Interchangeable biosimilar status and pharmacy substitution
An interchangeable biosimilar may be substituted for its reference product at a US pharmacy, subject to state law. It is not a safety ranking.
An interchangeable biosimilar is an FDA-approved biosimilar that may be substituted for its reference product at a pharmacy without the prescribing health care professional's intervention, subject to state law. The designation does not mean it is safer or more effective than a biosimilar without interchangeable status. FDA explains both points on its biosimilar information page.
For a dispensing decision, split the checks. Confirm the product's FDA interchangeable biosimilar designation, then apply the state pharmacy rule for that prescription. The designation alone does not settle cost, a prescriber block or patient notice.
Biosimilar versus interchangeable biosimilar
A biosimilar is highly similar to its FDA-approved reference product. It has no clinically meaningful differences in safety, purity or potency, meaning safety and effectiveness. Manufacturers specifically request interchangeable approval. Absence of that designation does not mean the biosimilar is clinically inferior. These distinctions come from FDA's explanation of biosimilars and interchangeable products.
FDA calls it a common misconception that additional statutory requirements make an interchangeable biosimilar safer or more effective than one without the designation. Both can be used in place of the reference product and are considered as safe and effective as that product. FDA says accumulated experience indicates that biosimilars and interchangeable biosimilars have the same safety and effectiveness. On the same FDA page, that wording is about clinical use, not pharmacy substitution. The practical difference is the substitution pathway.
| Question | Biosimilar without interchangeable status | Interchangeable biosimilar |
|---|---|---|
| Is it highly similar to its reference product, without clinically meaningful differences? | Yes | Yes |
| Does this status permit substitution without prescriber intervention, subject to state law? | No | Yes |
| Does interchangeable status mean greater safety or effectiveness than other biosimilars? | Not applicable | No |
Source: FDA's explanation of the two approval categories.
Which biosimilars are interchangeable?
One confirmed example is Wezlana (ustekinumab-auub). On 31 October 2023, FDA announced its approval as biosimilar to and interchangeable with Stelara (ustekinumab). That announcement is one FDA-approved interchangeable biosimilar example. It is not a complete current list. See the FDA Wezlana approval announcement.
For a current check, use the FDA Purple Book. FDA directs readers there for licensed biosimilar and interchangeable products on its Biosimilar Product Information page. A general biosimilar approval list is not an interchangeable-only list. That gap shows up when a table gets pasted into a tracker. Before you rely on a row for substitution, work through the record:
- Match the brand and proper name to the official record.
- Confirm the reference product named in that record.
- Check the strength and presentation for the supply you actually intend to dispense.
- Confirm interchangeable status. Do not infer it from biosimilar approval.
Products that share a molecule are not automatically substitutable for one another. Keep the reference product in the result. A dated approval announcement is evidence of what FDA announced that day. It is not the record for a particular pack on the day you dispense.
If the tracker has one date column, split it. Store the reference product, the original biosimilar approval and the interchangeable status separately, with the source link and the date of the check. Where the record shows only biosimilar approval, write that, and leave interchangeability blank.
Humira biosimilar interchangeability and insulin checks
Humira and insulin searches start with the named product. FDA's product-information table, content current 28 October 2026, pairs Cyltezo (adalimumab-adbm) with Humira and Semglee (insulin glargine-yfgn) with Lantus. The original biosimilar approval months shown are August 2017 and July 2021. Those months are not interchangeable-designation dates. Don't copy Cyltezo's August 2017 approval into an interchangeability field.
For the first interchangeable biosimilar insulin, that same table links Semglee to an announcement titled "FDA Approves First Interchangeable Biosimilar Insulin Product for Treatment of Diabetes." The title does not give an exact approval day. July 2021 is the biosimilar approval month in the table, not a designation date. The title also does not replace a Purple Book product check of the strength and presentation before a current dispensing decision.
Can pharmacists substitute automatically?
Substitution is not automatic.
Interchangeable status permits substitution without intervention from the prescribing health care professional, depending on state pharmacy law. It does not create one national dispensing rule. FDA states this boundary directly.
California is one reason the statute still matters. Business and Professions Code section 4073.5 lets a pharmacist select an interchangeable alternative only if the prescriber has not prohibited substitution. Selection stays inside the pharmacist's discretion. The substitution must be communicated to the patient. The cost to the patient must be the same or less, and that cost includes any professional fee the pharmacist charges. These are California conditions, not a national checklist.
The same section generally requires, within five days after dispensing, an entry of the product name and manufacturer in a record the prescriber can access electronically. Alternatives and exceptions sit in the section, so read it before you turn the example into a procedure. The law also leaves prior authorization and other appropriate utilization controls in place. Interchangeable status does not guarantee coverage, and it does not require the pharmacist to substitute.
On the compliance file, keep the FDA-status check and the state-law check on separate lines. A designation shows the product may be substituted without prescriber intervention, subject to state law. It does not show that California's five-day entry, cost test and patient communication, or another state's conditions, have already been met.
Does FDA still require switching studies?
FDA says it now generally does not recommend switching studies. The 29 October 2025 announcement on biosimilar development states that position expressly. Don't turn "generally" into a prohibition, or into a promise that a switching study can never be asked for.
The June 2024 FDA guidance on biosimilar interchangeability is a different document. It is labelled Draft Level 1 Guidance and "Not for implementation." It gives nonbinding recommendations, including an assessment of how comparative analytical and clinical data support the statutory switching standard. See the FDA interchangeability draft guidance record. A recommendation in that draft is not a binding requirement.
FDA's educational page, updated 26 October 2026, still says the updated recommendations apply "when finalized." The current FDA explanation separates that policy sentence from the draft's status.
The 2025 announcement also discusses comparative efficacy studies. Those are not switching studies, so don't merge them in a development note. The FDA announcement treats them as separate subjects. A change in recommended evidence does not, by itself, mean the interchangeable designation has ended or that a statute has repealed its requirements. Check the product. The announcement is not permission to substitute in every state.
How biosimilar interchangeability differs in the UK
The interchangeability of biosimilars does not carry the US pharmacy effect in the UK. MHRA considers an authorised biosimilar interchangeable with its reference product and with another biosimilar to the same reference. Switching decisions rest with the prescriber in consultation with the patient, following shared decision-making principles. See section 10 of MHRA's guidance on licensing biosimilar products.
RegAffairs AI answers this question in its interchangeable biosimilar explanation. Do not reuse a US substitution sentence as a UK dispensing instruction. Section 11 of the same MHRA guidance states that pharmacy-level substitution without consulting the prescriber is not permitted for biological medicines, including biosimilars.