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Background: Shodhana is the set of purification and processing procedures that Ayurveda prescribes before toxic plants (visha and upavisha dravyas), metals and minerals are used as medicines. It is widely claimed to remove or reduce toxicity, but the strength of the evidence varies greatly between materials. Objective: To review the physicochemical and toxicological evidence on how shodhana changes the composition and toxicity of poisonous plants, metals and minerals, and to identify what remains unproven. Methods: A critical narrative review of experimental studies that compared raw and processed material using chemical analysis, animal toxicity, cytotoxicity or mutagenicity assays, together with relevant classical and review literature. Results: For aconite, Strychnos nux-vomica, Croton tiglium and Abrus precatorius, processing in media such as cow's urine, milk, kanji and water consistently reduced marker toxic constituents or toxicity, although reductions were partial (for example, phorbol ester content fell by about 21–23% in Croton seeds) and the toxic principle was sometimes also the active one. For metals, shodhana by repeated heating and quenching altered surface structure, removed some trace elements, and increased brittleness, but did not lower the content of the principal metal; in lead, purity rose from 97.13% to 98.98%. Processing can also introduce new contaminants. Conclusion: Shodhana is best understood as controlled chemical transformation rather than as removal of the toxic element. Its effects are real but partial and material-specific, and need validated end-points and dose-linked toxicity data.