This study was conducted to investigate the effect of loneliness and perceived social support on medication adherence self-efficacy in hypertensive patients. This descriptive cross-sectional study was conducted between March and June 2015 at 5 Family Health Centers in central Erzincan in eastern Turkey. The data were collected through face-to-face interviews using a descriptive questionnaire, the UCLA Loneliness Scale, the Multidimensional Scale of Perceived Social Support, and the Medication Adherence Self-Efficacy Scale Short Form. The mean score obtained from the UCLA Loneliness Scale was 38.35 +/- 9.85, from the Multidimensional Scale of Perceived Social Support 64.10 +/- 18.31, and from the Medication Adherence Self-Efficacy Scale 40.27 +/- 11.97. The mean UCLA Loneliness Scale score was found to have a low negative correlation with the mean Medication Adherence Self-Efficacy Scale score and a highly significant negative correlation with the mean Multidimensional Scale of Perceived Social Support score (P < .001). There was also a very low positive significant correlation between the mean scores of the Multidimensional Scale of Perceived Social Support and the Medication Adherence Self-Efficacy Scale (P < .001). This study revealed that individuals with hypertension perceived a moderate level of loneliness, and their perceived social support and medication adherence self-efficacy were higher than the moderate level. Perceived loneliness and perceived social support were significant indicators of perceived medication adherence self-efficacy. Therefore, effective consultancy services should be provided to hypertensive patients to increase their social support and to make positive changes in their perceived loneliness so that their perceived medication adherence self-efficacy can be improved. (C) 2020 Society for Vascular Nursing. Published by Elsevier Inc. All rights reserved.