Background/Objectives: Male hypogonadism affects 35-50% of men with type 2 diabetes mellitus (T2DM) and obesity. The relationship between testosterone deficiency and response to incretin-based therapies (GLP-1 and GIP receptor agonists) remains incompletely understood. This systematic literature review, conducted following PRISMA 2020 guidelines, examines whether male hypogonadism represents a risk factor for poor response to incretin therapy or, conversely, whether these agents offer therapeutic benefits for this population. Methods: A comprehensive systematic literature search was conducted on 31 December 2024, across PubMed/MEDLINE, Scopus, and Web of Science using three search domains: (1) hypogonadism and incretin therapy response; (2) testosterone deficiency and GLP-1/GIP receptor agonists; (3) incretin response and testosterone. Eligibility criteria included human studies (randomized controlled trials [RCTs], observational studies, cohort studies, cross-sectional studies, systematic reviews, and meta-analyses) in adult men reporting testosterone levels and/or incretin response. Animal studies, pediatric populations, case reports with n < 5, editorials, and letters without data were excluded. Study selection followed PRISMA 2020 guidelines with independent dual screening. Risk of bias was assessed using the Cochrane Risk-of-Bias 2.0 tool (ROB2) for RCTs, the Newcastle-Ottawa Scale (NOS) for observational studies, and AMSTAR-2 for systematic reviews and meta-analyses. Due to substantial heterogeneity in study designs, populations, interventions, and outcome measures, a meta-analysis was not feasible; therefore, a narrative synthesis was performed. Results: From 326 records identified, 29 studies were included after deduplication and screening (primary studies: 14; systematic reviews/meta-analyses: five; narrative reviews/expert opinion: 10). Risk-of-bias assessment revealed moderate-to-high overall risk: RCTs had small sample sizes (n = 12-42) and short follow-up (12-24 weeks), raising concerns about statistical power; observational studies were of fair-to-good quality (NOS 4-7 stars) but subject to confounding; and systematic reviews were of low-to-moderate confidence (AMSTAR-2). Primary evidence from RCTs and observational studies demonstrates that GLP-1 receptor agonists (GLP-1RAs)-particularly semaglutide and liraglutide-and the dual GIP/GLP-1 receptor agonist tirzepatide significantly increase total testosterone levels in men with obesity-related functional hypogonadism (mean increase 2.5-5.2 nmol/L). This effect is largely mediated by weight loss and improvement of insulin resistance rather than direct androgenic action. Evidence regarding whether baseline hypogonadism impairs glycemic or weight-loss response to incretin therapy is limited and indirect; no adequately powered comparative trials stratified by baseline testosterone status were identified. Conclusions: Incretin-based therapies, particularly GLP-1 receptor agonists and the dual GIP/GLP-1 receptor agonist tirzepatide, appear to improve testosterone levels in men with obesity-related functional hypogonadism, an effect that is largely mediated by weight loss and improvement of insulin resistance rather than a direct androgenic action. However, direct comparative evidence between hypogonadal and eugonadal men regarding glycemic or weight-loss response to incretin therapy remains insufficient to draw firm conclusions. The hypothesis that male hypogonadism does not impair incretin therapy response is biologically plausible but is currently supported only by indirect evidence. Prospective, adequately powered trials stratified by baseline testosterone status are needed to resolve this question.
