If you’ve taken an oral medication, like a tablet or capsule, you may have noticed different letters — like SR, ER, and CR — following the medication’s name. You may be wondering what they mean or if they change how the medication works. These letters signify a modified-release dosage form.

There are many different medication dosage forms and each has unique characteristics — as well as benefits and drawbacks — to suit your individual needs. The same goes for modified-release dosage forms, which change how the medication is released in your body.

In this article, we’ll review the different modified-release dosage forms and how they work in your body, as well as the best way to take them.

What are the different types of modified-release dosage forms, and how are they different?

The most common oral dosage form is an immediate-release (IR) medication. While there are some exceptions, an IR medication usually dissolves shortly after entering the body and works very quickly for a short amount of time. 

IR medications are absorbed and reach their peak level quickly. Medication levels will decline as your body removes it. This leads to varying medication levels in your body after taking a dose. For some medications, this could mean you need multiple doses in a single day to maintain a steady amount of medication in your body.

To make medications more convenient and better tolerated, many different dosage forms have been created to extend or delay their effects. These are known as modified-release dosage forms, and it’s important to know the difference between the most common ones — more on this below.

Extended release (ER)

An extended-release medication is usually labeled with “ER” or “XR” at the end of its name. Medications that have ER forms are designed to make them last longer in your body. This allows the medication to be taken less often compared to the IR version, so you may only take 1 to 2 doses a day instead of 3 to 4. 

Many different medications have ER forms, such as venlafaxine ER. This ER antidepressant is taken once daily, compared to venlafaxine IR, which is taken 2 to 3 times daily.

The term “extended release” is typically used as an umbrella term and can include medications that are both sustained- or controlled-release since they both allow for fewer daily doses.

Sustained release (SR)

Sustained-release medications are usually labeled with “SR” at the end of their name. These medications prolong the medication’s release from a tablet or capsule so that you’ll get the medication’s benefits over a longer period of time. This means that you may need to take fewer doses throughout the day.

One example of this is Calan SR (verapamil ER), which is dosed once daily, whereas the immediate-release form is dosed 3 times daily.

However, even though the medication is released over a longer period of time, it doesn’t mean the medication levels remain constant while it’s in your body. SR forms control the medication’s release, but not the amount in your body at a given time.

Controlled release (CR)

A controlled-release medication is usually labeled with “CR” at the end of its name. CR medications release the active ingredient(s) at a specific rate to keep constant medication levels in your body for a specific time period. This allows for more precise control of medication levels after taking it and fewer doses needed throughout the day. 

Unlike SR forms, CR medications can precisely control the amount of medication in your body at a given time, not just its release. 

The sleeping aid Ambien CR (zolpidem ER) is a good example of a CR medication. Ambien IR can wear off towards the end of the night, which might prevent some people from getting a proper night’s sleep. Ambien CR, on the other hand, releases the medication at a controlled rate to promote better sleep throughout the whole night.

Delayed release (DR)

Delayed-release (DR) medications are medications that are designed to release the active ingredient(s) later after taking it, which can help control where it’s released in the body (e.g., small intestines). This is usually done to prevent the medication from being broken down too early or lessen potential side effects.

Some DR medications cause the active ingredient(s) to be released in the large intestine (the colon) in order to reach the area being treated. For example, sulfasalazine DR is a medication used to treat ulcerative colitis — an autoimmune condition that causes inflammation in the colon.

Enteric-coated (EC or “safety-coated”) medications are also considered to be a DR dosage form. They have a special film coating that stops them from being broken down in the stomach. This prevents the medication from being released until it reaches the small intestine, which may help lessen certain side effects, like an upset stomach. 

Aspirin is a common medication that is available as an EC form.

Why is it important to understand the difference?

It’s important to understand how a medication is released after taking it so you can predict how your body will react. For example, an IR medication usually works more quickly than a modified-release medication. Additionally, its effects may wear off faster because the medication is released all at once instead of over a longer period of time.

Modified-release medication forms may take longer to start working. This is because they are typically absorbed more slowly, or they don’t start breaking down until they reach a certain area in your body. And some modified-release medication forms (like ER, SR, and CR) provide longer-lasting effects.

What are some disadvantages of modified-release dosage forms?

Modified-release dosage forms can be very useful in saving you time and allowing for fewer daily medication doses, but they also have some disadvantages. 

Modified-release dosage forms — particularly ER medications — can be much larger than IR forms. This can make them harder to swallow for some people. They also tend to be more expensive than their IR counterparts.

And in the event of a medication overdose, modified-release dosage forms may take more time to get out of your system because they’re designed to be in the body longer. 

Finally, since most modified-release dosage forms can’t be altered (e.g., cut, split, etc.), it may be difficult to adjust your dose if a specific strength isn’t available. 

Does pill-splitting, crushing, or chewing affect how the medication is released?

Most modified-release dosage forms shouldn’t be crushed, split, or chewed. When you cut a modified-release medication, the active ingredient may be released much quicker and at a higher concentration than intended, which can be dangerous. In other words, you’ll receive a dose that’s normally released over a longer timeframe all at once.

Also, the medication might not be able to reach the proper location in your body if the tablet or capsule is crushed, split, or chewed. This means you may not get the proper effects of the medication. 

However, some extended-release capsules, such as Adderall XR, may be opened up and mixed into applesauce for people that have problems swallowing the capsule. Always check with your healthcare provider or pharmacist before altering any of your medications

The bottom line

There are many different modified-release dosage forms available to help make taking medication more convenient. They are used for various reasons, such as taking fewer doses in a day, avoiding certain side effects, or better targeting the area being treated. 

While they make it more convenient to take, they are usually more expensive and can be more dangerous if not taken correctly. Talk to your healthcare provider to see if switching to a modified-release dosage form is right for you.