Background: Hypertension is a major public health issue. With regard to the current trend, it has been estimated that one out of three people will be suffering from hypertension by 2025. This study was designed to provide a better insight into the adherence to treatment and its underlying reasons. Methods: A directed qualitative content analysis approach was conducted in collaboration with 35 hypertensive patients and 3 cardiologists in the form of in-depth interviews and focused group discussions from October 2015 to February 2016. Sampling was carried out from patients with hypertension using purposeful and heterogeneous method. Some of the PRECEDE model structures were applied as the conceptual framework. Results: The reasons affecting adherence to hypertension treatment were analyzed in three general categories of predisposing, enabling and reinforcing factors based on the model structures. Factors such as “knowledge”, “belief and attitude”, “mental-personality traits”, “culture and lifestyle” were classified as the predisposing factors category. “Access to health service” and “access to facilities in the workplace, home and society” were fit in the enabling factor category. The reinforcing factors category addresses “individuals’ internal incentives” and “family and health service providers’ support”.Conclusion: Several reasons account for non-adherence to treatment in hypertensive patients. Diversity of these reasons is an indication that design and implementation of different kinds of interventions are required in order to increase the patients’ awareness, empower them and encourage self-efficacy.