 Other 5-HT4 receptor agonists have shown potential to be nootropic and antidepressant drugs, but have not been marketed for such indications.Valerenic acid, a constituent of valerian root, has been found to act as a 5-HT5A receptor agonist, and this action could be involved in the sleep-promoting effects of valerian.No selective agonists of the 5-HT6 receptor have been approved for medical use.