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Correct identification of a drug is the first requirement of Dravyaguna, and classical texts already recognise disputed (sandigdha) drugs and permitted substitutes (pratinidhi). In modern trade, raw drugs are sold as dried roots, barks, stems and powders that cannot easily be identified by appearance, and deliberate or accidental substitution is common. DNA barcoding identifies species from short standard DNA sequences and can work on fragmented or powdered material. This review summarises DNA-based evidence of adulteration in Indian herbal trade, the barcode regions in use, methodological limits, and integration with pharmacopoeial standards. A global analysis of 206 DNA-based studies covering 5,957 products found 27% adulterated, with 31% of 752 products from India. In raw drug markets in South India, 12% of 203 samples of 30 species were adulterated, with substitution ranging from 20% to 100% by species; all samples sold as Sida cordifolia were Sida acuta. In 93 finished products from Coimbatore, about 60% contained species not on the label. Barcoding has also resolved confusions between Tinospora species, between Bacopa monnieri and Centella asiatica, and among plants sold as Bala. Its limits are real: DNA is degraded or absent in extracts, oils and processed formulations, public sequence databases contain unvouchered errors, and barcoding detects identity rather than quality or potency. We recommend a vouchered national reference library for pharmacopoeial species, barcoding of raw drugs at procurement, and combined DNA and chemical methods for finished products.