Following drugs are used as analgesics. One among them is different from others. Identify it and state the reason. Morphine, Heroin, Aspirin, Codeine.

morphine-Morphine is anopioidanalgesicdrug, and the main psychoactive chemical inopium. In clinical medicine, morphine is regarded as the gold standard of analgesics used to relieve intense pain morphine acts directly on thecentral nervous system(CNS) to relievepain.
heroin-it is anopioidanalgesicoriginally synthesized byC.R. Alder Wrightin 1874 by adding twoacetylgroups to themoleculemorphine, which is found naturally in theopium poppy. It is the 3,6-diacetylesterof morphine. Heroin itself is an inactive drug, but when inserted into the body, it converts intomorphin
aspirin-Aspiri also known asacetylsalicylic acid is asalicylatedrug, often used as ananalgesicto relieve minor aches and pains, as anantipyreticto reduce fever, and as ananti-inflammatorymedication.
codeine-codeineor3-methylmorphine(a naturally occurring methylatedmorphine) is anopiateused for itsanalgesic,antitussive,antidiarrheal,antihypertensive,anxiolytic,antidepressant,sedativeandhypnoticproperties.