By the PharmaTradz BD Team. Published November 2026.
Every generic medicine starts with a purchase that has nothing generic about it: a few hundred packs of the originator product, bought in the right country, with the right paperwork, at the right time. Get the reference product wrong and a bioequivalence study can be rejected, a dossier delayed by a year, or a development budget spent twice.
This guide is for formulation scientists, regulatory teams, CROs and procurement managers who buy reference listed drugs (RLDs), reference medicinal products (RMPs) and comparators for development, bioequivalence and clinical studies. It covers what regulators expect, the documents you need, and how to avoid the most common sourcing problems.
RLD, RMP, comparator: what each regulator expects
The names differ, but the principle is the same: the generic must be compared with the product the regulator accepts as the benchmark.
- United States. FDA designates a Reference Listed Drug and, for testing, a Reference Standard in the Orange Book. The study must use the US product.
- European Union. The comparison is normally with a Reference Medicinal Product authorised in the EU or EEA. A product bought in one member state can generally serve for filings across the EU, but the exact country of purchase and the authorisation behind it must be documented.
- WHO and many other markets. WHO guidance recommends the innovator product available on the market as the logical comparator, and WHO publishes a list of international comparator products for prequalification. Several national regulators require or prefer the locally registered innovator, or accept a foreign comparator only with justification or a bridging study.
Before buying anything, write down every market where the dossier will be filed and confirm which comparator each one accepts. One well-chosen purchase can often support several filings; the wrong one supports none.
The documents that make a reference product usable
Regulators do not just ask what you compared against; they ask how you can prove it. Keep a complete chain of custody:
- Purchase invoice from a licensed wholesaler or pharmacy in the reference country, showing product name, strength, pack, batch number and expiry;
- Photographs or scans of packs and labels from the batches used;
- Shipping records, including temperature data for cold-chain products;
- Import permits or test licences where your country requires them for unregistered reference products;
- A certificate of analysis or your own testing of potency and dissolution before the study. WHO guidance expects the assay of test and comparator to be close and within about 5% of each other.
How much to buy
Teams often under-order, then cannot find the same batch again. Plan quantities for:
- Characterisation and dissolution profiling during development;
- Pilot and pivotal BE studies, including spare units for dropouts and repeats;
- Retention samples. FDA rules require reserve samples of test and reference products. Revised FDA guidance in 2024 reduced the recommended minimum for in vivo studies to 30 single-dose or 3 multi-dose units of each, across all sites, instead of five times the testing quantity;
- Stability comparisons and any later bridging work.
Wherever possible, buy enough from a single batch with a long remaining shelf life. Mixing batches complicates the analysis, and a comparator that expires halfway through a study is a costly surprise.
Common sourcing problems, and how to avoid them
- Restricted distribution. Some originators supply only through specialty channels or limit quantities per buyer. Start early and use suppliers with established wholesaler relationships in the reference country.
- Parallel or relabelled packs. A pack relabelled for another market may not count as the reference product. Ask for country-of-origin packs and check the authorisation number.
- Short expiry. Specify a minimum remaining shelf life in the order, for example 12 months at delivery.
- Cold chain and controlled substances. Biologics, peptides and scheduled drugs need validated shipping and the right export and import permits. Allow extra time.
- Price. Originator products are expensive and prices vary by country. Compare offers from several reference markets where regulators allow it, but never trade documentation for a lower price.
- Counterfeits and grey market. Buy only through licensed channels with full traceability. A cheap pack with no invoice is worthless to a regulator.
Beyond the RLD: other critical purchases for development
The same sourcing discipline applies to reference standards and impurity standards, innovator APIs for characterisation, functional excipients, primary packaging and placebo materials for clinical trials. All of them need traceable origin and documents that will survive an audit.
How PharmaTradz helps
We source innovator and reference products from licensed wholesalers in the US, EU, UK and other reference markets, with invoices, batch details and cold-chain records where needed. Send us the product, strength, reference country, quantity and the markets you will file in, and we will confirm availability, batch and expiry before you commit.
- Innovator drug and comparator sourcing
- Send your reference product requirement
- Looking for a development or manufacturing partner for the generic itself? Browse CDMO capacity.
The bottom line
The reference product is a small line in a development budget and a large risk in a dossier. Decide the target markets first, buy from licensed channels in the right country, keep every document, and order enough from one batch to finish the job.
This article is general business information, not regulatory advice. Comparator requirements differ by country and change over time; confirm them with each regulator before purchase.
Frequently Asked Questions(FAQs)
What is a reference listed drug (RLD)?
The approved originator product that FDA designates as the benchmark for generic applications in the United States. Europe uses the term reference medicinal product, and WHO and other regulators often use "comparator".
Can I use an EU reference product for a US filing?
Generally no. FDA expects bioequivalence against the US reference standard listed in the Orange Book. Europe likewise expects an EU or EEA authorised reference product.
Which documents prove the origin of a comparator?
A purchase invoice from a licensed source in the reference country showing batch and expiry, pack photographs, shipping and temperature records, any import permits, and your own potency and dissolution testing.
How many retention samples are needed for a US bioequivalence study?
Revised FDA guidance in 2024 recommends at least 30 single-dose or 3 multi-dose units of each of the test and reference products for in vivo studies, across all testing sites.
How long does reference product sourcing take?
Common products can often be supplied within a few weeks. Restricted-distribution, cold-chain and controlled products can take longer, so plan purchases at the start of development.
