Co-administration of traditional remedies and orthodox antimalarials in southwestern Nigeria: prevalence, demographic correlates, and implications for treatment policy

The efficacy of first-line artemisinin-based combination therapies (ACTs) in Nigeria is threatened by non-adherence to clinical guidelines. This includes the widespread use of traditional and herbal medicines (THMs) and discontinued monotherapies. This study aimed to quantify the prevalence of these practices, identify the populations most at-risk, and elucidate the treatment pathways involved to inform targeted public health interventions. A community-based cross-sectional survey was administered to 1500 adults in Osun State, Nigeria, using multi-stage sampling. Data on socio-demographics, treatment-seeking behaviour, and antimalarial/THM use were collected. Logistic regression analyses identified factors independently associated with THM use and high-risk practices. 40.7% of respondents reported using THMs for malaria. Their use was independently associated with age ≥ 30 years (aOR: 3.21, 95% CI 2.45–4.21), female gender (aOR: 1.68, 95% CI 1.30–2.17), education at secondary level or below (aOR: 7.45, 95% CI 5.89–9.42), and rural residence (aOR: 13.10, 95% CI 10.15–16.91). THM users were significantly more likely to initiate treatment through informal sources (54.9 vs. 3.4%, p < 0.001) and to report using chloroquine (57.4%) and injectable artemisinin monotherapies. Overall awareness of drug resistance (34.2%) and ACT completion importance (25.3%) was low. Critically, all antimalarial therapy must be preceded by parasitological confirmation, as treating undifferentiated febrile illnesses in high-transmission settings can exert sub-therapeutic selective pressure on concurrent asymptomatic parasitemia. The co-administration of THMs and non-recommended antimalarials is common and follows distinct demographic and behavioural patterns. These practices, facilitated by informal treatment channels and low therapeutic literacy, represent a clear deviation from national policy and threaten ACT effectiveness. The findings provide an evidence base for the Nigerian Malaria Elimination Programme to design community-specific interventions, including vendor regulation and education campaigns targeting high-risk groups.