Men who have sex with men (MSM) continue to be disproportionately affected by HIV. The majority of HIV infections among MSM occur through exposure to the rectal mucosa during receptive anal intercourse (RAI). During RAI, many MSM will use lubricants, which can potentially cause mucosal inflammation and damage. A new HIV prevention intervention, called pre-exposure prophylaxis (PrEP), recommends that MSM at risk of HIV infection take a daily anti-HIV medication called Truvada (tenofovir/emtricitabine) which is highly effective. However, it is not known if the use of lubricant during RAI will interfere with the efficacy of PrEP for HIV prevention.