A 7-day wait after a Depo shot is usually needed when it is your first shot or when the shot is given late or outside the early days of your period. During this time, the medicine may not yet be giving reliable pregnancy protection, so a backup method is needed.
Depo works by using medroxyprogesterone to prevent ovulation and make pregnancy less likely. When the shot is given within the first few days of a period, protection may start right away because pregnancy is unlikely and ovulation has not occurred. If it is given later, the body may need several days for hormone levels to become reliably protective.
During those 7 days, use condoms or avoid sex if you do not want to get pregnant. The same advice may apply if a repeat shot is late, especially if more than the recommended time has passed since the last injection.
Do not rely on Depo alone during the waiting period unless a healthcare professional tells you it is safe. Speak with an OB-GYN, primary care clinician, pharmacist, or family planning clinic if you are unsure about timing or missed shots.