There isn’t a specific limit on how many times you can visit Missouri dispensaries. Instead, there’s a limit on how much product you can purchase. Missouri marijuana laws state that cardholders can buy up to four ounces of dried, unprocessed cannabis — or its equivalent — within a 30-day period.   Some patients may require more cannabis for their medical conditions. If this is the case, you must have two different physician certifications that state how much cannabis you need each month.