Plegridy (peginterferon beta-1a) for multiple sclerosis

Last updated June 23, 2025, by Andrea Lobo, PhD
Fact-checked by Inês Martins, PhD

What is Plegridy for MS?

Plegridy (peginterferon beta-1a) is an approved injectable medication used to treat adults with relapsing forms of multiple sclerosis (MS), including clinically isolated syndrome (CIS), relapsing-remitting MS (RRMS), and active secondary progressive MS (SPMS).

Taken via intramuscular or subcutaneous injections — that is, directly into the muscle or under the skin — it is used to reduce the frequency of MS relapses, lower the number of lesions, and slow disability progression.

While the exact mechanism through which Plegridy works in MS is not fully understood, it works similarly to other interferon beta-1a medications, reducing excessive inflammatory responses to lessen nerve cell damage.

However, the interferon molecules in Plegridy are modified with a molecule called polyethylene glycol, which allows the therapy to maintain its biological effects for longer periods, allowing for less frequent dosing.

The therapy was developed and is marketed by Biogen.

Therapy Snapshot

Brand name:	Plegridy
Chemical name:	Peginterferon beta-1a
Usage:	Used to reduce disease activity and slow disability progression in relapsing forms of MS
Administration:	Subcutaneous or intramuscular injection

Who can take Plegridy?

Plegridy is approved in the U.S. for adults with CIS, RRMS, and active SPMS.

The therapy is contraindicated for people with a history of hypersensitivity reactions (harmful immune responses, including allergic reactions) to natural or lab-made interferon beta, peginterferon, or any other component of Plegridy.

The medication is approved in dozens of other countries worldwide, although indications may vary. In the European Union, for example, Plegridy is approved only for adults with RRMS.

How is Plegridy administered?

Plegridy is given every two weeks via intramuscular or subcutaneous injections, which can be self-administered by patients or caregivers after appropriate training.

The recommended dosage is 125 micrograms every 14 days, but to minimize potential flu-like symptoms, patients using Plegridy for the first time should start with a lower dose and gradually increase to the full dose over the course of one month.

A doctor may also recommend taking analgesics or anti-fever medications to prevent or ease flu-like symptoms.

For those receiving Plegridy via subcutaneous injections, the medication is available as prefilled syringes or pens and should be injected into the stomach region, thighs, or back of the upper arm. A titration kit, called a Plegridy starter pack, is available to help patients slowly increase their dose when beginning treatment.

For patients prescribed Plegridy for intramuscular injections, only pre-filled syringes are available, and injections should be given into the thigh muscle. A Plegridy titration kit is provided when starting treatment to help with accurate dosing during the titration period.

Regardless of the method of administration, injection sites should be rotated to avoid injection site reactions.

Plegridy in clinical trials

Plegridy’s approval in the U.S. was largely based on data from the Phase 3 ADVANCE trial (NCT00906399), which involved 1,512 adults with RRMS and randomly assigned them to receive Plegridy or a placebo for about one year. ADVANCE showed:

Plegridy given every other week significantly reduced relapse rates, by 35.6%, compared with a placebo, meeting the trial’s main goal.
It significantly reduced the proportion of patients experiencing 12-week sustained disability progression.
It outperformed a placebo at reducing the number and volume of new or enlarging lesions, as well as the number and volume of lesions with active inflammation or with irreversible nerve cell damage.

Results from ADVANCE’s second year, where placebo-treated patients switched over to Plegridy, and the long-term ATTAIN extension study (NCT00525343) showed sustained benefits for up to six years.

Plegridy side effects

The most common side effects of Plegridy, based on clinical trials of the subcutaneous formulation, include:

injection site reactions, such as redness, pain, and itching
flu-like symptoms
fever
headache
muscle pain
chills
generalized weakness or lack of energy
joint pain.

People taking Plegridy may experience some serious side effects, which may require more careful monitoring or treatment discontinuation, including:

liver injury, which may include hepatitis or, in rare cases, liver failure
depression and suicidal thoughts
serious allergic reactions, including anaphylaxis, angioedema (swelling), or hives
injection site reactions, which in rare cases may lead to tissue death at the injection site
heart problems, including congestive heart failure
low blood cell counts, which may increase the risk of infections, bleeding, or anemia
thrombotic microangiopathy, a rare condition involving blood clots in small vessels that can be life-threatening
pulmonary arterial hypertension, or high blood pressure in the lungs, which may require stopping treatment
new autoimmune disorders, such as autoimmune hepatitis or thyroid issues
seizures.

Multiple Sclerosis News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.

FAQs about Plegridy

When was Plegridy approved by the FDA?

Plegridy was first approved by the U.S. Food and Drug Administration in August 2014 as a subcutaneous injection to treat relapsing forms of multiple sclerosis (MS). It is indicated in the U.S. for clinically isolated syndrome, relapsing-remitting MS, and active secondary progressive MS. The intramuscular formulation was approved in 2021.

Can I take Plegridy while pregnant?

Data from several observation studies have not found an association between exposure to interferon beta medications before conception or in early pregnancy with a higher risk of fetal issues or major birth defects. Where clinically needed, Plegridy may be considered for use during pregnancy, but patients who plan to become pregnant should discuss this possibility with their healthcare providers.

Can I drink alcohol while taking Plegridy?

Interactions between Plegridy and alcohol have not been reported to date. However, alcohol may exacerbate some side effects of Plegridy, such as liver injury, so patients are advised to discuss with their healthcare team whether it is safe for them to drink alcohol.

How long should I wait to see the results of Plegridy?

In clinical trials, significant benefits from Plegridy were reported after one year of treatment, but results may have been evident for some patients in earlier assessments. It is difficult to predict when and how someone will respond to a medication, so patients should talk with their healthcare providers to better understand how Plegridy can help with their unique situation.

Does Plegridy cause hair loss or weight gain?

Hair loss (alopecia) was a common side effect experienced by patients on Plegridy in clinical trials. Although more rarely, weight gain also may occur as a result of kidney damage caused by the medication. Patients should inform their healthcare provider if any unexpected symptoms develop.