New-to-Brand Prescriptions (NBRx)

Key facts

What it counts

Patients starting a brand, not total prescriptions

Requires

Patient-level longitudinal prescription data, usually de-identified

Lookback window

Defined by each data source; lengths differ

Typical components

New to market, switches, add-ons and, in some sources, restarts

What are new-to-brand prescriptions?

NBRx answers a question that total prescriptions (TRx) and new prescriptions (NRx) cannot: how many patients are starting a product. A patient counts as new to brand when a prescription for the brand is dispensed and no prescription for it appears in that patient's history during a defined lookback window.

Because the measure depends on each patient's prior history, NBRx requires longitudinal data that links prescriptions for the same patient over time. In practice this means de-identified or tokenized pharmacy and medical claims rather than simple pharmacy-level dispensing counts.

How NBRx is broken down

Analysts often split NBRx by where the patient came from:

Vendors differ on lookback length, on whether restarts count and on whether the market is defined at the molecule, brand or class level. NBRx figures from two sources are rarely directly comparable.

• New to market, or new therapy starts: patients with no prior treatment in the drug class during the lookback.
• Switches: patients who stopped a competing product and started the brand.
• Add-ons: patients who started the brand while continuing another therapy.
• Restarts: patients returning to the brand after a gap longer than the lookback, which some vendors count as NBRx and others exclude.

Why NBRx matters

NBRx is usually the most closely watched launch metric. Patient starts are a leading indicator of future volume, while TRx lags as patients accumulate refills. NBRx share within a class shows whether a new entrant is winning the patients whose treatment decisions are being made now.

Switch-source analysis shows which competitors a brand is taking patients from, which informs messaging, contracting and competitive intelligence. Market access teams compare NBRx across payer segments to see where formulary restrictions or prior authorization are slowing starts.

NBRx vs NRx

A long-term patient who receives a fresh prescription when refills run out generates an NRx but not an NBRx. A patient who switches from a competitor generates both. As a result, NBRx is lower than NRx and moves more sharply when prescriber behavior changes.