By the PharmaTradz BD Team. Published October 2026.
Comparator sourcing is the buying of commercially marketed medicines for use in clinical research: as the active control arm in a clinical trial, or as the reference product in a bioequivalence study. A comparator is the established treatment or placebo that a new medicine is measured against. The hard part is not the purchase but proving where each pack came from, keeping it in the right conditions and securing enough of one batch, with enough shelf life, when the trial needs it.
What a comparator is, and why trials need one
Many trials compare a new medicine with the treatment patients would otherwise receive, the standard of care, to show whether it is better, no worse or simply different. That active control is the comparator. The EU Clinical Trials Regulation (Regulation (EU) No 536/2014, or CTR) reflects this in its definition of an investigational medicinal product (IMP): a medicinal product "being tested or used as a reference, including as a placebo, in a clinical trial". In other words, once a marketed medicine is used as a comparator, it is an IMP for that trial.
Generic and biosimilar developers need comparators for a second reason. To show that a generic tablet behaves like the original, they run a bioequivalence (BE) study, usually in healthy volunteers, comparing blood levels after the generic and after the original brand. The original brand used in that study must be the exact product the regulator names, sourced from the right market.
RLD, reference standard and reference medicinal product
The terms differ between regulators, and mixing them up wastes money.
| Term | Where it is used | What it means |
|---|---|---|
| Reference listed drug (RLD) | US, generic applications (ANDAs) | The listed drug identified by FDA that a generic applicant relies on to seek approval (21 CFR 314.3). Shown in a separate RLD column in the Orange Book. |
| Reference standard | US, generic applications | The product FDA selects for the applicant to use in its in vivo BE study. Usually the RLD, but not always. |
| Reference product | US, biosimilars | The single licensed biological product a proposed biosimilar is compared against, listed in FDA's Purple Book. |
| Reference medicinal product | EU, generic applications | A product authorised in the EU under Article 6 of Directive 2001/83/EC, in line with Article 8, to which a generic is shown to be bioequivalent (Article 10). |
| Comparator | Clinical trials everywhere | The active control or placebo used as a reference in a trial. Under the CTR it is an investigational medicinal product. |
The US distinction matters most when the original brand has left the market. FDA's 2020 guidance Referencing Approved Drug Products in ANDA Submissions explains that the reference standard "may or may not be the same listed drug as the RLD". If the RLD is discontinued, FDA generally names a previously approved generic as the reference standard, and it may change the reference standard to deal with shortages. Check the Orange Book when you place the order, not only when you write the protocol.
In the EU, the reference medicinal product can be authorised in a different member state from the one where the generic is filed (Article 10(1) of Directive 2001/83/EC). EMA's Guideline on the Investigation of Bioequivalence adds that the batch used in the BE study should belong to the global marketing authorisation of that reference product, and that the test and reference batches should normally differ in assayed content by no more than 5%. In the UK, MHRA guidance on comparators in BE studies (updated December 2024) generally expects a UK-sourced comparator, but accepts one authorised in and sourced from the EU/EEA, Switzerland, the USA, Canada, Australia, Japan or Singapore if it is shown to be representative of the UK product.
Sourcing routes
There are two lawful ways to buy a comparator.
Direct from the marketing authorisation holder. The company that owns the product sells to the sponsor, sometimes under a supply agreement. This gives the cleanest documentation, often including a batch-specific certificate of analysis and storage data. It can take longer, and the holder may limit quantities or decline to supply a rival's trial.
Through licensed wholesalers and specialist comparator distributors. Most comparators are bought this way. A wholesaler holding a wholesale dealer's licence in the EU or UK, or a state wholesale distributor licence in the US, buys from the authorisation holder or its appointed distributors and sells on to the sponsor or its clinical supply vendor. Done properly, this route is fully traceable; done badly, it is where falsified or poorly stored stock enters.
Either way, the comparator must come from the market the protocol or regulator requires. The same medicine authorised elsewhere is a different product in law.
The documents you should expect
A comparator is only as good as the paperwork that travels with it. A complete pack usually includes:
- Certificate of analysis (CoA) for the batch, or at least the manufacturer's batch release information. Our guide to reading a CoA explains what to look for.
- Chain-of-custody records showing every licensed party from manufacturer to you, with invoices and licence copies. In the EU and UK this is a matter of good distribution practice (GDP); for US packs, ask for the traceability data that US trading partners exchange under the Drug Supply Chain Security Act (DSCSA).
- Country of origin and country of authorisation, batch number, expiry date and pack presentation, so you can match the product to the protocol.
- Storage and transport data: temperature records for each leg, and a statement that the stock has not been returned or relabelled.
- Where needed, the product information and photos of the pack and label.
Our explainer on good distribution practice covers GDP in detail.
Import and QP certification for EU and UK trials
Under Article 61 of the CTR, manufacturing or importing IMPs into the EU needs an authorisation and a qualified person (QP), the named expert who signs off each batch. Article 62 requires the QP to certify that each batch manufactured in or imported into the EU meets the GMP standards in Article 63, and Article 63(3) says imported IMPs must be made to standards at least equivalent to EU GMP. Article 64 adds a useful exception: for an authorised IMP, meaning a product already authorised in the EU or in a member state concerned, these articles apply only to modifications. So an EU-authorised comparator used unchanged is simpler to handle than one bought outside the EU, which must be imported and certified like any other IMP. The CTR has applied since 31 January 2022, and the transition period for older trials ended on 31 January 2025.
Great Britain works differently. Under MHRA guidance on importing IMPs from approved countries, which currently means the EU and EEA, a UK manufacturing and import authorisation (MIA(IMP)) holder runs an assurance system that checks each batch was certified by a QP in the listed country; the batch is not recertified. IMPs from other countries must be certified in the UK. The UK's new clinical trials regulations came into force on 28 April 2026, so check the current MHRA guidance before you plan a GB import. In the US, an investigational drug can be imported when an IND is in effect and the consignee is the sponsor, a named investigator or the domestic agent of a foreign sponsor (21 CFR 312.110).
Blinding and over-encapsulation
In a double-blind trial, neither patients nor investigators may know who receives which treatment. A branded tablet gives the game away, so sponsors often over-encapsulate it: they place the tablet inside an opaque capsule, sometimes with a filler, so it looks the same as the new product or a matching placebo. Alternatives include identical blinded kits or a double-dummy design with placebos for both products.
Any change to the comparator counts as manufacturing. In the EU it brings the product back within Articles 61 to 63 of the CTR, and the sponsor needs data, typically comparative dissolution and stability, showing the change does not alter how the product behaves. A repackaged comparator's use-by date must be justified and cannot run past the expiry of the original pack, which is why remaining shelf life on arrival matters so much.
Cold chain, lead times and supply risk
Many comparators, especially biologics, must be kept refrigerated or frozen. One temperature excursion can make an expensive batch unusable, so ask for continuous records and qualified packaging. Our guide to the pharmaceutical cold chain sets out the ranges and how excursions are handled.
Lead times vary widely with the product, the market and the quantity. The risks that delay trials are predictable: national shortages that divert stock to patients, authorisation holders that limit volumes, and batch splits, where a large order arrives as several batches with different expiry dates. Each extra batch adds testing, labelling and records. US rules on BE studies (21 CFR 320.38 and 320.63) also require reserve samples of both the test product and the reference standard, enough for FDA to repeat all release tests five times, kept for at least five years, so order those quantities from the same batch up front.
A worked example
A sponsor plans a 12-month, double-blind trial in Germany, Poland and Great Britain against an established oral tablet. It needs around 40,000 tablets, over-encapsulated to match a placebo. Buying an EU-authorised pack through a licensed wholesaler keeps the import simple, but over-encapsulation is a modification, so a manufacturer with an IMP authorisation must do the work and a QP must certify the finished kits. The sponsor asks for a single batch with at least 24 months of shelf life remaining on delivery, because the encapsulated product's use-by date cannot exceed the original expiry and the trial needs a margin for packaging and recruitment delays. For the British sites, a UK MIA(IMP) holder checks the EU QP certification under the assurance system before release.
What buyers should check
- Right product, right market: does the pack match the RLD, reference standard or reference medicinal product named for your study, checked against the Orange Book or the relevant authorisation on the order date?
- Licences: does every party in the chain hold a current wholesale or manufacturing licence, and will you receive copies?
- Batch and expiry: how many batches will make up the order, and what shelf life will remain on arrival?
- Documents: CoA, chain of custody, country of origin, temperature records and, for EU or UK trials, the QP route?
- Quantity: have you included BE reserve samples, testing samples and an overage for losses?
- Blinding plan: who will over-encapsulate or relabel, under which authorisation, and with what supporting data?
- Recalls and returns: how will the supplier tell you of a recall, and can unused stock be returned?
If your project involves patients outside a trial, our explainer on early access programmes covers the separate rules for supplying unapproved medicines.
How PharmaTradz can help
PharmaTradz supplies comparators and reference products to sponsors, CROs and clinical supply vendors through licensed routes, with batch documentation shared before you commit. Our comparator and clinical trial supply page explains the service. Tell us the product, strength, market of origin, quantity and required shelf life, and send us an RFQ. For other terms, see our pharma abbreviations A-Z.
Frequently Asked Questions(FAQs)
What is a comparator drug in a clinical trial?
A comparator is the established treatment or placebo that a new medicine is measured against in a trial, usually a commercially marketed product bought from the open market. Under the EU Clinical Trials Regulation it counts as an investigational medicinal product.
What is a reference listed drug (RLD)?
An RLD is the approved drug product FDA identifies as the one a generic applicant relies on when it files an abbreviated new drug application (ANDA). RLDs are flagged in a dedicated column of the Orange Book.
What is the difference between an RLD and a reference standard?
The RLD is the product a generic relies on for approval, while the reference standard is the product FDA selects for the generic's in vivo bioequivalence study. They are usually the same, but if the RLD is discontinued FDA generally names a previously approved generic as the reference standard.
Can a comparator for an EU trial be bought outside the EU?
Yes, but it must be imported by a holder of an import authorisation and each batch certified by a qualified person under Articles 61 to 63 of Regulation (EU) No 536/2014. For an EU generic bioequivalence study, the reference batch should normally belong to the EU-authorised reference medicinal product.
What is over-encapsulation of a comparator?
Over-encapsulation means placing a comparator tablet inside an opaque capsule so it looks the same as the test product or a placebo, keeping a trial blind. It counts as manufacturing, so it needs an appropriate authorisation and data, such as comparative dissolution and stability, showing the product's performance is unchanged.
