<p>Nowadays, addressing insect pest infestation effectively requires environmentally sound and sustainable pest control methods that minimize environmental pollution. Caffeine (1, 3, 7-trimethylxanthine), a plant-derived secondary metabolite, has insecticidal, hormonal and antifeedant properties, making it a promising and more sustainable alternative for pest management. In this study, the red flour beetle <i>Tribolium castaneum</i> Herbst (Coleoptera: Tenebrionidae), a serious stored pest, was used to investigate the effects of different caffeine concentrations on life-history traits. We applied two delivery methods: 1) oral exposure through a caffeine–sucrose solution for adults, and 2) dietary incorporation of caffeine powder mixed with wheat flour and brewer’s yeast for adults and their larvae. To evaluate the effect of caffeine on life-history traits, adult longevity, pupation rate, larval period, pupal weight, adult body size and food consumption were examined. Results revealed higher caffeine concentrations (&gt; 1%) significantly reduced longevity, delayed pupation, decreased pupal number, pupal weight and adult body size in both males and females. Lower caffeine concentration (0.01%) increased pupal number but resulted in lower offspring quality, such as smaller pupal weight and adult size. The results show that caffeine has negative effects on life-history traits of <i>T. castaneum</i>, suggesting its potential use as a natural pesticide in caffeine-based sustainable pest-management programs and integrated pest management (IPM).</p>