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I have seen lot of people sleep or say that they are feeling sleepy after taking some medicines. Why? I mean, if a medicine acts on some cell of the body because that cell has got its receptors and other cells have receptor for another part of that molecule, then too why do a large range of medicine induce sleep?

This also points to a doubt that there are only one kind of receptors for sleep inducing medicines (the real ones not the ones which have sleep as side effect) or many? If many are there, then it can be possible that a large range of medicines induce sleep.

Is it due to induction of sleep gives relaxation and thus give time for action of other medicines? Or is it just a natural process? If latter, why only some?

I don't want metabolism, just a reason.

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  • $\begingroup$ Potentially too broad here - many medicines induce drowsiness/sleep but they may (and probably are, particularly comparing sleep medication and those that induce drowsiness as a side effect) by different mechanisms. I think you may need to narrow this down a little. $\endgroup$ – rg255 Jun 29 '15 at 15:59
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    $\begingroup$ I'm torn between flagging this as way too broad and thinking that it is a good opportunity to clear up basic misconceptions about drugs in an answer. In any case, I recently noticed that a standard book on pharmacology has three separate chapters entitled "how drugs act", this should give you a hint why the question is hard to answer in this state. Note that these were basic overview chapters, before delving into what specific classes of drugs do. $\endgroup$ – rumtscho Jun 29 '15 at 15:59
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    $\begingroup$ @InfiniteLight I don't see how reducing it to three-four mechanisms will help. "Why are there many medicines which are H1 receptor antagonists" is not a good question, there is no good reason why there are several of them. Also, I wouldn't say that some mechanisms are more "common" than others, common by what count? $\endgroup$ – rumtscho Jun 29 '15 at 16:14
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    $\begingroup$ @InfiniteLight - within the body naturally occurring compounds as well as medications (i.e. legal and prescription) target a variety of receptors (even if drug companies or other people say they specifically target one single receptor in the body). Almost ALL drugs we prescribe to patients have side effects that are off-target effects. Anti-histamines are probably the most common class that cause people to be sleepy. Even though those drugs "act" through one type of histamine receptor, another type of brain histamine receptor is also targeted unintentionally - causing sleepiness. $\endgroup$ – Vance L Albaugh Jul 3 '15 at 16:13
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    $\begingroup$ Voting to reopen this question. I disagree that it should have been closed for being too broad, because I think this question can be answered with a relatively concise answer that clears up the misconceptions present in the original question. $\endgroup$ – Bryan Krause Mar 1 '17 at 22:46