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Medhya rasayana are Ayurvedic drugs believed to promote intellect (medha), memory and other mental faculties. Charaka specifies four: the juice of Mandukaparni, powdered Yashtimadhu with milk, the juice of Guduchi, and a paste of Shankhapushpi. This review appraises the human clinical evidence for these four drugs and for two closely related plants, Brahmi and Ashwagandha, and examines how uncertainty about botanical identity affects interpretation. The best evidence concerns Bacopa monnieri. A meta-analysis of nine randomised trials found shorter Trail B and choice reaction times, and a systematic review of six 12-week trials found improvement in memory free recall but little effect in other domains. Classical scholarship, however, has argued that Brahmi and Mandukaparni are synonyms for Centella asiatica, and that Bacopa monnieri corresponds to a different classical plant, Aindri. For Centella asiatica, a meta-analysis of eleven trials found no significant benefit in any cognitive domain, only improved alertness and reduced anger. A placebo-controlled trial of Ashwagandha root extract in 50 adults with mild cognitive impairment reported better memory and executive function after eight weeks. For Yashtimadhu, Guduchi and Shankhapushpi, we found no randomised placebo-controlled trials of cognitive outcomes; Shankhapushpi has only open-label studies, and its name is applied to more than one plant. Most trials used standardised extracts rather than classical preparations, enrolled healthy volunteers, and lasted at most 12 weeks. We propose priorities for trials that test classical medhya preparations in defined populations, with authenticated plant material.