National Institute of Mental Health (NIMH) | 559,642 followers on LinkedIn. The National Institute of Mental Health (NIMH) is the lead federal agency for research on mental disorders. | The National Institute of Mental Health (NIMH) is the lead federal agency for research on mental disorders. NIMH is one of the 27 Institutes and Centers that make up the National Institutes of Health (NIH), the nation’s medical research agency. NIH is part of the U.S.