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Some questions about half life


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If the half life of a drug is 40 hours, does this mean that if you take another drug there is a danger of interaction? Also, will you still feel the effects of the drug if half of it has cleared your system? I am confused about this.

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The answers to your questions are "yes" and "yes".

 

The half-life is the time it takes for half of the drug to leave your system. A drug is usually not considered cleared of your system until 3-5 half-lives have passed.

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Thanks! I tried talking to the pharmacist, but they were not very helpful and referred me to my doctor.  I won't be seeing him until Friday and I just wanted some idea of what to expect.  I don't plan to take any more of my current med and wanted to go back on the other one while waiting to see the doc.

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Thanks! I tried talking to the pharmacist, but they were not very helpful and referred me to my doctor.  I won't be seeing him until Friday and I just wanted some idea of what to expect.  I don't plan to take any more of my current med and wanted to go back on the other one while waiting to see the doc.

 

All that being said, don't mess with your medications without speaking with a doctor ;)  You can get really sick.

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Half life doesn't always correspond to duration of action. For example Valium has a very long half life (days) but if you are taking it on a schedule you'll generally be prescribed 2-4 doses per day.

Thanks for clarifying that.   Its puzzled me why it didn't affect me for a longer period of time.   Is the half life in the case of Valium just how long its detectable?

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Half life doesn't always correspond to duration of action. For example Valium has a very long half life (days) but if you are taking it on a schedule you'll generally be prescribed 2-4 doses per day.

Thanks for clarifying that. Its puzzled me why it didn't affect me for a longer period of time. Is the half life in the case of Valium just how long its detectable? Half life is the time it takes for the level of the drug to fall to half of what you originally took.

I'm not sure why the effect of the drug wears off much quicker than that.

The reverse is sometimes true as well. Some drugs have a duration of action longer than the half life. Seroquel XR and Cymbalta are some examples of that. They are once a day drugs but the half lives are quite a bit shorter than 24 hours.

The way it all works is pretty complex. I don't understand it too well.

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