A 120mg pill of Sudafed (Pseudoephedrine hydrochloride), for example, lasts for 12 hours. You are not supposed to take another Sudafed pill before the 12 hours are up.

How exact is this 12-hour limit? Do i have to wait at least exactly 43200 seconds between pills? How much leeway is there? Could i take the second pill a few minutes (5? 10? 30?) before the time is up?

Note that Sudafed is used as an example here. The same should apply to any other drug with a time limit.

  • 2
    Are you asking specifically about Sudafed, or in general (as title suggests) and Sudafed is just example?
    – kenorb
    Apr 2, 2015 at 23:21
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    @kenorb My last sentence clearly states that it Sudafed is an example.
    – Scimonster
    Apr 3, 2015 at 3:06
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    The question is very broad, especially considering the last line "Should apply to any drug with a time limit". Does not take into consideration any other medications or health issues of the person, or that some people metabolize medications faster or slower than others.
    – JohnP
    Apr 17, 2015 at 21:00
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    I'm voting to close this question as off-topic because in case of doubt, only a doctor or a pharmacist can valuably answer
    – Shlublu
    Apr 17, 2015 at 22:36
  • If this were edited to one specific medication, maybe we could keep it, but I'm voting to close for now because the limit depends on so many things. First there's the metabolic rate as John mentioned, then there's the amount per time that doctor's tell you to take using an estimation of your metabolic rate, and then there's the possibility that skipping one may require you to take more during your next intake OR it could be that you must keep taking the same amount to avoid an overdose, and so on.
    – Dave Liu
    Apr 17, 2015 at 22:39

1 Answer 1


Good question though a broad one!

Well, it all depends on the 'pill' or 'medicine' you are on. Different medicines have different half-lives. And 'half-life' is the factor that mostly decides the 'dosage/timings'.

But, if you go by general guidelines, all doctors agree upon one thing:

Take a missed pill the moment you remember it. But then, if it is almost the time for the next dose, skip it. That said, don't ever take two pills together (compensating the missed dose).

The best practice is ask your healthcare provider about it. They can precisely tell you what should you do (though most of them would advise what I wrote).

  • 1
    I clicked on this question to give an answer almost identical to yours, although I would recommend that you move more information from the third party link into your answer ( in particular include some information about therapeutically effective concentration ) Apr 4, 2015 at 15:17
  • This has the makings of a good answer, but here on Health, we strongly encourage using references. They are the only way in which we can tell if information is reliable or not. If you are struggling to find good sources, check out, What are reliable sources? If you want to learn more about our site's stance on answers without references, check out, Should answers without references be immediately deleted?
    – Dave Liu
    Feb 13, 2016 at 3:16

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