 [ Symptoms ] how long does it take for depo provera to take full effect  i did ask the question but was lead to everywhere but the answer how does that help anyone who needs the true answer i did receive my injection after my last menstrual cycle how would i figure out when i will be protected with the smallest chance of getting pregnant it has been 22 years since i was last on birth control but we just can not take the chance of my getting pregnant at this time in our lives [ Disease ] hi if taken within 5 days of your last period straight away but have you looked up about the side effects of depo shotprovera if i was you give it a good read just google depo provera side effects its all there reason you may not want to stay on it after reading about the side effects good luck