What medication takes the longest to get out of your system?

That's complicated. : Some drugs- used to treat osteoporosis, can take up to years- yet most drug half-lives are measured in hours to days. The other factors that influence a drugs half-life (how long they remain in our bodies, essentially) can be determined by other drugs, our metabolism, smoking, and the class of drug, such as pain or anxiety medications, etc.; it depend on what we're specifically talking about.