Why is the only translation for “medicine”, “médicaments” (plural) leading one to believe that this might be one of those situations where the plural is required? Perhaps the “s”needs to be removed.
Hints have been fixed, thank you!
Is "agir" used for other things not working - like people or solutions - or is it only used like this with medicine?
"Le médicament n'est pas efficace" devrait être accepté ?