I am a doctor and my patients often ask me the following three questions:
1. Is tobacco in general, and smoking in particular, haram, Makrooh or permissible?
2. Can a patient use inhaler while fasting? Inhaler delivers the medicines to lungs in the form of very tiny particles. These pass through the throat into the lungs. So can it be used or not?
3. Nebulizers convert liquid medicines into mist which is delivered to lungs for treatment of asthma and similar conditions. Can it be used while fasting?
Smoking has not been regarded as haram in the shariah. The shariah does not touch upon such topics. In fact, it has left the prohibition of things which are injurious to health to the wise discretion of human beings. Countries can enact laws which prohibit smoking. The sphere in which Islam gives its directives is the moral sphere.
However, there are some people who erroneously derive the prohibition of smoking from a verse of the Qur'an. For details, please see: http://www.youtube.com/watch?v=IOQHWh2-ims
Use of the inhaler and nebulizer while fasting cannot be regarded as prohibited because nothing enters the stomach in the process.