What characteristic primarily differentiates a medication designed for contraceptive use?

A medication designed for contraceptive use is primarily intended to prevent pregnancy. This is the fundamental purpose of contraceptives, which can include various forms such as pills, injections, implants, and devices. These medications work by interfering with the normal reproductive process, either by preventing ovulation, fertilization, or implantation of an embryo.

The other options do not align with the primary purpose of contraceptives. While some medications may provide pain relief, that is not a characteristic of contraceptive drugs. Additionally, while some contraceptives are injected, many effective options are available in oral, topical, or intrauterine forms, making injection not a requisite characteristic. Lastly, medications specifically designed to be used during illness do not hold relevance to contraceptive use, as contraceptives are utilized continuously or based on a specific reproductive cycle rather than strictly during health crises.