Covonia Night Time Formula 150ml Dextromethorphan Hydrobromide. Diphenhydramine Hydrochloride. Calms & controls troublesome coughs & so aids restful sleep. DRY NIGHT TIME COUGHS. ONLY FOR USE AT NIGHT TIME. An oral solution for the night time symptomatic relief of non-productive coughs & congestive symptoms associated with colds. Action. Covonia Night Time Formula contains dextromethorphan hydrobromide which acts to reduce your desire to cough & diphenhydramine hydrochloride (an antihistamine) which helps dry up your runny nose & relieve nasal congestion.