Diabetes Medications —
Compared

Metformin has been the most widely prescribed diabetes medication in the world for decades, and for good reason. It reduces the liver's excess glucose production (the main driver of fasting hyperglycemia in type 2 diabetes), improves the ability of muscle cells to take up glucose, and does not stimulate insulin secretion — meaning it cannot cause hypoglycemia on its own.

It is inexpensive (widely available as a generic), does not cause weight gain, and has a safety record spanning many decades. Current guidelines recommend it as first-line therapy for most people with type 2 diabetes, used as a foundation on which other agents are added as needed.

The main side effects are gastrointestinal — nausea, diarrhea, and stomach upset — which are most pronounced when starting and usually improve with time or by using the extended-release formulation taken with food. A rare but serious risk is lactic acidosis, which is why metformin is generally withheld before procedures using iodinated contrast dye and in patients with severely reduced kidney function.

Semaglutide has transformed both diabetes and obesity treatment. As a GLP-1 receptor agonist, it mimics the gut hormone GLP-1 with a half-life engineered for once-weekly injection (or once-daily oral use). The injectable form (Ozempic for diabetes, Wegovy at higher strengths for weight management) and the oral tablet form (Rybelsus) are the same molecule at different formulations.

Its mechanisms overlap and reinforce each other: glucose-dependent insulin stimulation means it cannot cause hypoglycemia on its own; glucagon suppression reduces hepatic glucose production; slowed gastric emptying reduces post-meal glucose spikes; and central appetite suppression leads to significant calorie reduction and weight loss in most people.

Side effects are predominantly GI — nausea, vomiting, diarrhea, constipation — particularly during initial use and dose escalation. These typically improve with continued therapy. Rare but serious risks include pancreatitis; the drug carries a warning regarding medullary thyroid cancer (based on animal data) and is contraindicated in those with a personal or family history of this cancer or Multiple Endocrine Neoplasia type 2.

Tirzepatide is the first approved drug to simultaneously activate two incretin receptors: GLP-1 and GIP. While GLP-1 agonism is well established, the addition of GIP receptor activation appears to amplify the overall effect on both blood glucose and body weight. In the SURPASS clinical trial program, tirzepatide outperformed semaglutide for both HbA1c reduction and weight loss at comparable doses.

The SURMOUNT obesity trials showed average weight reductions of roughly 20% of body weight with the highest strength — results not previously seen with any approved medication. Zepbound is the brand name for the weight management indication.

Side effects mirror the GLP-1 class: GI symptoms dominate (nausea, diarrhea, vomiting, constipation), typically most prominent during dose escalation. The same thyroid tumor warning applies. Administered as a once-weekly subcutaneous injection via a prefilled pen.

Empagliflozin exemplifies how SGLT2 inhibitors have evolved beyond glucose control. The EMPA-REG OUTCOME trial was landmark: it showed empagliflozin reduced cardiovascular death and heart failure hospitalization in people with established cardiovascular disease, making it one of the first diabetes medications shown to extend life beyond glucose lowering.

Its mechanism — blocking glucose reabsorption in the kidney — also causes osmotic diuresis (more urine production), which reduces fluid overload, lowers blood pressure slightly, and reduces the strain on the failing heart. This cardioprotective effect led to empagliflozin's approval for heart failure in patients both with and without diabetes, and for chronic kidney disease.

Unique side effect considerations for the class include genital mycotic infections (yeast infections), increased urinary tract infections, and a rare but serious condition called euglycemic diabetic ketoacidosis (where the blood is acidic even though glucose is not markedly elevated). Patients should be educated to stop the medication and seek care during illness, surgery, or prolonged fasting.

Sitagliptin was the first DPP-4 inhibitor approved in the United States (2006) and remains the most widely prescribed member of its class. It works by blocking the enzyme that destroys the body's own GLP-1 and GIP hormones, effectively amplifying the natural incretin effect that occurs after eating without directly stimulating insulin secretion at rest.

Because its mechanism is glucose-dependent, sitagliptin has an excellent safety profile: very low risk of hypoglycemia when used alone, and no meaningful effect on weight. It is generally well tolerated, with nasopharyngitis (common cold-like symptoms) and headache as the most frequently reported side effects in trials.

Dose adjustment is required in patients with reduced kidney function because sitagliptin is renally excreted — in contrast to linagliptin, which does not require dose adjustment. The TECOS cardiovascular outcomes trial found sitagliptin to be cardiovascularly neutral — neither harmful nor protective — unlike the SGLT2 inhibitors and GLP-1 agonists which showed active benefit.

Sulfonylureas (glipizide, glimepiride, glyburide) have been used to treat type 2 diabetes for over 60 years. They work by binding to a receptor on pancreatic beta cells that triggers insulin release — independent of blood glucose level. This unconditional insulin release is effective at lowering blood sugar but carries inherent risks: hypoglycemia (because insulin is released even if glucose is already normal or low) and weight gain (because insulin is an anabolic hormone that promotes fat storage).

Within the class, glyburide carries the highest hypoglycemia risk — it has a longer duration and more potent effect, and it is generally avoided in elderly patients. Glimepiride and glipizide are considered safer alternatives within the class. All sulfonylureas become less effective over time as pancreatic beta cell function declines.

Despite their side effect profile, sulfonylureas remain widely prescribed because they are highly effective at lowering blood glucose, inexpensive, and available in simple once-daily oral formulations. They are often added when first-line agents are insufficient and cost is a significant concern.

Insulin is the essential treatment for type 1 diabetes and an important option in advanced type 2 diabetes. Modern insulin therapy separates basal (background) insulin from bolus (mealtime) insulin to mimic what a healthy pancreas does naturally throughout the day.

Rapid-acting insulins (lispro/Humalog, aspart/NovoLog, glulisine/Apidra) are designed to act quickly — covering the blood glucose rise from meals. They begin acting within minutes of injection. They carry the highest hypoglycemia risk because timing relative to eating matters significantly.

Long-acting (basal) insulins (glargine/Lantus, detemir/Levemir, degludec/Tresiba) provide a slow, steady release over many hours to cover background glucose production by the liver overnight and between meals. They have a lower but real hypoglycemia risk — particularly overnight. Degludec (Tresiba) has the longest duration (over 42 hours) and the flattest profile, offering flexibility in injection timing.

All insulins cause weight gain over time (insulin promotes glucose uptake into cells and fat storage) and require injection. Modern insulin pen devices have made injection much more convenient than traditional vials and syringes.