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Noninsulin Diabetes Drugs: Selection & Adverse Effects

Name: Noninsulin Diabetes Drugs: Selection & Adverse Effects
Creator: Veli Bakalov, MD

Let the comorbidity pick the drug—and know each class's signature harm

Endocrinology·Diabetes & Metabolism·6 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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Metformin is first-line: it suppresses hepatic gluconeogenesis without hypoglycemia or weight gain and causes GI upset and B12 deficiency.
Metformin is contraindicated at eGFR <30, not started at 30–45, and held at the time of iodinated contrast when eGFR is 30–60.
With ASCVD add a GLP-1 RA with proven MACE benefit (liraglutide, semaglutide, dulaglutide) or an SGLT2 inhibitor, regardless of A1c.
Heart failure with reduced or preserved EF, or albuminuric CKD with eGFR ≥20, calls for an SGLT2 inhibitor continued until dialysis.
Obesity favors semaglutide or tirzepatide; when cost limits choice, use a sulfonylurea (glipizide) or pioglitazone.
Sulfonylureas cause hypoglycemia and weight gain (avoid glyburide in older adults and CKD); pioglitazone causes edema and heart failure, fractures and a bladder cancer signal.
GLP-1 RAs cause nausea, pancreatitis and gallstones and are contraindicated with a personal or family history of medullary thyroid carcinoma or MEN2.
SGLT2 inhibitors cause genital mycotic infections, volume depletion, euglycemic DKA and Fournier gangrene; hold them 3–4 days before surgery and during acute illness.
DPP-4 inhibitors are weight-neutral and weak (saxagliptin raises heart failure admissions); frail older adults get an A1c goal of about 8% and no hypoglycemia-prone drugs.

Principles of drug selection

Targets. An HbA1c below 7% suits most nonpregnant adults, and a tighter goal is reasonable if it can be reached without hypoglycemia. Frail older adults and those with limited life expectancy, cognitive impairment or recurrent hypoglycemia get a relaxed goal of about 8%. Lifestyle change underlies every regimen.

Metformin plus comorbidity-driven add-ons. Metformin remains the usual first drug unless contraindicated. The next agent is chosen by comorbidity rather than HbA1c alone: in established or high-risk atherosclerotic cardiovascular disease (ASCVD), heart failure or CKD, a GLP-1 receptor agonist (GLP-1 RA) or SGLT2 inhibitor with proven outcome benefit is added regardless of HbA1c or background metformin. When HbA1c is 1.5–2% above goal, starting two drugs together is reasonable, and HbA1c above 10% or catabolic symptoms call for insulin.

Choosing therapy by patient priority

Priority	Preferred	Avoid or use caution
ASCVD (prior MI, stroke, PAD)	GLP-1 RA with MACE benefit (liraglutide, semaglutide, dulaglutide) or SGLT2i (empagliflozin, canagliflozin)	Relying on CV-neutral agents alone
Heart failure (reduced or preserved EF)	SGLT2i (dapagliflozin, empagliflozin)	Pioglitazone; saxagliptin, alogliptin
CKD with albuminuria or eGFR 20–60	SGLT2i if eGFR ≥20; GLP-1 RA if not tolerated	Metformin below eGFR 30; glyburide
Obesity	Semaglutide or tirzepatide	Insulin, sulfonylureas, pioglitazone
MASLD with fibrosis	Pioglitazone or GLP-1 RA	—
Cost limits	Sulfonylurea (glipizide), pioglitazone, human NPH and regular insulin	—
Frail older adult	Metformin (eGFR permitting), DPP-4i, other low-hypoglycemia agents	Glyburide, complex insulin regimens

Metformin

Action and benefits. Metformin, a biguanide, activates AMP-activated protein kinase, suppressing hepatic gluconeogenesis and improving insulin sensitivity. It lowers HbA1c about 1–1.5%, is weight-neutral, does not cause hypoglycemia on its own and is inexpensive; it is also used in prediabetes and polycystic ovary syndrome.

GI effects and B12. Diarrhea, nausea and a metallic taste are common early; slow titration, dosing with meals and extended-release tablets help. Long-term use reduces ileal B12 absorption, causing megaloblastic anemia or a neuropathy easily mistaken for diabetic neuropathy, so B12 is checked periodically.

Lactic acidosis. Rare but potentially fatal, it occurs when metformin accumulates or lactate production rises: renal failure, hypoxemia, shock, sepsis, decompensated heart failure, liver failure and heavy alcohol use.

eGFR ≥45Full dosing.
eGFR 30–45Do not start; if already taking it, reassess and reduce the dose.
eGFR <30Contraindicated; stop.
Iodinated contrastHold at the time of the study if eGFR is 30–60, or with liver disease, alcohol misuse, heart failure or intra-arterial contrast; restart when eGFR is stable 48 h later.

Sulfonylureas and pioglitazone

Sulfonylureas. Glipizide, glimepiride and glyburide close ATP-sensitive potassium channels on β cells, releasing insulin regardless of glucose. They lower HbA1c about 1–1.5% and are cheap, but cause hypoglycemia (especially in older adults, CKD and with missed meals) and weight gain, and their effect wanes as β-cell function declines. Glyburide, long-acting with renally cleared active metabolites, is avoided in older adults and CKD; glipizide, cleared by the liver, is preferred. Sulfonylurea hypoglycemia can be prolonged and often requires admission. Meglitinides (repaglinide, nateglinide) act on the same channel but briefly and are taken with meals.

Pioglitazone. This thiazolidinedione activates PPAR-γ, increasing insulin sensitivity in fat, muscle and liver. It lowers HbA1c about 1% without hypoglycemia, needs several weeks for full effect and improves MASH. Its costs are weight gain, fluid retention with edema and heart failure (boxed warning; contraindicated in NYHA class III–IV), distal fractures (particularly in women), macular edema and a bladder cancer signal, so it is avoided with active or prior bladder cancer or unexplained hematuria.

Incretin-based therapies

GLP-1 receptor agonists. Semaglutide, liraglutide, dulaglutide and exenatide stimulate glucose-dependent insulin secretion, suppress glucagon, slow gastric emptying and increase satiety. HbA1c falls about 1–2% with substantial weight loss and little hypoglycemia unless combined with insulin or a sulfonylurea. Liraglutide, subcutaneous semaglutide and dulaglutide reduced major adverse cardiovascular events. Most are daily or weekly injections; semaglutide also comes as a tablet. Tirzepatide, a dual GIP and GLP-1 receptor agonist, produces the greatest weight loss, and it or semaglutide is chosen when weight is a priority.

GLP-1 RA adverse effects. Nausea, vomiting and diarrhea are dose-related and eased by slow titration. Pancreatitis mandates discontinuation, and the class is avoided after prior pancreatitis. Rapid weight loss promotes gallstones and cholecystitis. Because C-cell tumors arose in rodents, a personal or family history of medullary thyroid carcinoma or MEN2 is a contraindication. Rapid HbA1c reduction can transiently worsen retinopathy, and slowed gastric emptying raises aspiration risk during anesthesia and endoscopy. Tirzepatide reduces oral contraceptive absorption, so a non-oral or backup method is advised for 4 weeks after starting and after each dose increase.

DPP-4 inhibitors. Sitagliptin, saxagliptin, linagliptin and alogliptin block the enzyme that degrades endogenous GLP-1 and GIP. They are oral, weight-neutral, well tolerated in older adults and do not cause hypoglycemia alone, but lower HbA1c only about 0.5–0.8% and are cardiovascularly neutral. All except linagliptin, which is eliminated mainly in bile, need renal dose reduction. Saxagliptin (and possibly alogliptin) increased heart failure hospitalization; pancreatitis, arthralgia and bullous pemphigoid are rare. Combining a DPP-4 inhibitor with a GLP-1 RA adds nothing.

SGLT2 inhibitors

Mechanism. Empagliflozin, dapagliflozin, canagliflozin and ertugliflozin block sodium-glucose cotransport in the proximal tubule, causing glycosuria and natriuresis. HbA1c falls about 0.5–1% with 2–3 kg of weight loss and lower blood pressure, and there is no hypoglycemia alone. Extra sodium reaching the macula densa restores tubuloglomerular feedback, constricting the afferent arteriole and lowering intraglomerular pressure; an early eGFR dip is expected and benign.

Cardiorenal benefit. These drugs reduce heart failure hospitalization and cardiovascular death in heart failure with reduced or preserved ejection fraction, with or without diabetes, and slow CKD progression. They can be started at eGFR ≥20 and continued until dialysis; glucose lowering fades below an eGFR of about 45, but organ protection persists.

Adverse effects. Genital mycotic infections are the most common, and UTIs are slightly more frequent. Osmotic diuresis can cause volume depletion, hypotension and prerenal AKI, especially in older adults on loop diuretics. Euglycemic DKA, an anion-gap ketoacidosis with glucose often below 250 mg/dL, is provoked by surgery, fasting, acute illness, alcohol or very low-carbohydrate diets, so the drugs are held during acute illness and 3–4 days before surgery; treatment is insulin plus dextrose. Fournier gangrene, a perineal necrotizing fasciitis, is rare but needs emergency debridement and IV antibiotics. Canagliflozin carried an amputation signal.

Older adults and class comparison

Older adults. Hypoglycemia causes falls, arrhythmias and cognitive decline, so frail patients get a relaxed HbA1c goal of about 8% and simpler regimens. Sulfonylureas and insulin are deintensified when HbA1c is below goal or lows occur, while metformin (if eGFR allows), DPP-4 inhibitors, GLP-1 RAs and SGLT2 inhibitors carry little hypoglycemia risk.

Noninsulin classes at a glance

Class	HbA1c fall	Weight	Hypoglycemia alone	Signature adverse effects
Metformin	1–1.5%	Neutral	No	GI upset, B12 deficiency, lactic acidosis
Sulfonylureas	1–1.5%	Gain	Yes	Prolonged hypoglycemia (glyburide)
Pioglitazone	~1%	Gain	No	Edema, heart failure, fractures, bladder cancer signal
GLP-1 RAs	1–2%	Loss	No	Nausea, pancreatitis, gallstones; MTC/MEN2 contraindication
SGLT2 inhibitors	0.5–1%	Loss	No	Genital infections, volume depletion, euglycemic DKA, Fournier gangrene
DPP-4 inhibitors	0.5–0.8%	Neutral	No	Saxagliptin HF signal, bullous pemphigoid

Meglitinides, like sulfonylureas and insulin, can cause hypoglycemia on their own.

Hypoglycemia in a patient taking acarbose, an α-glucosidase inhibitor, must be treated with glucose rather than sucrose, because disaccharide digestion is blocked.