Comprehensive medication guide to Pegasys including estimated pricing, availability information, side effects, and how to find it in stock at your local pharmacy.
Estimated Insurance Pricing
$0–$150 specialty tier copay with prior authorization; Medicare Part D $2,000 annual out-of-pocket cap applies.
Estimated Cash Pricing
$1,095–$1,200 per vial or prefilled syringe; approximately $4,290–$4,800 per month at once-weekly dosing with no current generic or biosimilar available.
Medfinder Findability Score
25/100
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Pegasys is the brand name for Peginterferon Alfa-2a, a pegylated interferon used to treat chronic hepatitis B and chronic hepatitis C. It is FDA-approved for adults and children aged 5 and older with hepatitis C, and for adults and children aged 3 and older with hepatitis B.
Beyond its approved uses, Pegasys is widely prescribed off-label for myeloproliferative neoplasms (MPNs) including polycythemia vera (PV) and essential thrombocythemia (ET). It is administered as a once-weekly subcutaneous injection and requires refrigeration.
Pegasys carries a boxed warning about the risk of fatal or life-threatening neuropsychiatric, autoimmune, ischemic, and infectious disorders. Patients must be closely monitored with regular clinical and laboratory evaluations throughout treatment.
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Pegasys contains Peginterferon Alfa-2a, a pegylated form of recombinant interferon alfa-2a. The medication works by binding to interferon alfa receptors on cell surfaces, which activates intracellular JAK-STAT signaling pathways. This triggers antiviral, antiproliferative, and immunomodulatory effects throughout the body.
The polyethylene glycol (PEG) chain attached to the interferon molecule extends its half-life significantly. This is what allows Pegasys to be dosed once weekly rather than requiring multiple injections per week like older, non-pegylated interferons.
For hepatitis B and C, Pegasys helps the immune system fight the viral infection. For myeloproliferative neoplasms, it helps control the overproduction of blood cells by suppressing abnormal cell growth.
180 mcg/mL single-dose vial (1 mL)
180 mcg/0.5 mL prefilled syringe
135 mcg/0.5 mL prefilled syringe
180 mcg/0.5 mL autoinjector
135 mcg/0.5 mL autoinjector
Pegasys (Peginterferon Alfa-2a) has a findability score of 25 out of 100, making it one of the hardest medications to locate in the United States right now. There is an active FDA shortage affecting both the 180 mcg/mL vials and 180 mcg/0.5 mL prefilled syringes. The shortage began in 2024 after pharma& GmbH acquired the product from Roche, and increased global demand — particularly for off-label use in myeloproliferative neoplasms like polycythemia vera — has outpaced manufacturing capacity.
Supply is distributed through Summit SD and remains extremely limited. Manufacturing site expansions are underway in Europe, but the US supply restoration timeline remains uncertain heading into 2026. If you need Pegasys, Medfinder can help you locate pharmacies that currently have it in stock.
Pegasys is a specialty medication typically prescribed by the following types of doctors:
Because Pegasys requires close monitoring with regular blood work and clinical evaluations, it is not typically prescribed by primary care physicians. Patients usually receive their prescriptions through specialty pharmacies.
No, Pegasys is not a controlled substance. It does not have a DEA schedule classification and has no known potential for abuse or dependence. However, it is a specialty injectable biologic that requires a prescription, prior authorization from most insurance plans, and is typically dispensed through specialty pharmacies rather than retail pharmacies.
Serious side effects that require immediate medical attention include depression or suicidal thoughts, signs of infection, unusual bleeding or bruising, chest pain, vision changes, and signs of autoimmune disorders. Pegasys carries a boxed warning for neuropsychiatric, autoimmune, ischemic, and infectious complications.
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BESREMi (Ropeginterferon Alfa-2b)
FDA-approved for polycythemia vera and recommended by NCCN as a substitute during the Pegasys shortage. This is the closest alternative for MPN patients.
PegIntron (Peginterferon Alfa-2b)
another pegylated interferon historically used for hepatitis C, though largely replaced by direct-acting antivirals.
Harvoni (Ledipasvir/Sofosbuvir)
a direct-acting antiviral (DAA) for hepatitis C that has largely replaced interferon-based regimens.
Epclusa (Sofosbuvir/Velpatasvir)
a pan-genotypic DAA for hepatitis C.
Mavyret (Glecaprevir/Pibrentasvir)
another pan-genotypic DAA for hepatitis C with a shorter treatment course.
Hydroxyurea
used for polycythemia vera and essential thrombocythemia but works through a different mechanism.
Prefer Pegasys? We can find it.
Telbivudine
moderatecontraindicated; increased risk of peripheral neuropathy
Ribavirin
moderaterisk of hemolytic anemia; the combination is Category X in pregnancy
Didanosine
moderateincreased risk of hepatic failure, peripheral neuropathy, and pancreatitis; avoid combination
Azathioprine
moderateincreased risk of pancytopenia
Theophylline
moderatePegasys inhibits CYP1A2, increasing theophylline levels by approximately 25%
Methadone
moderateincreased methadone levels via CYP1A2 inhibition
NRTIs
moderateincreased hepatotoxicity risk in HIV/HCV coinfection
Myelosuppressive agents
moderateadditive bone marrow suppression
Pegasys remains a critical medication for patients with chronic hepatitis B, hepatitis C, and myeloproliferative neoplasms like polycythemia vera. Unfortunately, the ongoing shortage makes it extremely difficult to find — with a findability score of just 25 out of 100.
If your doctor has prescribed Pegasys and you're struggling to locate it, Medfinder can help you search pharmacies that currently have it in stock. You should also ask your doctor about BESREMi as a potential alternative for MPN indications, or direct-acting antivirals if you're being treated for hepatitis C.
For financial assistance, contact pharma& Patient Assistance at 855-443-7028 or check resources like NeedyMeds and RxAssist. With cash prices exceeding $1,000 per injection, it's worth exploring every option to reduce your out-of-pocket costs.
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Our medication guides are researched and written to help patients make informed decisions. All content is reviewed for accuracy and updated regularly. Learn more about our standards
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