"PrEP reduces the risk of getting HIV from sex by about 99 percent when taken as prescribed. Although there is less information about how effective PrEP pills are among people who inject drugs, we know that PrEP pills reduce the risk of getting HIV by at least 74 percent when taken as prescribed," the CDC says.

A twice-yearly injection of Sunlenca (lenacapavir) reduces the risk of HIV infection by 96%, which is significantly more effective than oral pre-exposure prophylaxis (PrEP) using pills like Truvada, researchers report in the New England Journal of Medicine.

For oral medications that prevent new HIV infection to be effective, the patient must take certain actions, including attending doctor's visits every three months and—most importantly—consistency.