You CAN take an inhaler on a plane.
More Info: The Transportation Security Administration (TSA) has created guidelines for carrying inhalers onto a plane. Inhalers that weigh less than 3 ounces need to be placed in a clear plastic sealable quart-sized bag, and can be mixed in with other toiletries. If the inhaler is larger than 3 ounces, it should not be in a plastic bag. It must be declared to a TSA Officer verbally, in writing, or by the person's companion. It is recommended, but not required, that the label on the prescription match the passenger's boarding pass, and that any supporting documentation, such as a letter from a doctor, be carried. All items will go through X-ray; however, if you are concerned about the effect of X-rays on your medication, you can request that a TSA Officer manually inspect your item.
Could the Inhaler Explode Under Pressure?
There has been some discussion as to whether or not an inhaler will explode due to the pressure changes inside an aircraft. Both the cabin and the luggage hold are pressurized, so there is no risk of an inhaler exploding.
Countries Outside the US
These guidelines apply to flights in the United States. If you are flying outside of the US, check with the airline you will be flying with to determine whether an inhaler will be allowed. Also, check the requirements for the country you will be flying to, as they may have regulations regarding the types of medication that can be brought into the country.