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There are two ways (from my thought) to perceive the "meaning" of extended release as it pertains to medication (or supplements, whatever) and I cannot logically decipher which would be the case. I get that these dissolve over a certain period of time and I'm completely indifferent as to the process; I want to know whether a 10 mg ER tab, for instance, releases the full 10 mg consistently throughout the stated time-period OR releases a much smaller amount OF that 10 mg throughout the day. (In the second instance, I imagine the amount released at any given moment would be the number of hours relatively divided by the 10 mg resulting in a far lesser amount existing in the system at any given time.)

As it is, the concept of "extended release" on its own without this added perspective is a bit ambiguous. (If it is relevant, I am asking more specifically about morphine ER.)

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10 mg is the entire quantity of drug present. It wouldn't really be possible to describe the rate at which the drug is released in just 1 number, and if so, it would have to be in units of "mass per time" rather than just "mass."

The time course of extended release depends on the formulation. Typically the release will be faster early on, however the result of extended release is to a) reduce the peak plasma concentration, b) increase the time to peak, and c) increase the length of time at effective doses.

For oral morphine, I quickly found the Collins et al 1998 paper, which might be a bit outdated, but it reviews many prior papers and compares peak plasma concentrations for various oral morphine formulations. In general, the total dose-corrected peak was ~50% for controlled vs immediate release, and the time of peak was around 3 hours rather than around 1.5 hours. There is a lot of variance between formulations, however, so these numbers may not apply to any particular formulation, just a general ballpark idea.


Collins, S., Faura, C., Moore, R. A., & McQuay, H. (1998). Peak plasma concentrations after oral morphine: a systematic review. Journal of pain and symptom management, 16(6), 388-402.

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