Symbicort is an inhaler which in the case of asthma can be used as both a controller and a reliever. This is because one of the medications contained in Symbicort, called formoterol, has a quick onset of action, usually 5-10 minutes. Formoterol acts as a bronchodilator – a medication which opens up the small airways to help you breathe better.
However, Symbicort also contains another medication called budesonide which is a corticosteroid. This acts as an anti-inflammatory medication which helps control inflammation in the airways in the long term (hence why it is called controller medication). These two medications work together synergistically in the case of asthma.