In sub-Saharan Africa, harmful alcohol use among male drinkers is high and has deleterious consequences on adherence to antiretroviral therapy (ART), HIV clinical outcomes, and couple relationship dynamics. We conducted in-depth qualitative interviews with 25 Malawian couples on ART to understand how relationships influence adherence to ART, in which alcohol use emerged as a major theme. Almost half of men (40%) reported current or past alcohol use. Although alcohol use was linked to men's non-adherence, women buffered this harm by encouraging husbands to reduce alcohol use and by offering adherence support when men were drinking. Men's drinking interfered with being an effective treatment guardian for wives on ART and also weakened couple support systems needed for adherence. Relationship challenges including food insecurity, intimate partner violence, and extramarital relationships appeared to exacerbate the negative consequences of alcohol use on ART adherence. In this setting, alcohol may be best understood as a couple-level issue. Alcohol interventions for people living with HIV should consider approaches that jointly engage both partners.