the CO2 extracting agent used, and in this condition is treated by means of a high-pressure vessel charged with a catalyst for anellation of cannabidiol into tetrahydrocannabinol and a water-binding agent, wherein cannabidiol is reacted to give tetrahydrocannabinol; and the product enriched in tetrahydrocannabinol is separated at pressure and temperature conditions subcritical for CO2. 14. A process for producing cannabidiol from the primary extract in accordance with any one of claims 8 to 12, characterized in that in the primary extract cannabidiolic acid and tetrahydrocannabidiolic acid are decarboxylated into cannabidiol and tetrahydrocannabinol through increase in temperature; and subsequently the cannabidiol is separated through column chromatography on silica gel or preparative high-pressure liquid chromatography.