Slow Release Drugs vs Sustained Release Vs Extended Release – The meaning

The Difference between sustained release and extended release tablets

When you see SR, CR, or XL on drugs or drug labels, what does it mean?

SR- Actually Sustained Release but many also refer to these drugs as slow release
CR- Controlled Release
XL- Extended release

They are ways in which drugs are formulated to control the ways the drug is released, absorbed, and metabolized in the system over time. This is to ensure minimal side effects, longer duration of action, and effectiveness.

More Details:

Long release drugs-

Confused yet?

XR. CR. SR ???

That medication might be considered an Extended Release (XR), but what does that mean?

Extended-release drugs fall into two categories.

Sustained-release (SR) or controlled-release (CR) .

Let’s get our heads around these jargon terms.

SR maintains drug release over a sustained period but not at a constant rate.

So a drug might last longer because it breaks down slowly in the gut, where it’s ability to be absorbed and therefore bioavailable is slowed. The amount released in the first hour is greater than the amount released in the following hour.

Eg. Frank takes RedPillicillin SR 1000mg twice per day 8am and 8pm.

In the first hour 300mg is released,
The next hour 200mg
Hour 3 – 150mg
Hour 4 – 100mg
5th hour – 75mg
6th hour – 50mg
7th hr – 40mg
8th hr – 30mg
9th hr – 25mg
10th hr- 15mg
11th hr – 10mg
12thhr – 5mg

At which time the next dose is due.

Controlled release (CR) drugs sustain their release but do so at a constant and predictable rate

Eg. Mona is prescribed Blackpillicilin CR 1000mg BD.

In the first hour and every hour there after, only 80-85mg is released till it’s all absorbed in around 12 hours. This allows a constant quantity of drug to enter Mona’s system offering g her a predictable and consistent dose over the full 12 hours.

Slow Release drugs
Slow release drugs.

Breaking XR tablets or capsules. All extended release medicines come with an enteric coating so breaking the tablet or crushing it to mush it in some thickened fluid may not be appropriate or safe. As a blanket rule, they should not be crushed.

Rarely, some CR or SR drugs are manufactured in micro-enteric coating beads, they are usually capsules that have what looks like 100s &1000s inside. While these sprinkle filled capsules can be opened, care must be taken not to crush the microbeads.


SR stands for sustained release, which means the medication is released slowly and over a longer period of time. CR stands for release, which also means the medication is released slowly, but at a more consistent rate.

A common example of an SR drug is olfen SR 100mg

XL stands for extended release, which means the medication is released slowly and over an even longer period of time than SR or CR.

A common example of extended release drug is depo provera and even implanon contraceptives. Depo provera is released slowly over a period of 3 months while implanon is released slowly over a period of 3 to 4 years.

Slow release drugs are tablets that are released slowly over an extended period.


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