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Psychiatric medication

Explains what psychiatric drugs are, what to know before taking them, and information on side effects and coming off medication.

What is a drug's half-life?

The half-life of a drug is the time it takes for the amount of a drug’s active substance in your body to reduce by half. This depends on how the body processes and gets rid of the drug. It can vary from a few hours to a few days, or sometimes weeks.

No matter what dosage of a drug you're on, or how long you've been taking it for, its half-life is always the same.

Why does my medication's half-life matter?

A drug's half-life matters because:

  • a short half-life usually means more withdrawal problems
  • a long half-life usually means fewer withdrawal problems.

If you are taking a drug with a short half-life and having problems with withdrawal, it might be possible for you to switch to a similar drug with a longer half-life. This longer half-life drug might be easier to come off.

The half-life can also be a guide for how long a drug will take to reach a stable level in your body when you first start taking it. Generally, it will take about five times the drug's half-life to build a stable level in your body. Once a drug's level is stable in your body, any early side effects you experience from the drug may start to decrease.

Where can I find the half-life of my medication?

You can compare the half-lives of different types of drug by looking at our comparison tables for:

The half-life given for any drug is not an exact figure. It can vary a lot between different people. These tables should only act as a guide.

This information was published in March 2021. We will revise it in 2024.

References and bibliography available on request.

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