Cough potion

A cough potion is presumably a potion which sooths and reduces coughing.

In 1996, Fred and George repackage their love potions as perfumes or Cough Potions to smuggle them into Hogwarts, as Filch had put a ban on all Weasleys' Wizard Wheezes products the previous year.

Appearances
Harry Potter and the Half-Blood Prince