FOI release

Levothyroxine monotherapy

Some or all of the information requested was not provided because we didn't hold it.

Case reference FOI2026/00499

Received 7 May 2026

Published 5 June 2026

Request

Dear MHRA FOI Team, Thank you for your response of 6 May 2026, stating that the MHRA does not hold information regarding the scientific evidence review or rationale that justifies Levothyroxine monotherapy as the UK’s 'first choice' or the standard treatment. I find this admission concerning from a statutory perspective. Under the Human Medicines Regulations, the MHRA is the designated body responsible for the safety, quality, and efficacy of medicines in the UK. If the MHRA does not hold the scientific rationale for the efficacy of the UK’s third most-prescribed drug, I request a formal clarification on the following: 1. Statutory: How does the MHRA fulfill its duty to ensure the ongoing efficacy of Levothyroxine monotherapy if it holds no internal scientific review of the biological mechanisms (specifically deiodination/conversion) that justify its licence? 2. Regulatory: In a concurrent response (Ref: CEO 20584), the MHRA CEO’s office states that the product’s efficacy is predicated on conversion to the active ligand. If the FOI team holds no records of this rationale, does this indicate that the MHRA is relying entirely on third-party guidelines (e.g., NICE, BTA, and SfE)—none of which account for the mechanisms of deiodinases or conversion—rather than conducting its own independent regulatory due diligence? 3. Information Not Held: If the MHRA enforces manufacturing standards for this drug but does not hold the scientific rationale for its biological 'Action and Use,' at what point did the MHRA decouple manufacturing oversight from biological efficacy? I wish to register this as a formal challenge to the adequacy of the search. It is implausible that a statutory regulator holds no record of the scientific basis for the primary treatment of a condition affecting millions.

Response

See attached

Documents

• FOI2026_00499 (redacted).pdf (751.7 KB)

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