Additional Study Information: PrEP (Pre-Exposure Prophylaxis) is medication that is taken to prevent HIV if a person is exposed to HIV. Research is ongoing to develop PrEP medications that may be both convenient and effective. This study is important because people who inject drugs face multiple overlapping individual, social, legal, and structural challenges contributing to a disproportionate HIV burden and negative health outcomes. The purpose of Purpose 4 is to observe how an investigational long-acting injectable HIV prevention medication, Lenacapavir (LEN) moves throughout the body in people who inject drugs, in the U.S. and how they feel receiving an injection every 26 weeks versus taking F/TDF, also known as Truvada, pills daily. There are 2 phases to this study. In the first phase, which lasts one year, you will be randomly assigned to one of two groups: the group that receives LEN or the group that receives Truvada. You will not get to pick which group you are in or which medication you will receive. If assigned to the LEN group, you will receive two injections on day 1 and two injections again 26 weeks later. There is a chance the injection will leave a bump under the skin. If assigned to the Truvada group, you will take the tablets by mouth once a day. In the second phase (for up to 1.5 years), every participant will take Truvada by mouth once a day regardless of which group they were in for the first year. The first phase is 52 weeks long and the second phase is an additional 78 weeks making the total length of time for this study approximately 2.5 years. There are at least 13 scheduled visits. Visit procedures include, but are not limited to, a total of four injections if assigned to the LEN group, questionnaires about sexual behaviors, intimate partner violence, family planning as well as physical exams. You will have blood drawn for HIV testing and give urine specimens to test for sexually transmitted infections and pregnancy. You will be compensated for your time and travel.