Type 2 Diabetes: History of Treatment Over Decades

The Pre-Insulin Era and Early Dietary Therapy (Before 1950)

Before any pharmacological agent existed, clinicians managed what we now call type 2 diabetes almost entirely through caloric restriction. Frederick Allen popularized the "starvation diet" at Rockefeller University around 1914, limiting patients to as few as 400 kilocalories per day. That approach kept blood glucose lower but caused severe malnutrition in many patients.

The discovery of insulin in 1921 by Banting, Best, Collip, and Macleod transformed type 1 diabetes care almost overnight. Its application to type 2 diabetes followed, though clinicians quickly recognized that many adult-onset patients retained residual beta-cell function and did not strictly require insulin to survive. By the 1940s, dietary carbohydrate restriction remained the primary intervention for non-insulin-dependent diabetes, supported mainly by clinical observation rather than controlled trials.

What the earliest treatment guidelines actually said

The American Diabetes Association, founded in 1940, published its first dietary recommendations that same decade. Those early statements emphasized weight reduction and carbohydrate limitation but offered no pharmacological pathway beyond insulin for patients who could not achieve adequate control through diet alone. The ADA's evolving standards are catalogued at diabetesjournals.org.

Insulin in type 2 diabetes: an early but imperfect tool

Insulin use in type 2 patients during the 1930s and 1940s was largely empirical. Dosing had no standardized titration protocol, hypoglycemia was common, and weight gain complicated metabolic goals. That gap created strong clinical demand for an oral agent.

Sulfonylureas: The First Oral Revolution (1950s to 1970s)

The first oral antidiabetic class emerged by accident. German researchers working on antibacterial sulfonamides in the early 1950s noticed that one compound, carbutamide, produced severe hypoglycemia in patients. By 1955 carbutamide was introduced in Europe as the first sulfonylurea. Tolbutamide, safer and better tolerated, reached the US market in 1957. [1]

Sulfonylureas stimulate pancreatic beta cells to secrete insulin independently of glucose concentration. That mechanism works well when beta-cell reserve is adequate, but it carries a linear hypoglycemia risk that later drug classes reduced significantly.

The UGDP controversy and its lasting impact

The University Group Diabetes Program (UGDP) published findings in 1970 suggesting tolbutamide may increase cardiovascular mortality compared with insulin or placebo. The study design was criticized widely, but the FDA added a black-box warning to sulfonylurea labels that persisted for decades and primed cardiologists to scrutinize every new antidiabetic agent for cardiovascular safety. [2]

Second-generation sulfonylureas

Glipizide (1984), glyburide (1984), and glimepiride (1995) offered improved receptor selectivity and longer duration of action. Glimepiride's once-daily dosing and lower hypoglycemia frequency compared with glyburide made it the preferred sulfonylurea in many guideline hierarchies by the late 1990s. Sulfonylureas remain on the ADA formulary today primarily because of low acquisition cost, though guidelines now rank them below agents with cardiovascular outcome data. [3]

Metformin: The Biguanide That Survived (1950s Discovery, 1994 US Approval)

Metformin was synthesized from galegine, a compound in Galega officinalis (French lilac), and first described by Jean Sterne in 1957. Its mechanism centers on AMP-activated protein kinase activation in the liver, which suppresses hepatic gluconeogenesis and improves peripheral insulin sensitivity without stimulating insulin secretion. That hepatic-first mechanism produces negligible hypoglycemia risk when used as monotherapy.

Phenformin, a related biguanide, was withdrawn from the US market in 1977 after it caused fatal lactic acidosis at a rate of approximately 40 to 64 cases per 100,000 patient-years. Metformin's lactic acidosis rate is approximately 3 to 5 cases per 100,000 patient-years, primarily in patients with severely reduced kidney function. [4]

The UKPDS and metformin's evidence base

The UK Prospective Diabetes Study (UKPDS, N=5,102) remains the defining trial for type 2 diabetes pharmacotherapy. Published in The Lancet in 1998, the overweight subgroup randomized to metformin showed a 32% reduction in any diabetes-related endpoint, a 42% reduction in diabetes-related death, and a 36% reduction in all-cause mortality compared with conventional (diet-only) therapy, over a median 10.7-year follow-up. [5] The Lancet summary stated: "Metformin may be the first-line pharmacological therapy of choice in the overweight or obese patient with type 2 diabetes."

FDA approval in the United States came in 1994 under the brand name Glucophage. Extended-release formulations approved in 2000 reduced the gastrointestinal side effects that caused discontinuation in roughly 10 to 20% of patients on immediate-release formulations.

Metformin today: still first line, but with caveats

ADA Standards of Medical Care in Diabetes 2024 retain metformin as the preferred initial agent for most patients without established cardiovascular disease or chronic kidney disease, citing its safety record, weight-neutral to modest weight-loss profile, and extremely low cost. [3] Contraindication thresholds have been relaxed since a 2016 FDA label update; the drug is now considered acceptable down to an estimated glomerular filtration rate of 30 mL/min/1.73m2, with dose reduction starting at 45. [6]

Thiazolidinediones: Promise, Toxicity, and Partial Rehabilitation (1990s to 2000s)

Thiazolidinediones (TZDs) activate peroxisome proliferator-activated receptor gamma (PPAR-gamma), increasing insulin sensitivity in adipose tissue, muscle, and liver. Troglitazone reached the US market in 1997 but was withdrawn in 2000 after 94 confirmed cases of fulminant hepatic failure, including 63 deaths. [7]

Rosiglitazone and pioglitazone, both approved in 1999, did not carry hepatotoxicity risk. Rosiglitazone's story became one of the most consequential drug-safety episodes in endocrinology: a 2007 meta-analysis by Nissen and Wolski in the New England Journal of Medicine (N=15,560 across 42 trials) reported a 43% relative increase in myocardial infarction risk (odds ratio 1.43, 95% CI 1.03 to 1.98, P<0.05). [8] The FDA imposed prescribing restrictions in 2010, which were partially lifted in 2013 after RECORD trial re-analysis showed no statistically significant increase in MI rates.

Pioglitazone's cardiovascular signal

Pioglitazone fared better. The PROactive trial (N=5,238, 34.5-month follow-up) showed a non-significant 10% reduction in the primary composite endpoint but a significant 16% reduction in the secondary composite of all-cause mortality, non-fatal MI, and stroke (P=0.027). [9] Pioglitazone remains in use today, particularly in patients with non-alcoholic steatohepatitis, where it has shown histological benefit in controlled trials.

Incretin-Based Therapies: DPP-4 Inhibitors and Early GLP-1 Agonists (2000s)

The incretin effect, the observation that oral glucose produces more insulin secretion than intravenous glucose at identical blood levels, had been described in the 1960s. Glucagon-like peptide-1 (GLP-1) was identified as the primary incretin hormone in the 1980s. Its native half-life of 1 to 2 minutes made it clinically useless until molecular modification extended that duration.

DPP-4 inhibitors: modest efficacy, clean safety

Dipeptidyl peptidase-4 (DPP-4) inhibitors block the enzyme that degrades GLP-1, roughly doubling active GLP-1 levels. Sitagliptin was the first approved, in 2006. Saxagliptin, linagliptin, and alogliptin followed by 2013.

HbA1c reduction with DPP-4 inhibitors averages 0.5 to 0.8 percentage points in head-to-head trials, lower than sulfonylureas or GLP-1 receptor agonists but with near-zero hypoglycemia risk and weight neutrality. The SAVOR-TIMI 53 trial (saxagliptin, N=16,492) and EXAMINE trial (alogliptin, N=5,380) confirmed cardiovascular non-inferiority but also an unexpected 27% increase in heart failure hospitalization with saxagliptin (P=0.007). [10] That signal prompted guideline cautions against DPP-4 inhibitors in patients with existing heart failure.

Exenatide: the first injectable GLP-1 agonist

Exenatide, derived from Gila monster saliva protein exendin-4, was approved by the FDA in April 2005 as the first GLP-1 receptor agonist. Twice-daily injections reduced HbA1c by 0.8 to 1.0 percentage points and produced 2 to 3 kg mean weight loss over 30 weeks in key trials. [11] Once-weekly exenatide (Bydureon) reached the market in 2012.

GLP-1 Receptor Agonists: Cardiovascular Outcomes and Weight Loss (2010s to Present)

The GLP-1 receptor agonist class matured dramatically after FDA mandated cardiovascular outcome trials (CVOTs) for all new antidiabetic agents following the rosiglitazone controversy. That regulatory requirement, issued in 2008, produced the most strong cardiovascular trial dataset in diabetes drug history.

LEADER and SUSTAIN-6: liraglutide and semaglutide

The LEADER trial (N=9,340, median 3.8-year follow-up) showed liraglutide 1.8 mg daily reduced the primary MACE endpoint (cardiovascular death, non-fatal MI, non-fatal stroke) by 13% compared with placebo in patients with established cardiovascular disease (HR 0.87, 95% CI 0.78 to 0.97, P=0.01 for superiority). [12]

SUSTAIN-6 (N=3,297, 2-year follow-up) demonstrated that once-weekly subcutaneous semaglutide 0.5 mg and 1.0 mg reduced MACE by 26% vs. Placebo (HR 0.74, 95% CI 0.58 to 0.95, P<0.001 for non-inferiority, P=0.02 for superiority). [13]

SELECT (N=17,604, published 2023) extended semaglutide's cardiovascular evidence to people with obesity but without diabetes, showing a 20% MACE reduction, further anchoring the drug's cardioprotective profile. [14]

Oral semaglutide: PIONEER-6

Oral semaglutide 14 mg (Rybelsus), approved by the FDA in September 2019, produced cardiovascular non-inferiority in PIONEER-6 (N=3,183) with a 21% MACE reduction that trended toward superiority (HR 0.79, 95% CI 0.57 to 1.11). [15] It became the first oral GLP-1 receptor agonist available in any market.

SGLT2 Inhibitors: Kidney and Heart Benefits Beyond Glucose (2013 to Present)

Sodium-glucose cotransporter-2 (SGLT2) inhibitors block glucose reabsorption in the proximal tubule, causing glucosuria and approximately 60 to 80 grams of glucose excretion per day. The mechanism is entirely insulin-independent, meaning efficacy does not depend on beta-cell reserve.

Canagliflozin received FDA approval in March 2013, followed by dapagliflozin in January 2014 and empagliflozin in August 2014.

EMPA-REG OUTCOME: the cardiovascular turning point

EMPA-REG OUTCOME (N=7,020, median 3.1 years) showed empagliflozin 10 mg or 25 mg reduced cardiovascular death by 38% vs. Placebo (HR 0.62, 95% CI 0.49 to 0.77, P<0.001), hospitalization for heart failure by 35%, and progression of kidney disease by 39%. [16] The New England Journal of Medicine published these results in September 2015. They are widely credited with shifting the guideline hierarchy for type 2 diabetes pharmacotherapy.

CREDENCE and DAPA-CKD: kidney protection

CREDENCE (canagliflozin, N=4,401) was stopped early at a median 2.62 years because canagliflozin reduced the primary renal composite endpoint by 30% in patients with type 2 diabetes and diabetic kidney disease (HR 0.70, 95% CI 0.59 to 0.82, P=0.00001). [17] DAPA-CKD (dapagliflozin, N=4,304) extended kidney protection to patients without diabetes entirely, broadening the regulatory indication. The ADA now recommends SGLT2 inhibitors as first-line therapy alongside metformin for patients with chronic kidney disease or established heart failure, regardless of baseline HbA1c. [3]

Dual and Triple Incretin Agonism: The Tirzepatide Era (2022 to Present)

Tirzepatide (Mounjaro, approved by FDA in May 2022 for type 2 diabetes) activates both GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) receptors. The dual mechanism produces additive effects on glucose-dependent insulin secretion, glucagon suppression, and gastric emptying delay.

SURPASS trial program

In SURPASS-2 (N=1,879, 40 weeks), tirzepatide 5 mg, 10 mg, and 15 mg reduced HbA1c by 2.01, 2.24, and 2.30 percentage points respectively, compared with 1.86 percentage points for semaglutide 1.0 mg. All three tirzepatide doses were non-inferior to semaglutide; the 10 mg and 15 mg doses were superior (P<0.001). [18]

SURMOUNT-1 (N=2,539, 72 weeks, obesity population without diabetes) showed tirzepatide 15 mg produced a mean weight loss of 22.5% from baseline, the largest reported in any phase 3 pharmacotherapy trial at the time of publication. [19]

What the framework looks like now

The current clinical decision pathway for type 2 diabetes, as recommended by the ADA Standards of Medical Care 2024 and the American Association of Clinical Endocrinology 2023 algorithm, stratifies add-on therapy by comorbidity rather than by HbA1c alone. Patients with established atherosclerotic cardiovascular disease or high CV risk receive a GLP-1 receptor agonist with proven MACE benefit. Those with heart failure or CKD receive an SGLT2 inhibitor. Patients whose primary need is weight reduction receive tirzepatide or semaglutide 2.4 mg (Wegovy). Patients without these comorbidities may still appropriately receive a sulfonylurea or DPP-4 inhibitor on cost or tolerability grounds. [3]

Insulin Therapy in Type 2 Diabetes: Then and Now

Insulin use in type 2 diabetes has shifted from a late-stage rescue therapy to a precision tool used at specific stages. The introduction of NPH insulin in 1950, followed by Lente and Ultralente formulations, gave clinicians tools for more physiologic replacement.

Basal insulin analogs

Insulin glargine (Lantus, approved 2000) and insulin detemir (Levemir, approved 2005) provided 24-hour basal coverage with flatter pharmacokinetic profiles than NPH, reducing nocturnal hypoglycemia. The ORIGIN trial (N=12,537, median 6.2 years) showed glargine-based therapy in pre-diabetes and early type 2 diabetes produced cardiovascular non-inferiority without increasing cancer risk, settling a then-active safety debate. [20]

Insulin degludec (Tresiba, approved 2015) extended duration to over 42 hours and reduced nocturnal hypoglycemia by 54% compared with glargine in the SWITCH 2 trial (N=721). [21]

Combination injectables

The combination of basal insulin with a GLP-1 receptor agonist in a single injection pen, iGlarLixi (insulin glargine plus lixisenatide) and IDegLira (degludec plus liraglutide), approved in 2016 and 2017 respectively, reduced the injection burden and mitigated the weight gain typically associated with insulin intensification.

Bariatric Surgery and Metabolic Remission

Bariatric surgery entered the type 2 diabetes treatment narrative formally through the STAMPEDE trial (N=150, 5-year follow-up, published 2017 in NEJM), which showed that gastric bypass and sleeve gastrectomy achieved HbA1c <6.0% without antidiabetic medications in 29% and 23% of patients respectively, compared with 5% in the intensive medical therapy group. [22] These results changed ADA guidelines to include metabolic surgery as a treatment option for type 2 diabetes in patients with BMI >30 kg/m2 who do not achieve adequate control through lifestyle and pharmacotherapy.

Timeline Summary: Drug Classes by Decade

| Decade | Major Addition | Key Mechanism | |--------|---------------|---------------| | 1950s | Sulfonylureas (tolbutamide) | Beta-cell insulin secretion | | 1950s | Metformin (European use) | Hepatic gluconeogenesis suppression | | 1990s | TZDs (troglitazone, pioglitazone) | PPAR-gamma agonism | | 1990s | Metformin US approval; repaglinide | Multiple | | 2000s | DPP-4 inhibitors (sitagliptin) | GLP-1 preservation | | 2005 | GLP-1 RA (exenatide) | Incretin receptor activation | | 2013 | SGLT2 inhibitors (canagliflozin) | Glucosuria | | 2022 | Dual GIP/GLP-1 (tirzepatide) | Dual incretin receptor agonism |