It was not until the mid-1990s that researchers saw another way: An enzyme called dipeptidyl peptidase four (DPP4) broke down GLP, and by inhibiting it, researchers could boost GLP levels in the body.

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In 1995 he and colleague Carolyn Deacon proved that the obscure dipeptidyl peptidase enzyme was the main culprit and in a paper published in the journal Diabetes suggested that drugs that blocked this enzyme would make good treatments.

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