 Welcome to nursing school. Explain in this video on medication half-life. This is a very important topic to understand when it comes to the pharmacodynamics and pharmacokinetics of the medications. So a half-life that's also abbreviated as T one-half means how long or the amount of time that it takes for half of a medication to be eliminated from the body. So for example, diazepam has a very long half-life of 48 hours. That means half of the diazepam is going to be eliminated after 24 hours which is half of the 48 hours. If we look at it on this graph here, it might be a little bit easier to understand. So here we have the medication concentration and down here we have the half-life T one-half. So at point zero, right when we give the medication, the concentration is at its highest at 100%. But then because we know the half-life is 48 hours, so after one half-life 50% of the medication is going to be eliminated. After two half-lives 25% of the medication are going to be eliminated. After three half-lives that'll be half of the 12 of the 25 which is 12.5 and then after four half of that will be 6.25. And sometimes it can be a little bit confusing as to how does it go down. But it's really always only half of the medication gets eliminated but the time frame stays the same. So the half of the 48 hours is 24 we said. So one half-life is 24 hours, two half-lives is just 24 hours added to that. So 48, three half-lives would be an additional 24 which is 72 hours and then four half-lives in this case would be 96 hours. And typically after four to five half-lives the medication has no effect on the body because the concentration is just so small. However it may still be detectable on a blood test. So this is important especially in addiction medicine for example or when we run a drug test on patients because the patient might not be exhibiting any signs or symptoms of whatever medication or illegal substance that they took but it may still be detectable in the body and that is because of the drugs half-life. So also this principle is very important when it comes to the steady state of a medication which I'll explain in a different video. So please head on over to that video to check out the details there. Thanks for watching.