This study examines the influence of Instagram influencer credibility on menstrual product purchase intention among female consumers in Southeast Nigeria. Despite the rapid growth of influencer marketing within Nigeria’s digital economy, limited empirical research has examined its impact on health-related consumer behaviour in culturally sensitive domains such as menstrual hygiene. Grounded in Source Credibility Theory and the Consumer Online Brand-Related Activities (COBRA) framework, the study investigates how perceived influencer credibility shapes consumer engagement and purchasing decisions. The survey method was adopted. Quantitative data were collected from 420 female Instagram users across the five Southeast Nigerian states namely Abia, Anambra, Ebonyi, Enugu, and Imo, while qualitative insights were obtained through focus group discussions and in-depth interviews. Data were analysed using descriptive statistics, regression analysis, and thematic analysis. The findings indicate that perceived Instagram influencer credibility significantly predicts menstrual product purchase intention. Influencer authenticity, cultural relatability, and experiential communication were found to enhance trust and emotional connection with brands, although affordability and persistent cultural norms moderate long-term loyalty. The study contributes to influencer marketing and health communication scholarship by demonstrating how credibility-driven digital engagement shapes consumer behaviour within culturally sensitive contexts in emerging markets. It highlights the role of Instagram influencers as both marketing agents and facilitators of menstrual health awareness.