Is a contraceptive injection safe in an 18-year-old and what tests should be done before?

As I understand it, you mean Depo-Provera. If so, please read on. It is not recommended to use the drug Depo-Provera before the onset of the first menstruation. In adolescents between 12 and 18 years of age, the use of the preparation is associated with a statistically significant reduction in the bone mineral density index. In adult women, regardless of whether they are younger or older, it is believed that safety and efficacy are the same. The choice of contraceptive method is decided by the gynecologist in cooperation with the patient. Age is not the only factor that is taken into account. I enclose information that may be of interest to you: https://www.gdziepolek.pl/produkty/21949/depo-provera-iniekcja/apteki You can read about the research related to the use of contraception here: