Frequently asked questions How much medical marijuana am I allowed to possess in California with a Medical Marijuana Certificate? In California, there is no express limit on the amount of medical marijuana a patient can possess. However, there may be legal implications should a patient possess an amount indicative of selling or trafficking. Leafwell recommends you speak with an attorney if you may have a need to possess medical marijuana in a quantity greater than an amount reasonable for personal, daily consumption. The generally accepted, non-official limit for medical marijuana patients is 8 ounces on their person, or up to 60 grams of cannabis concentrate (1 oz. being equivalent to 8 grams).