An atomizing nebulizer for dispensing a substance or medicament is described. The nebulizer is formed with a reservoir base releasably secured to an effluent vent cap that together capture a diffuser and integral dispersing baffle that are further formed with an uptake lumen or channel terminating with a nozzle jet. The diffuser dispersing baffle is positioned relative to the jet nozzle to optimize atomization of any of a number of such substances so as to maximize disbursement of the substance. The reservoir base also incorporates a pressurized fluid-accelerating inlet tube terminated with a metering orifice that cooperates with the nozzle jet when the inlet tube is received within the diffuser uptake lumen or channel. When so received, the nozzle jet axially registers proximate and superior to the orifice to establish a vacuum space that is in fluid communication with a capillary interstice established between the walls of the exterior of the inlet tube and the confronting interior surface of the diffuser lumen or channel. When a pressurized fluid is communicated through the lumen, the orifice, and into the vacuum space towards the nozzle jet, a vacuum develops in the vacuum space that, in combination with the capillary action of the interstice, draws the fluid proximate to the orifice and disperses it into droplets that are then entrained into a fluid stream to be further atomized upon impact with the baffle and then dispensed.