Background Effectiveness of anti-retroviral therapy (ART) requires strict adherence. Adherence ≥95% achieves optimum therapeutic levels and reduces drug resistance. We sought to determine factors associated with ART adherence within the context of patient demographics and factors, and explore care treatment and support strategies used by patients and health workers.

Methods A Mixed Method Sequential Explanatory Design (MMSED) was employed to study adult patients receiving ART from the University Teaching Hospital, Lusaka. Adherence was measured by missed clinic appointments and pharmacy collections over the last six months. The quantitative method assessed 715 complete pharmacy records extracted from the dispensing tool to ascertain demographic and patient factors. Bivariate and multivariate logistic regression analysis was employed. Qualitative research involved in-depth interviews with patients and key informants.

Results Results showed 79.4% of the patients were adherent to clinical appointments while 46.3% were adherent to pharmacy refills. Multivariate analysis showed lower adherence amongst the widowed on clinical appointments (OR=0.3; 95% CI: 0.1–0.9). The stepwise regression analysis revealed significant factors for adherence on clinical appointment and pharmacy refills for widowed, co-habiting and no education, (p=0.008, p=0.044, and p=0.018), respectively. About 80% of patients interviewed were adherent to ART.

Conclusions The results show moderate ART adherence (80%). However, in view of the identified factors affecting adherence, concerted and collaborative efforts through effective and efficient interventions are needed to improve the adherence levels to at least ≥95%.