linctus
A linctus is a thick, syrupy cough medicine that you sip slowly and let trickle down the back of your throat rather than gulp. The whole point is the lingering coating it leaves behind, so the soothing happens locally before the drug is even swallowed.
Formally, a linctus is a viscous, sweet oral liquid intended to be taken in small amounts without dilution, so that it bathes and demulces (soothes) an inflamed or irritated throat. The high sugar or syrup base gives it the cling and viscosity that prolong contact, and it often carries a cough suppressant such as codeine or a demulcent and flavouring.
Because the soothing effect depends on direct contact, a linctus should be sipped undiluted and not washed down with water immediately afterward. It is a niche oral liquid: useful for cough and sore throat, but not a general vehicle for systemic drugs the way a syrup or solution is.
Simple Linctus BP is a viscous citric-acid-and-syrup preparation sipped to soothe a dry, tickly cough through its demulcent coating action.
A clinging, viscous liquid coats and soothes the throat where it lingers.
Telling the patient how to take it matters as much as the formula: a linctus sipped slowly works locally, but the same liquid washed down with water loses its soothing effect.