Inhaled therapy is essential for the treatment of asthma and chronic obstructive pulmonary disease (COPD). There are two main types of inhalers for the delivery of respiratory drugs: the metered dose inhaler (MDI), which uses HFCs as the propellant and the dry powder inhaler (DPI). The choice of the most suitable inhaler is a complex decision taken between doctor and patient. A minority of patients (10-20 per cent or less), notably the very young and very old, cannot use available alternatives to HFC MDIs. These patients generally cannot use dry powder inhalers. This is because a strong breath is needed to inhale the drug within the inhaler.