Several classes of diabetes medications lower A1c, with reductions ranging from about 0.5% to over 2% depending on the drug, the dose, and whether it’s used alone or in combination. The right choice depends on your starting A1c, other health conditions, and how your body responds. Here’s what each major medication class does and how much A1c lowering you can realistically expect.
Metformin: The Usual Starting Point
Metformin remains the first medication most people with type 2 diabetes are prescribed. It works three ways: it reduces the amount of glucose your liver releases into your blood, slows glucose absorption from food, and helps your cells use insulin more effectively. On its own, metformin typically lowers A1c by about 0.7% to 1.0%, depending on the dose. At 2,000 mg daily, clinical trials showed an average reduction of roughly 1%.
When paired with insulin, the effect is amplified. In one study, people taking metformin plus insulin saw their A1c drop by 2.1%, compared to 1.56% with insulin alone. Metformin is generally well tolerated, doesn’t cause weight gain, and costs very little as a generic. Its main downside is gastrointestinal side effects like nausea and diarrhea, which often ease after the first few weeks or with extended-release versions.
GLP-1 and Dual Agonists: The Strongest Newer Options
Injectable medications that mimic gut hormones have become some of the most powerful A1c-lowering drugs available. These work by stimulating insulin release when blood sugar is high, slowing stomach emptying, and reducing appetite.
Semaglutide (the active ingredient in Ozempic) lowers A1c by about 1.8% on average. Tirzepatide (Mounjaro), which targets two gut hormones instead of one, goes further. In the largest head-to-head trial, tirzepatide at its highest dose reduced A1c by 2.46%, compared to 1.86% for semaglutide. Even the lowest dose of tirzepatide outperformed semaglutide at 2.09%. Both medications also cause significant weight loss, which itself improves blood sugar control over time. Tirzepatide at the highest dose led to an average weight loss of about 27 pounds.
The most common side effects are nausea, vomiting, and diarrhea, which tend to be worst in the first weeks and improve as your body adjusts. These medications are typically started at a low dose and gradually increased for that reason.
SGLT2 Inhibitors: Blood Sugar Plus Heart and Kidney Protection
SGLT2 inhibitors work through an entirely different mechanism. They block your kidneys from reabsorbing glucose, so excess sugar leaves your body through urine. Common examples include empagliflozin, dapagliflozin, and canagliflozin. As standalone therapy, they lower A1c by roughly 0.5% to 0.8%. Combined with metformin from the start, reductions reach 1.8% to 2.1%.
What sets this class apart is the benefits beyond blood sugar. Clinical trials have shown they improve cardiovascular outcomes and protect kidney function in people with type 2 diabetes. They also lower blood pressure by about 3 to 4 points systolic and promote modest weight loss. The trade-off is an increased risk of urinary tract infections and yeast infections, since more sugar is passing through the urinary tract. Dehydration can also be a concern, especially in older adults or people on blood pressure medications.
DPP-4 Inhibitors: Modest but Gentle
DPP-4 inhibitors like sitagliptin (Januvia) work by extending the life of natural gut hormones that stimulate insulin release. They’re taken as a daily pill, which appeals to people who prefer not to inject. The downside is potency: as monotherapy, they lower A1c by only about 0.5% to 0.8%. Added to metformin, the reduction improves to around 0.9%.
Their main advantage is that they’re weight-neutral and cause very few side effects. They don’t cause the nausea associated with GLP-1 drugs or the infection risk of SGLT2 inhibitors. However, if you’re already on a GLP-1 medication, adding a DPP-4 inhibitor provides no additional glucose lowering, since they work on overlapping pathways. Current guidelines specifically recommend against using both together.
Sulfonylureas: Effective but With Trade-offs
Sulfonylureas (glipizide, glimepiride, glyburide) have been used for decades. They stimulate your pancreas to release more insulin regardless of your blood sugar level, which is both their strength and their weakness. They lower A1c by 1.5% to 2%, making them among the more potent oral options. They’re also inexpensive generics.
The problem is that forcing insulin release when blood sugar is already normal can cause hypoglycemia, which happens in 2% to 4% of patients per year. Low blood sugar episodes can cause shakiness, confusion, and in severe cases, loss of consciousness. Sulfonylureas also tend to cause weight gain. For these reasons, they’ve fallen behind newer drug classes in treatment guidelines, though they remain a reasonable option when cost is a major barrier.
Thiazolidinediones: A Niche Role
Pioglitazone is the main drug still used in this class. It makes your fat and muscle cells more responsive to insulin. A large review found it lowers A1c by about 0.8% compared to placebo. Recent guidelines have given it a renewed role for people who have both type 2 diabetes and fatty liver disease, where it can address both conditions simultaneously.
The concerns are real, though. Pioglitazone causes fluid retention, which leads to edema and weight gain. More seriously, it increases the risk of heart failure, particularly in people who already have heart problems. It has also been linked to reduced bone density, raising fracture risk. These side effects limit its use to specific clinical situations.
Insulin
Insulin is the most flexible A1c-lowering tool because there’s no ceiling on its effect. The dose can always be increased to match your body’s needs. It’s essential for type 1 diabetes and becomes necessary for many people with type 2 diabetes as the disease progresses and the pancreas produces less insulin on its own. When added to metformin, the combination can lower A1c by over 2%. The downsides are daily injections, the need for blood sugar monitoring, risk of hypoglycemia, and weight gain.
How Combination Therapy Works
Most people with type 2 diabetes eventually need more than one medication. Because each class lowers blood sugar through a different mechanism, combining them produces additive effects. Starting two drugs together typically reduces A1c by 1.0% to 2.0%, with some triple combinations reaching 2.5% or more. In one trial, starting metformin, pioglitazone, and a GLP-1 drug simultaneously lowered A1c by 2.6%.
The approach your doctor takes depends largely on your A1c at diagnosis. If it’s only modestly elevated, metformin alone may be enough. If it’s significantly above target, starting with two medications simultaneously gets you to goal faster, which matters because prolonged high blood sugar increases the risk of complications in the eyes, kidneys, and nerves.
How Quickly Medications Affect A1c
A1c reflects your average blood sugar over the past two to three months, so don’t expect dramatic changes at your first follow-up if you started medication recently. Most clinical trials measure A1c changes at 24 weeks (about six months), which gives a reliable picture of a medication’s full effect. Your doctor will typically recheck your A1c three months after starting or changing a medication. If results aren’t on target, that’s usually when a dose adjustment or second medication gets added.