All medications possess an active life, or total time during which they perform their curative activities within the body.
A drug’s half-life is the time in which it takes for the three metabolic processes to impact a given drug to the extent that one half (50%) of said drug is no longer present within the body’s system. Again, since drugs have varying chemical structures this time frame will also vary. Sometimes there are stark similarities within classes of drugs, e.g. oral steroids typically possess what we consider to be short half-lives of often between 4-16 hours. However, this is merely a generalization over most of the class, as some other types of orals fall outside these parameters for different reasons.
This half-life is reduces the drug content by 50% every time it is experienced, i.e. after the first half-life you’re at 50%, the second takes you to 25% or half of the remaining fifty, the third 12.5%, and so on until the last half-life known as the terminal one occurs…generally accepted as the 8th (below .05%). Although metabolites still exist, thereby making detection possible, the drug’s actions or active life has effectively ceased. However, as long as you continue taking a drug prior to the realization of the terminal half-life, you reinitiate its property actions thereby resetting the half-life quotient to a full 100%. Also of importance here is the fact that the more medication you take the greater the concentration in your blood becomes, until you achieve full blood serum saturation. Some people believe achieving full saturation somehow alters the half-life principle, but it doesn’t. Saturation has to do with optimizing the effects you receive from a medication over time, but it still succumbs to the principle of half-life because even though you can have more of drug in your system (amount-wise), you can never exceed the maximum of 100%. Consequently, whenever you reach the hundred percent mark be it the first drug administration or after taking it for several weeks, months or years once the first half-life expires the drug amount is necessarily reduced to 50%.