Tirzepatide vs semaglutide: head-to-head trials for Guyana doctors

Why the comparison matters in Guyana

Physicians in Guyana are being asked about both drugs. In April 2026 President Irfaan Ali flagged the rising use of tirzepatide (Mounjaro), saying it is effective for its intended purpose while warning about off-label cosmetic use⁷. In May 2026 Health Minister Dr Frank Anthony said a manufacturer of Ozempic (semaglutide) had applied to register it, adding: "This is not a non-prescription item; you have to get a prescription"⁸. In 2024 the Government Analyst – Food and Drug Department (GA-FDD) had warned that Ozempic "is not registered here"⁹. The clinical question patients bring is simple: which one works better? Two randomized trials answer it directly.

SURPASS-2: type 2 diabetes

SURPASS-2 randomized 1,879 adults with type 2 diabetes to tirzepatide 5, 10 or 15 mg or semaglutide 1 mg once weekly for 40 weeks¹. HbA1c fell by 2.01, 2.24 and 2.30 percentage points with the three tirzepatide doses against 1.86 with semaglutide; every tirzepatide dose was noninferior and superior¹. Weight loss was also greater, by 1.9, 3.6 and 5.5 kg more than with semaglutide¹. Gastrointestinal events were the most common adverse effects in both groups and hypoglycaemia was uncommon¹. One limit matters: the comparator was semaglutide 1 mg, not the higher doses used later for diabetes or obesity.

SURMOUNT-5: obesity without diabetes

SURMOUNT-5 randomized 751 adults with obesity but no diabetes to the maximum tolerated dose of tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg) for 72 weeks². Mean weight change was −20.2 % with tirzepatide and −13.7 % with semaglutide, and waist circumference fell by 18.4 cm versus 13.0 cm². More participants on tirzepatide reached each threshold of 10, 15, 20 and 25 % weight loss². Gastrointestinal effects were again the most common, mostly mild to moderate and concentrated in dose escalation².

The placebo-controlled programmes point the same way. In STEP 1, semaglutide 2.4 mg produced a mean 14.9 % weight loss at 68 weeks against 2.4 % with placebo³. In SURMOUNT-1, tirzepatide produced 15.0 %, 19.5 % and 20.9 % at 72 weeks with 5, 10 and 15 mg, against 3.1 %⁴. In people with type 2 diabetes, the setting most relevant to Guyana's clinics, weight loss is smaller: in SURMOUNT-2 it was 12.8 % and 14.7 % with tirzepatide 10 and 15 mg against 3.2 % with placebo⁵.

Where the evidence stops

Weight and HbA1c are not the only outcomes. Semaglutide has a completed cardiovascular outcome trial in people with overweight or obesity and established cardiovascular disease but no diabetes: in SELECT, major adverse cardiovascular events fell by 20 % (hazard ratio 0.80)⁶. The two head-to-head trials were open-label and funded by the maker of tirzepatide¹², and neither was powered for hard outcomes. Neither enrolled a population resembling Guyana's specifically, and no trial has compared the two drugs in the Caribbean.

Mapping the evidence onto Guyana

The local burden is large. Guyana's 2016 Pan American STEPS survey found 23.6 % of adults aged 18–69 obese, 61.8 % of women at a BMI of 25 or more, and 11.5 % with raised blood sugar or on diabetes medication¹⁰. A nationally representative analysis of the same survey put diabetes prevalence at 18.1 %, and 24.1 % among rural women¹¹. In 2024 the chair of the Presidential NCD Commission wrote that in 2023 the Commission had urged the public sector to consider introducing GLP-1s and SGLT-2 inhibitors, while conceding "These are expensive medicines"¹². WHO added semaglutide, dulaglutide, liraglutide and tirzepatide to its Essential Medicines List in 2025 for adults with type 2 diabetes plus cardiovascular or chronic kidney disease and obesity, warning that high prices limit access¹³.

Legally, the choice is narrower than the evidence. Guyana's Food and Drugs Act, Chapter 34:03, bars advertising any drug to the public as a treatment for diabetes or obesity, both listed in its First Schedule, except as the regulations allow¹⁴, and in 2024 the GA-FDD said that Ozempic, being unregistered, should not be marketed for sale locally⁹. A trial result does not make an unregistered pen legal, and the President's concern was precisely that demand was outpacing oversight⁷.