This Body Is Mine (1971)

Allen Meredith is a brilliant scientist but too mild-mannered to make an impact or fight for the money he needs. He has invented a process to exchange minds between bodies. His ambitious wife Ann persuades him to invite his boss, the domineering Jack Gregory, to their house for dinner. Once there, they drug him and Allen swaps bodies with Jack, then goes back to work to transfer millions into his account. But meanwhile Ann is finding the combination of Jack's masculine personality in Allen's body rather attractive and they begin making their own plans.