Blondie Knows Best (1946)

Dagwood is about to get sued by a neighbor for $500,000 and needs to raise some money real fast as he only makes about $4,000 a year working for the J. C. Dithers Construction Company. He finally obtains the money by allowing himself to be the guinea pig injected with a new truth serum. As a result of being able to speak only the truth, which he always did anyway, he wins a new contract for the Dithers firm and a raise.