I sometimes get asked by patients "how long do steroids stay in your system?" The answer to how long any drug effects your body is what's known as a drug's "half life." In very simple terms, the half life of a drug is the time it takes for half of the drug to be eliminated from your body. Not surprisingly, drugs with longer half lives stay in your system longer. Drugs with a shorter half life stay in your system for a shorter period of time and may need to be dosed multiple times per day.
While half life is mostly related to the properties of the drug, there are sometimes individual differences between patients that may make one drug work on you for a longer or shorter period of time compared to the average patient. For example, the half life of rescue inhalers like albuterol is in the 5 to 7 minute range while the half life of advair is 5 to 7 hours. A number of different things can affect the half life of a drug including age, gender, liver disease, kidney disease, and hydration.
Greenblatt DJ. Elimination half-life of drugs: value and limitations. Annu Rev Med. 1985;36:421-7.