HELLO As you mentioned that your friend is having asthma ( allergic type ) with cough , from long time. In such type of cases usually pollen , mite , fine dusting powder, hay , fumes , smoking , sudden increase or decrease in temperature , pests (cockroaches ) pets ( animal like dog , cat ) are certain predisposing factors responsible for such type of symptoms , so avoidance play an important role in such cases. When such patient visit I prescribe them to take montelukast + bambuterol once or twice in day . Usually patient respond this treatment . Some patient feel fine tremors but drug adjust within 3-5 days . Hot coffee and steam inhalation also provide relief. Hope this will help your friend. Good luck.