Several classes of diabetes medication can lower A1c by anywhere from 0.4% to over 2 percentage points, depending on the drug, the dose, and your starting level. The full effect of most non-insulin medications takes three to six months to show up on lab work, so your doctor will typically reassess your A1c at that point before adjusting your regimen. Understanding how each medication works and what kind of reduction it delivers can help you have a more informed conversation about your treatment plan.
Metformin: The Usual Starting Point
Metformin is the first medication most people with type 2 diabetes are prescribed, and for good reason. It works primarily by reducing the amount of glucose your liver releases into your bloodstream. Your liver constantly produces sugar between meals, and in type 2 diabetes, that process runs too high. Metformin dials it back by suppressing the genetic signals that drive sugar production in liver cells. It also modestly improves how well your muscles and fat tissue respond to insulin.
On its own, metformin typically lowers A1c by about 1 to 1.5 percentage points. It’s inexpensive, well studied over decades, and doesn’t cause low blood sugar (hypoglycemia) when used alone. The most common side effects are gastrointestinal: nausea, diarrhea, and stomach upset, which often improve after a few weeks or with an extended-release formulation. One less obvious concern is that metformin can reduce your body’s absorption of vitamin B12 over time. Each one-gram increase in your daily dose roughly doubles the risk of B12 deficiency. The American Diabetes Association recommends periodic B12 monitoring, with the prescribing information calling for blood checks every two to three years in people with risk factors.
GLP-1 Receptor Agonists
GLP-1 receptor agonists, which include semaglutide (Ozempic, Wegovy) and liraglutide (Victoza), are injectable or oral medications that mimic a gut hormone your body releases after eating. This hormone signals your pancreas to produce more insulin when blood sugar is high, slows stomach emptying so sugar enters your bloodstream more gradually, and reduces appetite.
These medications are among the most effective options available. In clinical trials, semaglutide lowered A1c by 1.0 to 1.7 percentage points from baseline. The weight loss they produce, often significant, contributes additional benefits for blood sugar control and cardiovascular health. Side effects center on the digestive system: nausea, vomiting, and diarrhea are common when starting or increasing the dose, and they tend to ease over several weeks as your body adjusts.
Dual GIP/GLP-1 Agonists: Tirzepatide
Tirzepatide (Mounjaro) is a newer medication that activates two gut hormone receptors instead of one, combining GLP-1 activity with GIP receptor stimulation. This dual action produces the largest A1c reductions seen in any non-insulin diabetes drug tested to date.
Across five large clinical trials involving over 6,000 participants, tirzepatide lowered A1c by 1.9 to 2.6 percentage points from baseline, depending on the dose. In head-to-head comparisons, even the lowest dose of tirzepatide outperformed injectable semaglutide 1 mg for A1c reduction. At the highest dose (15 mg), participants saw an average A1c drop of 2.3 percentage points compared to 1.86 for semaglutide. Weight loss was also substantial, up to 15.5 kg (about 34 pounds) more than comparators. The side effect profile is similar to GLP-1 drugs: nausea and other GI symptoms are most common during dose escalation.
SGLT2 Inhibitors
SGLT2 inhibitors, including empagliflozin (Jardiance) and dapagliflozin (Farxiga), take a completely different approach. They work through the kidneys. Normally, your kidneys filter glucose out of your blood and then reabsorb almost all of it back. SGLT2 inhibitors block part of that reabsorption process, causing excess glucose to spill into your urine.
The A1c reduction is more modest than some other drug classes, but these medications offer important benefits beyond blood sugar control. They lower blood pressure slightly through mild fluid loss, and large trials have shown meaningful protection for the heart and kidneys. They’re often added specifically for those secondary benefits in people who already have cardiovascular disease or kidney problems. Because they cause glucose to pass into the urine, the most notable side effects are an increased risk of urinary tract infections and genital yeast infections. They also don’t cause hypoglycemia on their own.
DPP-4 Inhibitors
DPP-4 inhibitors, such as sitagliptin (Januvia) and linagliptin (Tradjenta), work by extending the life of the same gut hormones that GLP-1 drugs mimic. Rather than flooding your system with a synthetic version of the hormone, they prevent the enzyme that breaks it down from doing its job. The result is a gentler boost to your body’s natural insulin response after meals.
The trade-off for that gentler mechanism is a smaller effect. In real-world studies, DPP-4 inhibitors lowered A1c by about 0.6 percentage points. When used as a second medication after metformin, their performance was similar to sulfonylureas. But in people who had already tried and failed other medications beyond metformin, DPP-4 inhibitors produced better glucose control. They’re taken as a daily pill, are generally well tolerated, and carry a low risk of hypoglycemia, making them a reasonable option when more powerful medications aren’t appropriate.
Sulfonylureas
Sulfonylureas are one of the oldest classes of diabetes medication. They stimulate your pancreas to release more insulin regardless of your blood sugar level, which is both their strength and their main drawback. They lower A1c by roughly 0.4 to 1.0 percentage points, and they’re inexpensive.
The downside is meaningful. Because they push insulin release continuously, sulfonylureas carry a higher risk of hypoglycemia (dangerously low blood sugar), especially if you skip meals or exercise more than usual. They also tend to cause weight gain. For these reasons, newer guidelines generally favor other second-line options like GLP-1 drugs or SGLT2 inhibitors, though sulfonylureas remain widely used worldwide due to their low cost and long track record.
Pioglitazone and TZDs
Pioglitazone belongs to the thiazolidinedione class. It works by making your fat, liver, and muscle cells more sensitive to insulin, addressing one of the core problems in type 2 diabetes. In studies where pioglitazone was added on top of metformin and a sulfonylurea, A1c dropped by about 0.7 to 0.8 percentage points over three to six months.
Pioglitazone has fallen out of favor as a go-to option because of side effects including fluid retention, weight gain, and an increased risk of bone fractures. It’s still used in certain situations, particularly for people with fatty liver disease, where it has shown specific benefits.
Basal Insulin
When oral medications and injectable drugs like GLP-1 agonists aren’t enough, adding basal (long-acting) insulin is often the next step. Basal insulin provides a steady, low level of insulin throughout the day and night, suppressing the liver’s sugar output between meals and overnight.
In the landmark UK Prospective Diabetes Study, adding basal insulin brought average A1c down from 9.1% to about 7.8% within a year. The magnitude of the drop depends heavily on your starting point: the higher your A1c, the larger the potential reduction. Starting insulin requires learning to use injection devices and checking blood sugar more frequently, at least initially. Hypoglycemia and weight gain are the primary concerns, though modern long-acting insulin formulations have reduced the hypoglycemia risk compared to older versions.
How Medications Are Combined
Most people with type 2 diabetes will eventually need more than one medication. The disease tends to progress over time as the pancreas gradually loses its ability to produce enough insulin. A combination approach targets blood sugar from multiple angles: metformin reduces liver sugar output, a GLP-1 drug boosts insulin response and curbs appetite, and an SGLT2 inhibitor removes excess glucose through the kidneys. Each drug addresses a different piece of the problem.
When you start a new medication or adjust a dose, expect to wait three to six months before seeing the full impact on your A1c. That’s the timeframe for non-insulin medications to reach their maximum effect. Your A1c result reflects an average of your blood sugar over the previous two to three months, so a test taken too soon after a medication change won’t capture the full benefit. If your A1c hasn’t reached your target at the three-to-six-month mark, that’s the typical point when your provider will consider adding another agent or increasing the dose.
What Lowers A1c the Most
If raw A1c reduction is the priority, the ranking from clinical trial data is fairly clear. Tirzepatide leads with reductions of up to 2.6 percentage points. GLP-1 receptor agonists like semaglutide come next at 1.0 to 1.7 points. Metformin and basal insulin each deliver roughly 1.0 to 1.5 points. Pioglitazone and DPP-4 inhibitors sit in the 0.6 to 0.8 range. SGLT2 inhibitors produce more modest A1c changes but carry significant heart and kidney benefits that may matter more than the number on your lab report.
Your actual results will vary based on your starting A1c, how consistently you take the medication, what you eat, and how active you are. Someone starting at an A1c of 10% will typically see a much larger drop than someone starting at 7.5%, even on the same drug. Medication is one part of the equation. It works best alongside the dietary changes, physical activity, and consistent monitoring that keep blood sugar stable between doses.