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Frequently Asked Questions

What do the acryonyms CD, CR, LA, SR, TR, XL and XR stand for?

Short Answer

CD - controlled delivery, CR - controlled release, LA - long acting, SR - sustained release, TR - timed release, XL - extended release, XR - extended release

Long Answer

These acronyms often appear in the names of tablets or capsules that are designed to deliver medication to the body over time as opposed to being immediately released when ingested. Two examples of these drug names are Detrol LA (Tolderodine LA) and Tiazac XL (Diltiazem XL). Extended-release medications are usually taken once or twice a day while the same drug in an immediate-release formulation may need to be taken three or four times a day.

There are various mechanisms used to enable the extended release of a drug into the body. In some cases the drug is encased in a coating that dissolves after a period of time to deliver the active ingredient. Different thicknesses of this coating enable the drug to be released in a staggered effect. In a diffusion system, the drug is released over time through a matrix of small openings in an outer membrane.

While the acronyms CD, CR, LA, etc., are often used interchangeably, patients should be aware that different extended-release versions of the same drug are not necessarily the same. As mentioned above, the mechanism used to disperse the drug can vary and this can affect how the drug acts on the body. Dosing instructions may differ; for example, Wellbutrin SR is taken twice a day while Wellbutrin XL is taken once a day. Also, some of these pills should not be crushed, chewed or divided while others can be safely divided but not crushed or chewed. When switching between different brands of the same drug, always check with your healthcare provider to find out if there are any differences you should be aware of.


Some medical conditions, such as hypertension and diabetes, can be controlled much more effectively with extended-release medication because a more consistent level of the drug is maintained in the bloodstream. In turn, this can reduce adverse reactions since the body isn't subjected to the sudden effect of medication hitting the bloodstream all at once. Because extended-release drugs are taken just once or twice a day, it's easier for patients to follow the dosing regimen and gain the most therapeutic benefit from the treatment.

Note: Delayed-release products do not fall into the same category as extended-release. Delayed-release are designed to release the drug into the body hours after the drug has been ingested. Between the time of ingestion and the time the drug is released, no absorption of the drug takes place.

Additional Information

A brief explanation of the various extended-release products and their acronyms.
Australian Prescriber
An in-depth article discussing oral extended-release products, their history, advantages and disadvantages, delivery mechanisms, and the types of drugs that lend themselves to this format.