Question: In order to see how the body interacts with drugs, do you make the radio-active equivalent of that drug in order to see how it is metabolised, turned into waste products etc?

Jack Heal answered on 20 Mar 2013:

Great question. It’s not always used, but it certainly can be done. The downsides are that you have to give the patient something radioactive, which is best avoided when possible.
You attach something tiny and radioactive to a drug to turn it into a radioactive drug. They are designed to emit a small amount of radiation over a very small distance (so as to affect as little of the body as possible!).
The radioactive drugs give off radiation which can be detected by a computer. And then you can detect when the drug is broken down, and where it goes in the body etc. If you make something like radioactive glucose then you can track the metabolic activity of different organs (basically, how much sugar they’re using – therefore how active they are). It’s most commonly used to look at tumours and to see if cancer is spreading in the body.