How often do I have to renew a Medical Marijuana Certificate in NJ? When the patient is seen for the first time by the doctor, the doctor will write an initial 30-day medical cannabis certification. This is to establish a relationshio with the patient. The patient is then reassessed after 30 days. The patient will then receive a 90-day certification, and be seen every 90 days (3 months) from then on. Patients are sent reminders to recertify by the New Jersey Medical Marijuana Program (NJMMP) every 60 days, so 30 days before expiry of the previous certification. It is best to recertify as soon as possible within this 30-day window, so as to ensure smooth transition month-to-month.