Several classes of medications lower blood sugar, and they work through surprisingly different mechanisms. The right one depends on whether you have type 1 or type 2 diabetes, how much blood sugar lowering you need, and whether benefits like weight loss or heart protection matter to your situation. Here’s how each major category works and what sets them apart.
Metformin: The Usual Starting Point
Metformin is the most widely prescribed diabetes medication in the world and typically the first one doctors reach for in type 2 diabetes. It works on three fronts: it reduces the amount of sugar your liver releases into your bloodstream, decreases the sugar you absorb from food, and helps your cells use insulin more effectively.
In clinical trials, metformin lowered A1c (a measure of average blood sugar over roughly three months) by about 0.7 to 1.0 percentage points on its own. When combined with insulin, patients saw A1c reductions of around 2.1 percentage points, compared to 1.6 points with insulin alone. It’s taken as a pill, usually once or twice daily, and is generally well tolerated. The most common side effects are digestive: nausea, diarrhea, and stomach upset, which often ease over time. Metformin doesn’t cause weight gain, which gives it an edge over some older medications.
GLP-1 Receptor Agonists
GLP-1 receptor agonists have become one of the most talked-about drug classes in diabetes care, partly because of their significant effect on weight. Names you may recognize include semaglutide (Ozempic), dulaglutide (Trulicity), liraglutide (Victoza), and exenatide (Byetta and Bydureon). These medications mimic a gut hormone called GLP-1 that your body naturally releases after eating. They boost insulin production when blood sugar is high, slow stomach emptying so you feel full longer, and reduce appetite signals in the brain.
The weight loss effect is substantial. In some studies, people using GLP-1 medications lost an average of 10% to 15% of their body weight over a year, with the most effective versions producing losses above 20%. Most GLP-1 medications are injected, with dosing schedules ranging from twice daily to once weekly depending on the specific drug. An oral version of semaglutide also exists. The most common side effects are gastrointestinal: nausea, vomiting, and diarrhea, which tend to be worst in the first few weeks and improve as your body adjusts.
Dual GLP-1/GIP Agonists
Tirzepatide (Mounjaro) represents a newer approach that activates two hormone receptors instead of one. It targets both GLP-1 and GIP receptors on cells in the brain, pancreas, and elsewhere. The combined effect promotes feelings of fullness, reduces appetite, and boosts insulin secretion. In trials, tirzepatide led to greater weight loss and fewer side effects than older GLP-1-only compounds. A three-year trial also showed a powerful diabetes-prevention effect in people at high risk. Tirzepatide is injected once weekly.
SGLT2 Inhibitors
SGLT2 inhibitors take a completely different approach: they make your kidneys flush excess sugar out through urine. Common options include empagliflozin (Jardiance), dapagliflozin (Farxiga), and canagliflozin (Invokana). All are taken as daily pills.
What makes this class stand out is its benefits beyond blood sugar. SGLT2 inhibitors slow the progression of kidney disease, reduce the risk of needing dialysis, and lower the risk of heart failure flare-ups. These benefits are significant enough that some people without diabetes now take them for heart or kidney protection alone. In 2024, the FDA expanded approval of dapagliflozin (Farxiga) to include children aged 10 and older with type 2 diabetes, reflecting growing confidence in the drug’s safety profile. Side effects can include urinary tract infections and yeast infections, since sugar in the urine creates a more hospitable environment for those organisms.
DPP-4 Inhibitors
DPP-4 inhibitors, such as sitagliptin (Januvia), work on the same hormonal pathway as GLP-1 agonists but in a milder way. Instead of mimicking GLP-1 directly, they block the enzyme that breaks it down, letting your body’s own GLP-1 stick around longer. The result is a modest blood sugar reduction with very few side effects.
The tradeoff is potency. Head-to-head studies consistently show that DPP-4 inhibitors lower A1c less than GLP-1 agonists. They also don’t produce meaningful weight loss, making them “weight neutral.” However, they’re taken as pills, rarely cause nausea, and have a low risk of causing dangerously low blood sugar. For people who can’t tolerate GLP-1 agonists or prefer a simpler oral medication, they fill a useful niche.
Sulfonylureas and Meglitinides
Sulfonylureas (glipizide, glimepiride, glyburide) and meglitinides are older oral medications that stimulate your pancreas to release more insulin regardless of what your blood sugar is doing at that moment. They’re effective and inexpensive, which keeps them in use worldwide.
The major downside is hypoglycemia, meaning blood sugar that drops too low. Because these drugs push insulin out on a fixed schedule rather than responding to what your body needs in real time, they carry a higher risk of low blood sugar episodes compared to newer classes like DPP-4 inhibitors, GLP-1 agonists, or SGLT2 inhibitors. They also tend to cause weight gain. For these reasons, they’ve gradually moved down the prescribing ladder as newer options have become available, though they remain a reasonable choice when cost is a primary concern.
Insulin
Insulin is the oldest and most direct way to lower blood sugar. Everyone with type 1 diabetes needs it, and many people with type 2 diabetes eventually use it as their condition progresses. Modern insulin comes in several speeds, and understanding the timing helps make sense of how it’s used.
Rapid-acting insulins (like lispro, aspart, and glulisine) start working within 5 to 15 minutes, peak at 1 to 3 hours, and wear off in 3 to 5 hours. You take them right before or with meals to cover the blood sugar spike from eating. Ultra-long-acting insulins work on a completely different timeline. Insulin glargine U-300 (Toujeo) takes about 6 hours to kick in but lasts up to 36 hours with no sharp peak. Insulin degludec (Tresiba) starts within an hour and lasts up to 42 hours, also without a peak. These long-acting versions provide steady background coverage, keeping blood sugar stable between meals and overnight.
Many people on insulin use both types: a long-acting injection once daily for baseline coverage and rapid-acting doses at meals. The main risk is hypoglycemia, particularly with rapid-acting formulations where a miscalculated dose or skipped meal can drop blood sugar quickly. Weight gain is also common with insulin therapy.
How These Medications Compare
The differences between classes boil down to a few practical questions:
- Blood sugar lowering power: Insulin and GLP-1 agonists produce the largest A1c reductions. Metformin and SGLT2 inhibitors fall in the middle. DPP-4 inhibitors are the mildest.
- Weight effects: GLP-1 agonists and dual agonists like tirzepatide cause the most weight loss. SGLT2 inhibitors produce modest weight loss. Metformin and DPP-4 inhibitors are roughly weight neutral. Sulfonylureas and insulin tend to cause weight gain.
- Low blood sugar risk: Sulfonylureas, meglitinides, and insulin carry the highest risk. Metformin, SGLT2 inhibitors, DPP-4 inhibitors, and GLP-1 agonists rarely cause hypoglycemia on their own.
- Heart and kidney protection: SGLT2 inhibitors and GLP-1 agonists have the strongest evidence for reducing cardiovascular and kidney disease risk beyond just lowering blood sugar.
- How you take them: Metformin, SGLT2 inhibitors, DPP-4 inhibitors, and sulfonylureas are all pills. Most GLP-1 agonists and all insulins are injected, though an oral semaglutide exists. Injection frequency ranges from daily to weekly for non-insulin options.
Most people with type 2 diabetes start on metformin and add other medications over time as needed. The choice of what to add depends on your priorities: whether weight loss, heart protection, kidney health, cost, or simplicity matters most. Many people end up on two or three medications from different classes working together.