Why Are Some Medications Taken Once A Day?

What Exactly is a Half-Life?

Dr. Chittaranjan Andrade, a psychopharmacologist writing in the Journal of Clinical Psychiatry (a United States peer-reviewed medical journal) explains that in order to maintain uniform blood levels and reduce the adverse effect risk, drugs with short half-lives need to be dosed more frequently, whereas drugs that have a long half-life stay longer in the body and so have a longer duration of action. Such drugs can conveniently be dosed once a day or even less frequently.

How It Works

Here's a simple example: Half life = reduction by half: If you take 100 milligrams of a drug with a 1-hour half-life, only 50 milligrams remain after 1 hour. Further decline: After a second hour, 25 milligrams remain, and after a third hour, 12.5 milligrams remain. Complete clearance: Four to five half-lives is when a drug is mostly eliminated from the blood. It is not when every drug stops working. Some drugs have effects that outlast their blood levels (aspirin's antiplatelet effect, proton-pump inhibitors, many drugs with active metabolites). The half-life of a drug can vary from person to person. Half-life measures elimination, which includes both metabolism and excretion. It can be influenced by several different factors, including your age, kidney function, and liver function. [1] (https://www.goodrx.com/drugs/medication-basics/drug-half-life), [2] (https://www.drugs.com/article/drug-half-life.html)

Why It Matters

Your medication's half life is very important and directly affects the dosing schedule that your doctor assigns: It tells doctors how often you need to take the medication to keep the right amount in your system. If you don't take it often enough you run the risk of not getting the full benefit of the medication, and if you take it too often you run the risk of overmedication and side effects. As always follow your doctor's instructions and do not alter the dosing schedule without their approval.