Abstract
Plants produce an extensive repertoire of secondary metabolites, developed over evolutionary time to support survival. Among these, D-limonene, a monoterpene exuded by citrus fruits, has demonstrated a broad range of pharmacological activities. This review elucidates limonene's biological versatility, spanning antioxidant, anti-inflammatory, antitumor, antidiabetic, neuroprotective, and gastroprotective domains. Synthesizing data from both preclinical and early-phase clinical research, we explore its molecular mechanisms, ranging from reactive oxygen species mitigation and apoptosis induction to metabolic remodeling and neurotransmitter modulation. Special attention is given to limonene's emerging role in oncological therapeutics, notably in breast and liver cancers, and its capacity to ameliorate pathophysiological hallmarks of diabetes and neurodegeneration. Its low toxicity and high bioavailability support its potential as a safe adjunct or alternative in phytotherapy. This review advocates for continued investigation into limonene's translational potential across a spectrum of neoplastic and non-neoplastic diseases.