A Systematic Literature Review of Hallucinations in Large Language Models

This review systematically maps research on hallucinations in large language models using a descriptive scheme that links model outputs to four system architectures: unaugmented generation, post-hoc reactive validation, proactive detection-and-mitigation, and fully integrated detection-and-mitigation designs. Our methodology for this systematic review follows the PRISMA guidelines to ensure transparency and reproducibility. We searched IEEE Xplore, ACM Digital Library, and ScienceDirect for studies published between 2015 and January 2025 and extracted 125 peer-reviewed papers across nine application domains. Quantitative analysis shows that question answering and multimodal tasks account for 48% of all papers, whereas software engineering, educational technology, and autonomous systems are underexplored. Although 87.5% of the studies rely on additional reactive or proactive defenses, only 8.8% implement integrated architecture-level safeguards, revealing a critical gap in unified and dynamic architectures. The resulting classification matrix and domain map provide a diagnostic tool for locating blind spots and comparing architectural maturity. Three actionable priorities emerge: develop integrated reasoning-and-verification loops that pre-empt hallucinations; transfer proven causal-intervention and multi-agent validation pipelines to high-stakes, under-represented domains and benchmark them under real conditions; and build modular, cross-domain evaluation frameworks that isolate the contribution of individual mitigation components and support ablation studies. By consolidating fragmented evidence and quantifying architecture-domain imbalances, this review establishes a traceable foundation for engineering reliable, explainable, and domain-adaptable countermeasures to hallucinations in generative language technology.