Multiple life cycle analyses have consistently shown that the vast majority (90-98%) of the carbon footprint of a spray inhaler comes from the propellant gas in the canister. The carbon footprint of an inhaler, therefore, depends massively on the amount of propellant gas used (HFA134a or HFA227ea in current spray inhalers) and how powerful that gas is as a greenhouse gas.
In the 2021 IPCC assessment report 6, we saw updated values on how powerful these greenhouse gases are thought to be. The 100-year global warming potential (GWP) of HFA134a, which is used in most inhalers, increased from 1,300 times that of CO2 to 1,530 times. This means that, based on the most up-to-date figures, the carbon footprint of inhalers containing HFA134a is probably about 18% greater than we previously thought.
HFA227ea inhalers are less common (mainly Flutiform in the UK) but its carbon footprint has increased as well. The GWP of HFA227ea has increased from 3350 to 3600; an 8% increase.
Sorry for the depressing news, but a Ventolin evohaler actually has a carbon footprint of about 31.5kg CO2e per device, and Flutiform is about 39kg.
The good news is that newer propellants are being developed at pace, and initial results suggest they could work really well. HFA152a has a carbon footprint 164 times that of CO2, and plans are in place to make this available from 2025. Similiarly HFO1234ze shows a lot of potential and has a carbon footprint very similar to CO2. What we really need is a blue reliever inhaler with a small carbon footprint, as this is the most commonly used inhaler worldwide. GSK who make Ventolin evohaler have set themselves a target of net zero by 2030 so hopefully, within the decade we will have effective safe alternatives.