Asthma and COPD can sometimes behave as very similar respiratory conditions. They both affect the small airways of the lungs (bronchioles) and therefore the symptoms can be the same: cough, wheeze, chest tightness, breathlessness etc.
Asthma is an inflammatory condition of the airways, and this inflammation causes the airway to sometimes suddenly constrict (narrow) causing asthma attacks. These flare-ups can happen suddenly in response to certain triggers. The symptoms of asthma can also be very variable from day to day.
COPD (chronic obstructive pulmonary disease) is a condition that usually occurs later in life and in most patients there is a history of smoking for many years or exposures to dusts, fumes etc. COPD also affects the airways, but the obstruction (narrowing) of the airways is less variable. Therefore, respiratory symptoms in COPD are less variable day-to-day.
Treatments for both asthma and COPD are based on inhalers. There are many types of inhalers, however most patients these days are given a combination inhaler which contains two or three different medications in the same device. Most contain a corticosteroid (which treats inflammation) and one or two bronchodilators (medications which open up the airways). As most inhalers have similar types of medication, sometimes they have good effects in both asthma and COPD (even if the conditions are different).
It can be frustrating for patients if their doctors do not agree on the diagnosis (i.e. one doctor says it is COPD another says it is asthma, or the same doctor changes the diagnosis at some point). This is sometimes expected as there can be considerable overlap between the two conditions.