Neuroprotective Effects and Mechanisms of Carvacrol and Thymol in Alzheimer's Disease: A Scoping Review.

Background/Objectives: Alzheimer's disease (AD) is a multifactorial neurodegenerative condition characterised by cognitive impairment, cholinergic deficiency and neuroinflammation. Carvacrol and thymol are two related natural monoterpenes with reported antioxidant, anti-inflammatory, anti-apoptotic and cholinesterase-inhibiting properties. This scoping review aims to map the current evidence regarding the effects of carvacrol and thymol on AD-related pathologies and identify their mechanisms of action. Methods: A systematic literature search was conducted in February 2026 across PubMed, Scopus and Web of Science. This review included original, English-language primary research articles investigating the effects of carvacrol and thymol on AD using in vitro, in vivo, or in silico models. Results: From an initial pool of 87 unique records, 30 primary studies met the inclusion criteria, encompassing direct AD pathology models (e.g., amyloid-beta), AD-associated risk models (e.g., metabolic or hypertensive impairment), and general cognitive impairment models. Both carvacrol and thymol reduced escape latency during spatial learning acquisition training and increased time spent in the target quadrant during probe trials, indicating improvements in both learning and memory retention, although several studies reported non-linear relationships. At the cellular level, carvacrol and thymol modulated distinct redox and inflammatory pathways, including nuclear factor erythroid 2-related factor 2 upregulation and tumour necrosis factor-alpha suppression. Synthetic derivatives and nanocarrier formulations (e.g., liposomes, nanoemulsions) demonstrated enhanced acetylcholinesterase inhibition and biological stability relative to parent monoterpenes. No clinical trials were identified, and formal critical appraisal was not performed. Conclusions: Preclinical evidence indicates that carvacrol and thymol show potential multi-targeted neuroprotective activity across diverse models of cognitive dysfunction. However, clinical translation remains unproven due to heterogeneous experimental designs, pharmacokinetic limitations, a lack of human trials, and unassessed study quality.