A canister for a metered dose inhaler has high and low pressure chambers for a propellant and for an inhalable drug and vaporised propellant. The low pressure chamber has an opening for a metering valve. A pressure regulating valve is between the high and low pressure chambers and provides a flow path from them. A metering valve dispenses a metered dose. The valve includes a metering valve body having a propellant metering chamber with a propellant inlet and a product metering chamber with a product inlet, and a metering valve stem with a dispensing nozzle, a propellant inlet plug and a product inlet plug. The metering valve stem moves to a dispensing position. In the dispensing position, the propellant and product metering chambers are in fluid communication with atmosphere via the dispensing nozzle of the metering valve stem such that a metered dose of product and propellant can be dispensed.
