Blood sugar medications fall into several distinct classes — metformin, GLP-1 receptor agonists, SGLT2 inhibitors, insulin, sulfonylureas, DPP-4 inhibitors, thiazolidinediones (TZDs), meglitinides, and alpha-glucosidase inhibitors. Each has a different mechanism, different side-effect profile, and different role in a treatment plan. Metformin is the usual starting point for type 2 diabetes; GLP-1 and SGLT2 drugs now play prominent second-line roles because they add cardiovascular and kidney benefits on top of glucose control.
The Main Classes at a Glance
| Class | Examples | Route | Typical A1C Reduction | Weight Effect | Hypoglycemia Risk |
|---|---|---|---|---|---|
| Biguanide | Metformin | Oral | -1.0 to -1.5% | Neutral to mild loss | Very low |
| GLP-1 agonist | Semaglutide, dulaglutide, liraglutide, exenatide | Injection (oral for Rybelsus) | -1.0 to -2.0% | Loss (2 to 15%+) | Low |
| Dual GLP-1/GIP agonist | Tirzepatide | Injection | -1.5 to -2.5% | Loss (10 to 22%) | Low |
| SGLT2 inhibitor | Empagliflozin, dapagliflozin, canagliflozin, ertugliflozin | Oral | -0.5 to -1.0% | Loss (2 to 3 kg) | Low |
| DPP-4 inhibitor | Sitagliptin, linagliptin, saxagliptin, alogliptin | Oral | -0.5 to -0.8% | Neutral | Low |
| Sulfonylurea | Glipizide, glimepiride, glyburide | Oral | -1.0 to -2.0% | Gain (1 to 3 kg) | Moderate to high |
| Meglitinide | Repaglinide, nateglinide | Oral | -0.5 to -1.5% | Modest gain | Moderate |
| Thiazolidinedione (TZD) | Pioglitazone, rosiglitazone | Oral | -1.0 to -1.5% | Gain (2 to 4 kg) | Low |
| Alpha-glucosidase inhibitor | Acarbose, miglitol | Oral | -0.5 to -0.8% | Neutral | Low |
| Insulin | Glargine, detemir, degludec, lispro, aspart, regular, NPH | Injection | Unlimited | Gain (1 to 5+ kg) | High |
Metformin: The Foundation
Metformin is first-line for type 2 diabetes because it works, costs pennies, does not cause hypoglycemia, and has decades of safety data. It works mainly by reducing glucose production in the liver and modestly improving insulin sensitivity in muscle. It is also the only medication the ADA recommends for prediabetes in high-risk patients — those under age 60 with BMI ≥35 or history of gestational diabetes. Common side effects are GI (nausea, diarrhea, metallic taste) and long-term B12 deficiency; rare but serious is lactic acidosis in kidney failure.
GLP-1 Receptor Agonists
GLP-1 agonists mimic the gut hormone glucagon-like peptide-1. They lower glucose through multiple mechanisms — increased insulin release, reduced glucagon, slower gastric emptying, and reduced appetite — and have become pillars of modern type 2 diabetes care. The class includes semaglutide (Ozempic, Wegovy, Rybelsus), dulaglutide (Trulicity), liraglutide (Victoza, Saxenda), and exenatide (Byetta, Bydureon). Tirzepatide (Mounjaro, Zepbound) is a dual GLP-1/GIP agonist with even stronger effects. Common side effects are GI — nausea, vomiting, diarrhea, constipation — usually resolving over 4 to 8 weeks.
SGLT2 Inhibitors
These drugs block the sodium-glucose co-transporter 2 in the kidney, causing excess glucose to be excreted in urine. Examples include empagliflozin (Jardiance), dapagliflozin (Farxiga), canagliflozin (Invokana), and ertugliflozin (Steglatro). Beyond glucose lowering, SGLT2s have major benefits in heart failure (reduced or preserved ejection fraction), chronic kidney disease, and atherosclerotic cardiovascular disease. Common side effects are genital yeast infections and urinary tract infections; rare but serious are euglycemic DKA and volume depletion.
DPP-4 Inhibitors
DPP-4 inhibitors prevent breakdown of endogenous GLP-1, producing modest glucose-lowering. Examples include sitagliptin (Januvia), linagliptin (Tradjenta), saxagliptin (Onglyza), and alogliptin (Nesina). They are weight-neutral, cause little hypoglycemia, and are widely tolerated but produce less dramatic A1C reduction than GLP-1 injections and no cardiovascular or kidney benefit.
Sulfonylureas
Sulfonylureas — glipizide, glimepiride, glyburide — stimulate insulin release from the pancreas. They are effective and cheap but carry meaningful hypoglycemia risk, cause weight gain, and lose effectiveness as beta cells fail over years. Once a mainstay, they are now typically second- or third-line after metformin, GLP-1 agonists, and SGLT2 inhibitors.
Thiazolidinediones (TZDs)
Pioglitazone (Actos) is the most commonly used TZD. It directly improves insulin sensitivity in muscle and fat tissue through PPAR-gamma receptor activation. It causes weight gain, fluid retention, increased heart failure risk, and slightly increased bone fracture risk. Rosiglitazone (Avandia) was heavily restricted after cardiovascular concerns. TZDs are occasionally useful for patients with significant insulin resistance where other options are not tolerated.
Meglitinides and Alpha-Glucosidase Inhibitors
- Meglitinides (repaglinide, nateglinide) are short-acting insulin secretagogues taken before each meal. Useful for patients with irregular meal timing but carry hypoglycemia risk.
- Alpha-glucosidase inhibitors (acarbose, miglitol) slow carbohydrate digestion in the gut. Modest A1C reduction; GI side effects are common and limit use.
Insulin
Insulin is the most powerful glucose-lowering medication and is essential in type 1 diabetes and many advanced type 2 cases. It is also the medication with the highest hypoglycemia risk and requires careful dose adjustment. Modern insulins are grouped by onset and duration — rapid, short, intermediate, long, and ultra-long acting. See our detailed guide on the different types of insulin.
How Combinations Work
As type 2 diabetes progresses, combination therapy becomes common. Typical stepwise approach:
- Metformin
- Add a GLP-1 receptor agonist or SGLT2 inhibitor (especially if cardiovascular or kidney disease is present)
- Add a DPP-4 inhibitor, sulfonylurea, or TZD if more A1C reduction is needed
- Add basal insulin
- Add mealtime insulin (basal-bolus therapy)
Combination pills such as Janumet (metformin + sitagliptin), Synjardy (metformin + empagliflozin), and Xigduo XR (metformin + dapagliflozin) simplify regimens.
Non-Diabetes Indications
Several blood sugar medications are also used outside of diabetes:
- Metformin for PCOS and weight management
- GLP-1 agonists (semaglutide, tirzepatide) for obesity and cardiovascular risk reduction
- SGLT2 inhibitors for heart failure and chronic kidney disease, with or without diabetes
- Pioglitazone for nonalcoholic fatty liver disease (NASH) in specific cases
When Medications Are Not Enough
For severe insulin-resistant obesity, bariatric surgery remains the most durable intervention and often allows medication reductions. For specific patients with type 1 diabetes, islet cell or pancreas transplantation is an option. Research into immune modulation therapies (e.g., teplizumab to delay type 1 diabetes onset) is ongoing.
Related Reading
See our treatment hub, A1C levels guide, and reversing prediabetes overview for how these medications fit into comprehensive care.
The Bottom Line
Blood sugar medications are not a single category — they are a toolkit with different mechanisms, benefits, and trade-offs. Metformin is the foundation for type 2 diabetes; GLP-1 agonists and SGLT2 inhibitors are the modern second-line options with added cardiovascular and kidney protection; insulin remains essential for type 1 and advanced type 2 disease. Other classes fill specific roles. Work with your clinician to match the medication mix to your A1C, weight, kidney function, heart status, cost constraints, and lifestyle — the “right” regimen is the one that fits your whole picture, not the newest drug.
