How to Know If Your Asthma Inhaler Is Empty

HFA-based metered-dose inhalers (MDIs) contain a propellant to deliver the medication that will continue to spray even after the medication has run out. Therefore, when the medication is gone from the inhaler, it is possible to continue to inhale only propellant and no medicine. This can be dangerous, especially in the case of rescue inhalers that are used to treat asthma symptoms in an emergency.

Anxious boy using an inhaler outdoors
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If your inhaler has a dose counter, this eliminates all the guesswork and uncertainty about how much medicine is left in an inhaler. For example, Ventolin HFA, Advair HFA, and Flovent HFA have dose counters,

Some asthma inhalers do not have a dose counter on the inhaler. And if you are taking an HFA-based metered-dose inhaler (MDI) without a dose counter, knowing when the inhaler is empty or close to being empty can be a challenge.

Calculating When You Don't Have a Dose Counter

Some inhalers that contain steroids are prescribed to be taken on a schedule to prevent asthma symptoms from occurring: For this reason, they often are called "controller" inhalers. Since they typically are used a predetermined number of times per day (or week), it's possible to determine when the inhaler is empty in three simple steps:

  1. Note the number of inhalations contained in your asthma inhaler when it is new from the pharmacy. This number should be clearly printed on the box or you can ask your pharmacist. For most steroid inhalers, this number is 120.
  2. Consider the number of puffs you are prescribed to take every day from your inhaler.
  3. Divide the number of inhalations in the device by the number of puffs you take each day. This will tell you how many days the medication will be available.

For example, if your inhaler contains 120 inhalations and your healthcare provider has prescribed two puffs twice a day, that's a total of four puffs per day. One hundred twenty divided by four equals 30; therefore, your inhaler will last 30 days.

When you obtain their new inhaler, it helps to write the “empty date” on the inhaler with a Sharpie marker. For example, if a new inhaler is started on October 1, then write October 31 on the inhaler. This will remind you to get a new inhaler on October 31, even if the old inhaler continues to spray propellant.

This system doesn’t apply to albuterol (rescue) inhalers, since most people don’t use this medication on any regular basis. Instead, These medications are used when an asthma attack is occurring. If your albuterol seems to be less-than-half-full when they shake it, it could be time to get a new one.

A Word From Verywell

For some people with mild to moderate persistent asthma, the math may be a bit more complicated. According to updated recommendations about asthma treatment from the National Institutes of Health (NIH) issued in December 2020, individuals in this group may not need to use an inhaler every day to control their asthma. If this applies to you, talk to your healthcare provider about how to calculate how long your inhaler will last.

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Sander N, Fusco-Walkert SJ, Harder JM, Chipps BE. Dose counting and the use of pressurized metered-dose inhalers: running on empty. Ann Allergy Asthma Immunol. 2006 Jul;97(1):34-8. doi: 10.1016/s1081-1206(10)61366-x

  2. Cloutier MM, Baptist AP, Blake KV, et al. 2020 focused updates to the asthma management guidelines: A report from the national asthma education and prevention program coordinating committee expert panel working group. Journal of Allergy and Clinical Immunology. 2020;146(6):1217-1270. doi:10.1016/j.jaci.2020.10.003

By Daniel More, MD
Daniel More, MD, is a board-certified allergist and clinical immunologist. He is an assistant clinical professor at the University of California, San Francisco School of Medicine and currently practices at Central Coast Allergy and Asthma in Salinas, California.