How to start using DMPA Starting DMPA for the first time requires an assessment by a doctor and a prescription. This assessment enables you to ask any questions you may have and to be certain that it is the most suitable method for you. The first injection of DMPA is usually given during the first five days of a period. In some cases condoms will need to be used for seven days after the first injection. It is very important that there is no chance of an early pregnancy at the time of injection as this may lead to a delay in the diagnosis of a pregnancy.