Many oral medications are available in several formulations that affect how the medication is released into your bloodstream. If your medication is followed by letters such as ER, XR, SR, CR, or DR, it means you’re taking a modified-release formulation. With these formulations, a medication’s effects are either extended over a longer period of time or delayed. They are often prescribed to decrease side effects or reduce the number of pills you have to take.

It’s important to understand how your body absorbs a medication. Read on to learn the key differences between the available medication formulations.

Immediate-release medications

The standard dosage form of most oral medications is immediate-release. If your medication is not followed by one of the letter combinations above, it typically means that you’re taking an immediate-release formulation.

These medications are both fast-acting and short-lasting. Your body absorbs an immediate-release medication quickly after it enters your bloodstream, with the medication effects peaking within a small window of time. This can lead to greater side effects in some cases.

Your body’s levels of an immediate-release medication decline as it leaves your bloodstream. As a result, many immediate-release medications require you to take multiple doses each day so that you maintain a consistent amount of it.

Extended-release medications (ER or XR)

An extended-release medication — typically indicated on the prescription label with an “ER” or “XR” after the medication’s name — prolongs a medication’s effects and its levels in your body. With many medications, this reduces the number of daily doses.

Examples of extended-release medications include:

• Alprazolam XR (Xanax®)

• Estradiol ER transdermal patch (Alora®, Climara®, Dotti®, Lyllana®, Menostar®, Minivelle®, Vivelle-Dot®)

• Metformin ER (Fortamet ER® , Glucophage XR®, Glumetza®)

• Metoprolol succinate (Toprol XL®)

• Tramadol ER (ConZip®, Ultram ER®)

There are two subtypes of extended-release medications: sustained-release and controlled-release. Since SR and CR formulations fall under the category of extended-release medications, they may be designated by an “ER” or “XR” after their name.

Sustained-release medications (SR)

A sustained-release formulation extends a medication’s release into your body, prolonging its effects over a longer period of time. They are typically prescribed to decrease the doses required on any given day.

While an SR medication’s release is gradual, it does not mean there will be a consistent amount of the medication in your body over time.

Controlled-release medications (CR)

A controlled-release medication is designed to keep a consistent amount of a medication in your body over a specific window of time. These medications differ from SR medications in that they precisely control medication levels in addition to decreasing daily doses.

Delayed-release medications (DR)

A delayed-release medication — typically designated by a “DR” after its name — releases a medication’s active ingredient more slowly. This controls where a medication is released in the body, often to minimize side effects. For example, if a medication is released in the small intestine, after it has already passed through the stomach, you are less likely to experience certain side effects such as nausea.

Examples of delayed-release medications include:

• Doxycycline hyclate DR (Doryx®, Doryx MPC®)

• Fluoxetine DR (Prozac®)

• Omeprazole DR (Prilosec®)

• Mesalamine DR (Asacol HD®, Delzicol®, Lialda®)

• Risedronate DR (Atelvia®)

Important considerations of modified-release medications

If you have concerns about medication side effects or dosing, you may want to ask your doctor if an extended-release formulation would be a good fit for your needs. Keep in mind that this may affect a medication’s cost and the size of the medication tablet or capsule. Additionally, many modified-release medications cannot be crushed or split, as this would potentially alter where and when the medication is released in your body, and, consequently, its effects.

The pharmacy care you deserve

Our expert pharmacists can answer any questions you have about medication side effects or release right in the Alto app. We also offer fast and reliable delivery and medication management tools like reminders and auto refills to make it as simple as possible to stay on track with your treatment.

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This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or another qualified health provider with any questions you may have regarding a medical condition.