A deep penetrating cough medicine that provides fast soothing relief from chesty coughs, allowing you to get on with your day. Benylin chesty cough original contains diphenhydramine hydrochloride an expectorant to help to loosen and expel mucus. Levomenthol helps to ease congestion and relieve stuffy noses.even after your cold or flu has gone, sometimes a cough can persist for quite some time afterwards. This can be truly debilitating, uncomfortable and can affect your daily life. By using a benylin cough syrup, the symptoms of a mucus, chesty or dry cough can be instantly soothed and relieved.who can take benylin adults should take two 5ml doses four times a day. Children aged 6 12 years and over should take one 5ml spoonful four times a day. Not recommended for children under 6 years old.