It's such a tiny puff of air that sprays out of an inhaler to ease your breathing. But each dose contains some of the most potent greenhouse gases known, and they add up. By the time some inhalers are used up, they have emitted as much greenhouse gas as the average gas-powered car after being driven 60 miles.
In total, more than 70 million inhalers are prescribed in the United States each year and, together, they contribute more pollution to the atmosphere than the yearly electricity use of 200,000 American homes.
Those comparative data points highlight a new study, published in JAMA, by researchers at Stanford Medicine, University of Michigan and the National Health Service of England. The team used data from the U.S. Centers for Medicare & Medicaid Services to determine how many prescriptions of different types of inhalers were prescribed to Medicare and Medicaid beneficiaries in 2022 and calculate the total greenhouse gas emissions of each.
"There was a really wide range of emissions between different inhaler types, and it turns out that in the U.S. we're still mostly prescribing the inhalers that are the worst when it comes to emissions," said Jyothi Tirumalasetty, MD, a clinical assistant professor of pulmonary, allergy and critical care medicine and first author of the paper. "But there are some easy replacements for those inhalers, and we hope that patients and providers consider emissions when they choose an inhaler."
A tool for lung health
Inhalers may contain one or more medications to aid in breathing. Inhalers that contain bronchodilators, for example, deliver medication to a person's airways and lungs to relax the surrounding muscles, allowing air move in and out of the lungs more easily. Inhalers are commonly prescribed to people with asthma or chronic obstructive pulmonary disease to prevent or treat shortness of breath.
Today, there are three main types of inhalers: metered-dose inhalers, which use a propellant gas to push medication powerfully into the lungs; dry-powder inhalers that contain doses of medicine in particle form that must be breathed deeply in; or soft-mist inhalers that turn liquid medication into a mist.
In studies carried out in Europe, researchers showed that metered-dose inhalers emit high levels of hydrofluorocarbon propellants, which are thousands of times better at trapping heat in the atmosphere than carbon dioxide and are a key player in accelerating global warming. In part because of that data, the National Health Service of England -- as well as policymakers in countries including Sweden and Canada -- have encouraged clinicians to switch to dry-powder and soft-mist inhalers.
"We wanted to address this issue in the United States but realized we had no U.S. data for our inhaler use and emissions," Tirumalasetty said. "We had data from inhalers only in other countries, so we set out to change that."
Quantifying greenhouse gases
Tirumalasetty and her colleagues used safety data provided by the manufacturers of 37 major inhalers used in the U.S. to calculate the gases contained in each inhaler. Then, they used data from CMS -- covering more than a third of all prescriptions filled in the U.S. -- to determine which inhalers were being prescribed most often, as well as the costs for each inhaler.
The emissions of individual inhalers were close to one for dry-powder and soft-mist inhalers, and ranged from 9 to 48 kg of CO2 equivalent emissions for metered-dose inhalers. That puts some inhalers on par with the carbon footprint of a pound of beef. Some of those emissions came from each puff of the inhaler, while the rest were from propellant gases that remained in an inhaler after all the medication had been dispensed.
"When you throw a used inhaler in the trash, there are hydrofluorocarbons left in it that slowly leak into the atmosphere," Tirumalasetty explained.
When you throw a used inhaler in the trash, there are hydrofluorocarbons left in it that slowly leak into the atmosphere.
Jyothi Tirumalasetty
Of nearly 70 million CMS inhaler claims in 2022, metered-dose inhalers accounted for 70% of the claims and 98% of the total emissions attributed to inhalers. However, dry-powder and soft-mist inhalers were disproportionately expensive (some dry powder exceeding $1,000), and total costs can average nearly double that of metered-dose inhalers, despite representing fewer claims.
"This means that cost is potentially a barrier to the transition from metered-dose inhaler," Tirumalasetty said. "However, we're finding that those costs don't necessarily translate to out-of-pocket costs for patients. Someone may not be paying more for one inhaler over another."
Balancing the variables
Tirumalasetty and her collaborators hope that the new numbers inspire patients, providers and policymakers to think twice about which inhalers they use or recommend. But they also point out that metered-dose inhalers are not disappearing anytime soon, and prescription decisions must be made on an individual basis.
"We don't want to put patients in a place where they can't afford their inhalers or where they're using an inhaler that doesn't work as well to control their condition," Tirumalasetty said
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She admits that even at Stanford Medicine, any changes to inhaler prescription recommendations are still a work in progress; she has not yet changed her own prescribing behavior after seeing the new emissions data because of concerns about out-of-pocket patient costs. Her team, however, is working with Stanford Health Care to determine which costs are passed on to their patients and how this might shape patient preferences about inhalers.
"Ultimately, we'd like to have a nice, simple handout that tells patients, for each inhaler, what the cost is and what the emissions are, so they can decide," she said.
Funding for the research was provided by the National Center for Advancing Translational Sciences and the U.S. Department of Veterans Affairs HSR Investigator-Initiated Research program.