Short Answer

If no visible (to the naked eye) droplets come out then it is fine and does not break your fast, such as a vicks vapoinhaler. An asthma inhaler emits a visible spray so it should normally break your fast, however, since the amount that reaches your stomach is so miniscule, it resembles the amount of water absorbed when rinsing your mouth with water, which does not break your fast.

What the Scholars Say

Contemporary scholars have disagreed whether an asthma inhaler will break your fast. One group says it will because it falls into the category of any visible substance being intentionally swallowed. The other group says it does not because it is intended to go to the respiratory system and not the stomach, so the tiny amount that reaches the stomach is unintentional and excused, just like when you rinse your mouth and some water unintentionally reaches your stomach.

My Opinion

I think both views are quite strong but slightly lean towards the opinion that it does not break the fast, even though the ingredients contain some elements that provide nourishment to the body, it is usually so miniscule that it is similar to the amount of water that is absorbed by your tongue or goes down your throat without you swallowing when you rinse your mouth for wudu.

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Shaykh Mustafa Umar