Tuōyǎng máhuángjiǎn shì yī zhǒng qiángliè de xīngfènjì.
Methamphetamine is a powerful stimulant.
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Literally 'deoxy + ephedrine': 脱氧 = 'deoxy' (脱 remove + 氧 oxygen), 麻黄碱 = 'ephedrine' (the alkaloid 碱 from the 麻黄 ephedra plant). The chemical name reflects exactly what it is - a deoxygenated form of ephedrine.
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This is the formal pharmacological name. In news and street language you'll more often see 冰毒 ('ice drug') or 甲基苯丙胺 ('methamphetamine' - the IUPAC-style name).