UK regulator authorizes Mounjaro for weight loss, giving tirzepatide two brand names

Britain's Medicines and Healthcare products Regulatory Agency authorized Mounjaro (tirzepatide) for weight loss and weight management in adults on November 8, 2023, a new use for a medicine that until then was prescribed in the UK for type 2 diabetes ^[1]. Reuters reported that US regulators cleared the same drug for weight loss hours later under the brand name Zepbound ^[2].

The UK authorization covers people 18 and older with a body mass index of 30 kg/m² or above, or a BMI between 27 and 30 kg/m² alongside at least one weight-related condition, including prediabetes, high blood pressure, high cholesterol or heart problems ^[1]. The label calls for the drug to be used with a lower-calorie diet and more physical activity ^[1][2]. The decision came through the agency's national application route and was granted to Eli Lilly Nederland B.V. ^[1][3].

Mounjaro for weight management is supplied as a pre-filled injection pen in six strengths, from 2.5 mg to 15 mg of tirzepatide, injected under the skin of the abdomen, thigh or upper arm ^[1][3]. The authorized schedule begins at 2.5 mg once weekly for four weeks, then 5 mg once weekly, with any further increases spaced at least four weeks apart and capped at 15 mg weekly when a doctor recommends them ^[1]. Tirzepatide curbs appetite, the agency said, so patients feel full and report less hunger and fewer food cravings ^[1][3].

The MHRA also flagged an interaction with birth control pills. Women using oral contraceptives should consider adding a barrier method such as condoms, or switching to a non-oral form, for four weeks after their first dose and again for four weeks after each dose increase, because Mounjaro may reduce how well the pill works ^[1].

"We have prioritised rapid assessment of this new indication for Mounjaro, given the public health importance of access to new medicines to help tackle obesity," said Julian Beach, the MHRA's interim executive director for healthcare quality and access ^[1][3]. He said the agency drew on advice from the independent Commission on Human Medicines and "will keep the safety of Mounjaro under close review" ^[1][2].

Two randomized, double-blind, placebo-controlled trials, SURMOUNT-1 and SURMOUNT-2, supported the decision ^[1]. In SURMOUNT-1, 2,539 adults who were obese or overweight with at least one weight-related complication other than diabetes received weekly 5 mg, 10 mg or 15 mg of tirzepatide or a placebo for 72 weeks. Average weight change was -16.0% at 5 mg, -21.4% at 10 mg and -22.5% at 15 mg, against -2.4% for placebo; the share of patients losing at least 5% of body weight was 89.4%, 96.2% and 96.3%, versus 27.9% on placebo ^[1].

SURMOUNT-2 enrolled 938 adults who were obese or overweight and had type 2 diabetes, giving them weekly 10 mg or 15 mg of tirzepatide or placebo for 72 weeks. Mean weight change was -13.4% and -15.7%, compared with -3.3% for placebo, and 81.6% and 86.4% of treated patients lost at least 5% of body weight against 30.6% on placebo ^[1].

Nausea, diarrhea, vomiting and constipation were listed as the most common side effects, with the agency noting that vomiting usually eases over time. Low blood sugar is also very common among patients with diabetes and can appear as headache, drowsiness, weakness, dizziness, hunger, confusion, irritability, a fast heartbeat or sweating ^[1].

Why it matters for patients

Tirzepatide now sits behind two different names depending on where a reader looks. Reuters describes the US clearance as being for Zepbound ^[2], while the approval described here is for Mounjaro ^[1]. British articles about "Mounjaro for weight loss" are therefore describing a label that does not match any US product name. When coverage of this drug crosses the Atlantic, the brand name is the fastest clue to which regulator, which label and which eligibility rules are under discussion.

The trial results belong to the molecule rather than to either country's paperwork. The BMI cutoffs, weekly titration schedule and contraceptive warning summarized here come from the UK authorization ^[1]. The US approval reported by Reuters did not include that label's eligibility criteria or dosing ^[2].

The two decisions also landed the same day, which makes the naming gap easy to miss: a reader who searches for one brand can land on news about the other ^[1][2].

What happens next

The MHRA said the Summary of Product Characteristics and Patient Information leaflet would be posted on the MHRA Products website within seven days of the November 8 authorization ^[1]. The agency said it will keep the safety and effectiveness of Mounjaro under review and pointed anyone who suspects a side effect to the Yellow Card reporting scheme ^[1]. Whether the drug will be available on the NHS for weight management, when UK pharmacies will stock it for that use, and what it will cost have not been disclosed ^[1].