How can drugs such as Methadone have such a long half-life without giving you an overdose?

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How can drugs such as Methadone have such a long half-life without giving you an overdose?

In: Biology

Half life and overdose levels aren’t quite related. If you’re given a single, safe dose of the drug at a time (letting the drug completely clear from your body between doses), you’ll never overdose on it, no matter how long the half-life is.

Similarly, the half-life is irrelevant to how much of the drug is needed for an overdose, although a short half-life would also shorten the duration of the overdose.

A dose is related to how much of the drug is needed to achieve a certain concentration in your blood. Most medications need to achieve a certain concentration in order to be effective / do their job / kill all the bacteria / whatever.

The half-life is related to how fast your liver can decompose the medication or substance (alcohol for example). Your liver works 24/7 and decomposes nutrients and chemicals in your blood, and the kidneys sometimes participate in the decomposing, but primarily extract the by-products created by the liver, into your urine.

So basically, each dose is decomposed by the liver within a certain time, which is why you need to take another dose in order to maintain the “working concentration” for the medication to be effective over a period of days or weeks.

Anyway, long half-live means the liver doesn’t decompose it easily. The (normal) dose just goes around in your blood without being taken out by the liver and the kidneys.