What Is Pegasys? Uses, Dosage, and What You Need to Know in 2026

Pegasys is a specialty injectable medication prescribed for serious conditions including chronic hepatitis B, chronic hepatitis C, and — off-label — blood disorders like polycythemia vera. If your doctor has prescribed Pegasys or you want to understand what it does before starting treatment, this guide covers everything you need to know.

What Is Pegasys?

peginterferon alfa-2a, a type of medication called a pegylated interferon. It is a modified form of interferon alfa-2a — a protein that your body naturally produces in response to viral infections. The "pegylated" part refers to a chemical modification (attachment of a polyethylene glycol chain) that slows the drug's breakdown in the body, allowing it to work longer with a once-weekly injection.

Pegasys was first approved by the FDA in 2002 and is on the World Health Organization's List of Essential Medicines. It is manufactured by zr pharma& GmbH (which acquired it from Roche in 2021) and is available as a subcutaneous (under the skin) injection.

What Is Pegasys Used For?

Pegasys has two FDA-approved indications:

• Chronic Hepatitis C (CHC): In adults and children 5 and older with compensated liver disease. Used alone or (more commonly) in combination with ribavirin or other antiviral medications. Cure rates (SVR) with Pegasys-based therapy range from 24% to 92% depending on the genotype and patient factors.
• Chronic Hepatitis B (CHB): In adults and children 3 and older with compensated liver disease and evidence of viral replication and liver inflammation (both HBeAg-positive and HBeAg-negative). Pegasys is one of few hepatitis B treatments that offers a finite treatment course with the potential for HBsAg seroconversion.

Pegasys is also used off-label for:

• Polycythemia vera (PV): NCCN guidelines recommend Pegasys for PV, particularly for younger patients or where hydroxyurea is contraindicated
• Essential thrombocythemia (ET) and primary myelofibrosis (MF): Also recommended by NCCN for select patients
• Certain T-cell lymphomas: Including mycosis fungoides

Pegasys Dosage and How It Is Given

Pegasys is given as a subcutaneous injection — a shot under the skin into the thigh or abdomen — once a week. The standard adult dose is:

• Standard dose: 180 mcg once weekly
• Reduced dose (severe renal impairment): 135 mcg once weekly (CrCl <30 mL/min)

Treatment duration varies by condition:

• Hepatitis C genotype 1: typically 48 weeks (combination therapy)
• Hepatitis C genotype 2 or 3: typically 24 weeks
• Hepatitis B: typically 48 weeks
• MPNs (off-label): typically long-term, dose-escalated based on response

Available Formulations

Pegasys is available in three forms:

• Single-use vials: 180 mcg/mL — requires drawing up a dose with a syringe
• Prefilled syringes: 180 mcg/0.5 mL — preloaded and ready to use
• Pegasys ProClick Autoinjector: 180 mcg or 135 mcg/0.5 mL — pen-style autoinjector for easy self-injection

How to Store and Handle Pegasys

Pegasys must be refrigerated at 36°F to 46°F (2°C to 8°C). Do not freeze it or shake it. It can be left out of the refrigerator for up to 24 hours but must not be used after that point. Keep it in its original packaging to protect it from light. All vials and syringes are single-use only — discard any unused portion.

Is Pegasys a Controlled Substance?

No. Pegasys (peginterferon alfa-2a) is not a controlled substance. It has no DEA schedule and no known potential for abuse or dependence. However, it is a specialty biologic that requires a prescription, prior authorization from most insurance plans, and is dispensed through specialty pharmacies.

Shortage Update for 2026

As of early 2026, Pegasys is in an active FDA drug shortage. Supply is limited and difficult to find at most retail pharmacies. See our Pegasys shortage update for the full story, or use medfinder to search pharmacies near you that have it in stock.