Abstract: An accessory for an inhaler unit may be retrofit into a conventional nebulizer system having a manifold or an inlet air tube. The accessory includes a one-way air valve that closes except when air is being inhaled. The one-way valve closes to prevent exhaled air/gas from flowing through the manifold and inlet air tube and out to the surrounding atmosphere. Thus, exhaled air/gas does not flow out of the system and does not carry medicine with it, greatly reducing medicine waste. Because the preferred inhaler system does not include any exhale/exhaust valve or any other outlet for exhaled air/gas, the user may loosen his lips, for example, to exhale. The accessory may be provided simply as a single one-way valve retrofit into an existing air tube of a conventional nebulizer system, as an air tube-valve combination that may be attached to a nebulizer system manifold, or as original equipment manufacture (OEM) for a nebulizer system.