How much does tirzepatide reduce HbA1c, and what does that mean for you?

The SURPASS trials: where the HbA1c evidence comes from

The most detailed picture of tirzepatide's effect on HbA1c comes from the SURPASS clinical programme, a series of phase 3 trials enrolling adults with type 2 diabetes across different treatment backgrounds. SURPASS-2 compared tirzepatide directly against semaglutide 1mg and found that all three tirzepatide doses (5mg, 10mg, 15mg weekly) produced greater average reductions in HbA1c. The 15mg arm achieved a mean fall of around 2.4 percentage points from baseline. To put that in context, many people with type 2 diabetes aim for an HbA1c below 48 mmol/mol (6.5%), and a two-percentage-point drop can shift someone meaningfully closer to that range. SURPASS-1, which compared tirzepatide against a placebo in people managed by diet and exercise alone, showed reductions of 1.87–2.07 percentage points depending on dose. These are large effects by the standards of glucose-lowering treatment, and they were consistent across the programme. You can read more about how tirzepatide works at the receptor level on our tirzepatide mechanism of action page.

Why tirzepatide's dual-receptor activity matters for HbA1c

There is a common assumption that tirzepatide is simply a stronger version of a GLP-1 medicine. It is worth letting that idea go, because the distinction is clinically significant. Tirzepatide activates both the GIP receptor and the GLP-1 receptor simultaneously, the only licensed medicine in the UK to do this. GLP-1 stimulation increases insulin release in response to meals and slows gastric emptying, both of which lower post-meal glucose. GIP stimulation adds a complementary layer: it enhances insulin secretion through a separate pathway and may also reduce glucagon in a glucose-dependent way, meaning it acts mainly when blood sugar is actually elevated rather than continuously. The result is broader coverage of the glucose-spiking that drives HbA1c upward. This dual action is also one reason the research into tirzepatide's effects beyond glucose, including markers of inflammation, has attracted interest, though those benefits are still being characterised. The duration of tirzepatide's action (a half-life of around five days) also contributes to the smooth weekly coverage that the trial results reflect.

HbA1c reduction and weight loss: a connected outcome

It is difficult to fully separate tirzepatide's HbA1c effect from its effect on body weight, and the trials did not try to. Significant weight loss independently improves insulin sensitivity and lowers blood glucose, which means the two outcomes reinforce each other. In SURMOUNT-2, which recruited adults with obesity and type 2 diabetes, tirzepatide produced both substantial weight loss and meaningful HbA1c reductions, with 96% of participants at the 15mg dose reaching an HbA1c below 53 mmol/mol (7%) by week 72. This matters for anyone who has been told their blood glucose control would improve if they lost weight: tirzepatide addresses both sides of that equation at once, rather than asking patients to manage them separately. NICE's appraisal of tirzepatide (TA1026) considered this combined evidence base when making its recommendation. For a broader overview of tirzepatide's licensed uses and eligibility, our tirzepatide overview covers the full picture. Those thinking about the cost side of private treatment can find a factual breakdown on our Mounjaro price comparison page.

What this evidence means in practice

HbA1c is an average, it reflects roughly three months of blood glucose levels, which is why it takes time for any treatment to move it. Tirzepatide's trial results were measured at 40 to 72 weeks, so patience is part of the picture. The NHS patient information for tirzepatide, available via the NHS medicines page for tirzepatide, sets out what to expect in the weeks after starting. Individual results depend on starting HbA1c, dose reached, diet, activity, and other medicines already in use. A prescriber will review all of this before recommending whether tirzepatide is appropriate and, if so, at what starting point. The evidence is genuinely impressive, but it describes a population average across thousands of trial participants, not a guaranteed personal outcome. If you would like to explore whether treatment could be right for your situation, our prescribers are available to review your details. Speak to our prescribers through a free consultation, and a GPhC-registered Independent Prescriber will personally assess your case the same day.