Clinical Evidence: HbA1c Effect Sizes for Diabetes Medications and Supplements

This page collects verified PubMed / PubMed Central citations behind the reported HbA₁c effect size for every medication and supplement in the calculator. Reported ranges come from meta-analyses and RCTs and vary by population, dose, baseline HbA₁c, and study duration; individual results vary. A few older sulfonylureas predate HbA₁c as a standard trial endpoint, so their evidence is noted as weaker by nature of the available literature. This is general clinical literature, not a substitute for individualized medical advice.

Acarbose (Precose) Medication

Roughly 0.5–0.8 percentage point HbA1c reduction vs. placebo, though magnitude varies substantially by diet pattern.

Wang JS, et al. Comparison of the hypoglycemic effect of acarbose monotherapy in patients with type 2 diabetes mellitus consuming an Eastern or Western diet: a systematic meta-analysis. Clin Ther. 2013. PMID: 23602502. https://pubmed.ncbi.nlm.nih.gov/23602502/

Albiglutide (Tanzeum (Disc.)) Medication

About 0.7–0.9 percentage point HbA1c reduction vs. placebo across the HARMONY trial program (discontinued from the US market in 2018).

Ahrén B, et al. Efficacy and safety of once-weekly GLP-1 receptor agonist albiglutide (HARMONY 1). HbA1c change -0.8% vs. placebo. PMID: 25155146. https://pubmed.ncbi.nlm.nih.gov/25155146/

Weissman PN, et al. HARMONY 4: randomised trial comparing once-weekly albiglutide and insulin glargine. PMID: 25208756. https://pubmed.ncbi.nlm.nih.gov/25208756/

Alogliptin (Nesina) Medication

About 0.4–1.0 percentage point HbA1c reduction, larger when combined with metformin or pioglitazone.

Rosenstock J, et al. Alogliptin added to insulin therapy in patients with type 2 diabetes reduces HbA1c without causing weight gain or increased hypoglycaemia. PMID: 19758359. https://pubmed.ncbi.nlm.nih.gov/19758359/

Apple cider vinegar (Apple Cider Vinegar) Supplement

More consistent evidence for lowering fasting glucose than for HbA1c specifically; GRADE evidence quality for the HbA1c outcome is rated low.

Sangouni AA, et al. The improvement effect of apple cider vinegar as a functional food on anthropometric indices, blood glucose and lipid profile in diabetic patients: a randomized controlled clinical trial. 2023. PMID: 38028980. https://pubmed.ncbi.nlm.nih.gov/38028980/

Arjmandfard D, et al. Effects of apple cider vinegar on glycemic control and insulin sensitivity in patients with type 2 diabetes: A GRADE-assessed systematic review and dose-response meta-analysis of controlled clinical trials. Front Nutr. 2025. PMCID: PMC11821484. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11821484/

Berberine (Berberine-500) Supplement

About 0.6–1.0 percentage point HbA1c reduction across pooled RCTs, alone or combined with standard therapy.

Dong H, Wang N, Zhao L, Lu F. Berberine in the Treatment of Type 2 Diabetes Mellitus: A Systemic Review and Meta-Analysis. Evid Based Complement Alternat Med. 2012;2012:591654. PMCID: PMC3478874. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3478874/

Glucose-lowering effect of berberine on type 2 diabetes: A systematic review and meta-analysis. Front Pharmacol. 2022. PMCID: PMC9709280. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9709280/

Bitter melon (Bitter Melon) Supplement

Evidence is mixed — some meta-analyses find a modest ~0.2–0.3 percentage point HbA1c reduction, others find no significant effect vs. placebo.

Peter EL, et al. meta-analysis of bitter melon extract trials in type 2 diabetes (10 studies, 1045 patients). 2019. PMID: 30385422. https://pubmed.ncbi.nlm.nih.gov/30385422/

The metabolic effect of Momordica charantia cannot be determined based on the available clinical evidence: a systematic review and meta-analysis of randomized clinical trials. 2024. PMID: 38274207. https://pubmed.ncbi.nlm.nih.gov/38274207/

Bromocriptine (Cycloset) Medication

About 0.3–0.6 percentage point HbA1c reduction vs. placebo (quick-release formulation).

Chamarthi B, et al. Quick-release bromocriptine for treatment of type 2 diabetes. HbA1c reduction 0.4–0.8% vs. placebo. PMID: 21696353. https://pubmed.ncbi.nlm.nih.gov/21696353/

Canagliflozin (Invokana) Medication

About 0.7–1.0 percentage point HbA1c reduction as monotherapy.

Stenlöf K, et al. Efficacy and safety of canagliflozin monotherapy in subjects with type 2 diabetes mellitus inadequately controlled with diet and exercise. HbA1c reduction -0.77% to -1.03%. PMC: PMC3593184. https://pmc.ncbi.nlm.nih.gov/articles/PMC3593184/

Chlorpropamide (Diabinese) Medication

About 1.0–1.5 percentage point HbA1c reduction — part of the sulfonylurea class evaluated in the landmark UKPDS trial.

UK Prospective Diabetes Study (UKPDS) Group. Intensive blood-glucose control with sulphonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes (UKPDS 33). Lancet. 1998;352(9131):837-853. PMID: 9742976. https://pubmed.ncbi.nlm.nih.gov/9742976/

Cinnamon (Ceylon) (Ceylon Cinnamon) Supplement

Small and inconsistent HbA1c reduction, roughly 0.1–0.3 percentage points; effect size and significance vary widely by meta-analysis.

The effect of cinnamon supplementation on glycemic control in patients with type 2 diabetes mellitus: An updated systematic review and dose-response meta-analysis of randomized controlled trials. 2023. PMID: 37818728. https://pubmed.ncbi.nlm.nih.gov/37818728/

Colesevelam (Welchol) Medication

About 0.3–0.6 percentage point HbA1c reduction as add-on therapy.

Colesevelam for Type 2 diabetes mellitus: an abridged Cochrane review. Placebo-corrected HbA1c reduction ~0.5%. PMID: 24024701. https://pubmed.ncbi.nlm.nih.gov/24024701/

Curcumin / turmeric (Turmeric Curcumin) Supplement

About 0.3–0.5 percentage point HbA1c reduction; larger, more consistent effects at doses of 1 g/day or more.

Curcumin/Turmeric Supplementation on Glycemic Control in Adults With Prediabetes and Type 2 Diabetes: A Systematic Review and Dose-Response Meta-Analysis. PMID: 42005325. https://pubmed.ncbi.nlm.nih.gov/42005325/

Antidiabetic and Metabolic Effects of Turmeric (Curcuma Longa) in Patients with Type 2 Diabetes Mellitus or Hyperglycemia — A Systematic Meta-Review and Meta-Analysis. PMID: 41319069. https://pubmed.ncbi.nlm.nih.gov/41319069/

Dapagliflozin (Farxiga) Medication

About 0.6–0.9 percentage point HbA1c reduction, dose-dependent.

List JF, et al. Dapagliflozin monotherapy in drug-naïve patients with diabetes: a randomized-controlled trial of low-dose range. HbA1c reduction -0.68% to -0.82%. PMID: 22776824. https://pubmed.ncbi.nlm.nih.gov/22776824/

Dulaglutide (Trulicity) Medication

About 1.0–1.5 percentage point HbA1c reduction, varying by dose and comparator across the AWARD trial program.

Wysham C, et al. Once-weekly dulaglutide versus once-daily liraglutide in metformin-treated patients with type 2 diabetes (AWARD-6). HbA1c reduction -1.42%. PMID: 25018121. https://pubmed.ncbi.nlm.nih.gov/25018121/

Jendle J, et al. A 24-week study to evaluate the efficacy and safety of once-weekly dulaglutide added on to glimepiride (AWARD-8). PMID: 26799540. https://pubmed.ncbi.nlm.nih.gov/26799540/

Efpeglenatide (Efpeglenatide) Medication

About 1.0–1.3 percentage point HbA1c reduction across the AMPLITUDE trial program; not yet FDA-approved.

Efficacy and safety of once-weekly efpeglenatide in people with suboptimally controlled type 2 diabetes: The AMPLITUDE-D, AMPLITUDE-L and AMPLITUDE-S randomized controlled trials. PMID: 37013892. https://pubmed.ncbi.nlm.nih.gov/37013892/

Empagliflozin (Jardiance) Medication

About 0.6–0.9 percentage point HbA1c reduction, dose-dependent.

Roden M, et al. Empagliflozin monotherapy with sitagliptin as an active comparator in patients with type 2 diabetes: a randomised, double-blind, placebo-controlled, phase 3 trial. PMID: 24622369. https://pubmed.ncbi.nlm.nih.gov/24622369/

Ertugliflozin (Steglatro) Medication

About 0.7–0.9 percentage point HbA1c reduction added to metformin, non-inferior to glimepiride.

Hollander P, et al. Ertugliflozin Compared with Glimepiride in Patients with Type 2 Diabetes Mellitus Inadequately Controlled on Metformin: The VERTIS SU Randomized Study. PMID: 29282633. https://pubmed.ncbi.nlm.nih.gov/29282633/

Exenatide (Short-acting) (Byetta) Medication

About 0.8–1.0 percentage point HbA1c reduction (twice-daily formulation).

Buse JB, et al. Use of twice-daily exenatide in basal insulin-treated patients with type 2 diabetes: a randomized, controlled trial. Between-group HbA1c difference -0.69%. PMID: 21138825. https://pubmed.ncbi.nlm.nih.gov/21138825/

Exenatide (Weekly) (Bydureon) Medication

About 1.3–1.5 percentage point HbA1c reduction — the once-weekly formulation outperforms twice-daily exenatide in head-to-head trials.

Drucker DJ, et al. DURATION-1: Exenatide Once Weekly Produces Sustained Glycemic Control and Weight Loss Over 52 Weeks. HbA1c reduction -2.0%. PMC: PMC2875434. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2875434/

Fenugreek seeds (Fenugreek) Supplement

About 0.5–0.6 percentage point HbA1c reduction, with considerable heterogeneity across trials.

The Effect of Fenugreek in Type 2 Diabetes and Prediabetes: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Int J Mol Sci. 2023. PMID: 37762302. https://pubmed.ncbi.nlm.nih.gov/37762302/

Ginger powder (Organic Ginger) Supplement

Reported reductions range widely (roughly 0.3 to over 1.0 percentage points) depending on the meta-analysis; more recent reviews show weaker, less consistent effects than earlier ones.

The effect of ginger supplementation on metabolic profiles in patients with type 2 diabetes mellitus: A systematic review and meta-analysis of randomized controlled trials. 2022. PMID: 35031435. https://pubmed.ncbi.nlm.nih.gov/35031435/

Glimepiride (Amaryl) Medication

About 1.0–1.5 percentage point HbA1c reduction, similar in magnitude to other second-generation sulfonylureas.

Comparison of the Efficacy of Glimepiride, Metformin, and Rosiglitazone Monotherapy in Korean Drug-Naïve Type 2 Diabetic Patients. HbA1c reduction 0.8-0.9% (this trial); sulfonylureas as a class are reported at 1.0-1.5% versus placebo in broader reviews. PMC: PMC3080564. https://pmc.ncbi.nlm.nih.gov/articles/PMC3080564/

Glipizide (Glucotrol) Medication

About 1.0–1.5 percentage point HbA1c reduction as monotherapy, similar to other sulfonylureas.

Nauck MA, et al. Efficacy and safety of the dipeptidyl peptidase-4 inhibitor sitagliptin compared with the sulfonylurea glipizide, in patients with type 2 diabetes inadequately controlled on metformin alone. PMID: 17300595. https://pubmed.ncbi.nlm.nih.gov/17300595/

Long-term randomized placebo-controlled double-blind therapeutic comparison of glipizide and glyburide. PMID: 8112188. https://pubmed.ncbi.nlm.nih.gov/8112188/

Glyburide (Diabeta, Glynase) Medication

About 1.0–1.5 percentage point HbA1c reduction as monotherapy, similar to other sulfonylureas.

Long-term randomized placebo-controlled double-blind therapeutic comparison of glipizide and glyburide. Glycemic control and insulin secretion during 15 months. PMID: 8112188. https://pubmed.ncbi.nlm.nih.gov/8112188/

UK Prospective Diabetes Study (UKPDS 33) — glibenclamide (glyburide) was one of the sulfonylureas studied. PMID: 9742976. https://pubmed.ncbi.nlm.nih.gov/9742976/

Linagliptin (Tradjenta) Medication

About 0.5–0.7 percentage point HbA1c reduction as monotherapy.

Del Prato S, et al. Effect of linagliptin monotherapy on glycaemic control and markers of β-cell function in patients with inadequately controlled type 2 diabetes: a randomized controlled trial. Placebo-corrected HbA1c change -0.69%. PMID: 21205122. https://pubmed.ncbi.nlm.nih.gov/21205122/

The effect of linagliptin on glycaemic control and tolerability in patients with type 2 diabetes mellitus: a systematic review and meta-analysis. HbA1c -0.63%. PMID: 22340363. https://pubmed.ncbi.nlm.nih.gov/22340363/

Liraglutide (Victoza) Medication

About 1.0–1.3 percentage point HbA1c reduction, larger than exenatide twice-daily in a head-to-head trial (LEAD-6).

Buse JB, et al. LEAD-6: liraglutide 1.8 mg once daily vs. exenatide 10 mcg twice daily. HbA1c reduction -1.12% vs. -0.79%. Cited via meta-analysis PMID: 26662611. https://pubmed.ncbi.nlm.nih.gov/26662611/

Lixisenatide (Adlyxin) Medication

About 0.5–0.9 percentage point HbA1c reduction across the GetGoal trial program.

Fonseca VA, et al. GetGoal-Mono: HbA1c reduction 0.66% and 0.54% vs. placebo, across the GetGoal program (0.4–1.0% range reported). Reviewed in: The Clinical Development Program of Lixisenatide. PMC: PMC4269639. https://pmc.ncbi.nlm.nih.gov/articles/PMC4269639/

Metformin (Glucophage) Medication

About 0.9–1.3 percentage point HbA1c reduction as monotherapy — one of the largest effect sizes among oral agents.

Hirst JA, Farmer AJ, Ali R, Roberts NW, Stevens RJ. Quantifying the Effect of Metformin Treatment and Dose on Glycemic Control. Diabetes Care. 2012;35(2):446-454. PMID: 22275444. https://pubmed.ncbi.nlm.nih.gov/22275444/

Miglitol (Glyset) Medication

About 0.5–0.8 percentage point HbA1c reduction as monotherapy, similar in class to acarbose.

Johnston PS, et al. The efficacy and safety of miglitol therapy compared with glibenclamide in patients with NIDDM inadequately controlled by diet alone. HbA1c fell 0.78% with miglitol. PMID: 9135927. https://pubmed.ncbi.nlm.nih.gov/9135927/

Nateglinide (Starlix) Medication

About 0.5–0.8 percentage point HbA1c reduction, generally smaller than repaglinide within the meglitinide class.

Gerich J, et al. Nateglinide alone or with metformin safely improves glycaemia to target in patients up to an age of 84. HbA1c fell 0.67-0.83%. PMID: 15287927. https://pubmed.ncbi.nlm.nih.gov/15287927/

Pioglitazone (Actos) Medication

About 0.8–1.5 percentage point HbA1c reduction, comparable to rosiglitazone.

Richter B, et al. Comparative effectiveness of pioglitazone and rosiglitazone in type 2 diabetes, prediabetes, and the metabolic syndrome: a meta-analysis. Pioglitazone HbA1c reduction -0.99% vs. placebo. PMID: 18220664. https://pubmed.ncbi.nlm.nih.gov/18220664/

Pramlintide (Symlin) Medication

About 0.3–0.7 percentage point HbA1c reduction as adjunct to insulin, alongside modest weight loss.

Hollander P, et al. Pramlintide as an adjunct to insulin therapy improves long-term glycemic and weight control in patients with type 2 diabetes: a 1-year randomized controlled trial. Diabetes Care. 2003. PMID: 12610038. https://pubmed.ncbi.nlm.nih.gov/12610038/

Singh-Franco D, et al. The effect of pramlintide acetate on glycemic control and weight in patients with type 2 diabetes mellitus and in obese patients without diabetes: a systematic review and meta-analysis. Diabetes Obes Metab. 2011. PMID: 21199269. https://pubmed.ncbi.nlm.nih.gov/21199269/

Repaglinide (Prandin) Medication

About 1.0–1.5 percentage point HbA1c reduction — one of the larger effect sizes among oral secretagogues.

Goldberg RB, et al. A randomized placebo-controlled trial of repaglinide in the treatment of type 2 diabetes. Between-group HbA1c difference -1.7%. PMID: 9802740. https://pubmed.ncbi.nlm.nih.gov/9802740/

Rosiglitazone (Avandia) Medication

About 0.8–1.5 percentage point HbA1c reduction, comparable to pioglitazone (largely withdrawn from use in many countries over cardiovascular safety concerns).

Richter B, et al. Comparative effectiveness of pioglitazone and rosiglitazone in type 2 diabetes, prediabetes, and the metabolic syndrome: a meta-analysis. Rosiglitazone HbA1c reduction -0.92% vs. placebo. PMID: 18220664. https://pubmed.ncbi.nlm.nih.gov/18220664/

Saxagliptin (Onglyza) Medication

About 0.6–0.8 percentage point HbA1c reduction as monotherapy in treatment-naive patients.

Rosenstock J, et al. Effect of saxagliptin monotherapy in treatment-naïve patients with type 2 diabetes. HbA1c reductions -0.61% to -0.71% vs. placebo -0.26%. PMID: 19650754. https://pubmed.ncbi.nlm.nih.gov/19650754/

Semaglutide (Injectable) (Ozempic/Wegovy) Medication

About 1.5–1.8 percentage point HbA1c reduction added to metformin, dose-dependent — among the larger effect sizes for GLP-1 receptor agonists.

Sorli C, et al. Efficacy and safety of once-weekly semaglutide monotherapy versus placebo in patients with type 2 diabetes (SUSTAIN 1). PMID: 28110911. https://pubmed.ncbi.nlm.nih.gov/28110911/

Ahmann AJ, et al. Once-Weekly Semaglutide Reduces HbA1c and Body Weight in Patients with Type 2 Diabetes Regardless of Background Common OAD: a Subgroup Analysis from SUSTAIN 2-4 and 10 (metformin +/- sulfonylurea background). PMID: 32193837. https://pubmed.ncbi.nlm.nih.gov/32193837/

Frías JP, et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes (SURPASS-2) — semaglutide 1 mg comparator arm. PMID: 34170647. https://pubmed.ncbi.nlm.nih.gov/34170647/

Semaglutide (Oral) (Rybelsus) Medication

About 0.9–1.4 percentage point HbA1c reduction across the PIONEER phase 3 program, dose-dependent (3/7/14 mg).

Aroda VR, Rosenstock J, et al. PIONEER 1: Randomized Clinical Trial of the Efficacy and Safety of Oral Semaglutide Monotherapy in Comparison With Placebo in Patients With Type 2 Diabetes. Diabetes Care. 2019;42(9):1724-1732. Placebo-adjusted HbA1c reduction -0.7% (3mg) to -1.4% (14mg). PMC: PMC6771751. https://pmc.ncbi.nlm.nih.gov/articles/PMC6771751/

Sitagliptin (Januvia) Medication

About 0.6–0.8 percentage point HbA1c reduction as monotherapy.

Aschner P, et al. Efficacy and safety of the dipeptidyl peptidase-4 inhibitor sitagliptin as monotherapy in patients with type 2 diabetes mellitus. Placebo-subtracted HbA1c reduction -0.60% and -0.48%. PMID: 17001471. https://pubmed.ncbi.nlm.nih.gov/17001471/

Tirzepatide (Mounjaro) Medication

About 1.8–2.3 percentage point HbA1c reduction — among the largest of any agent in the calculator, consistent with its dual incretin mechanism.

Frías JP, et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes (SURPASS-2). N Engl J Med. 2021;385(6):503-515. PMID: 34170647. https://pubmed.ncbi.nlm.nih.gov/34170647/

Tolazamide (Tolinase) Medication

Older first/second-generation sulfonylurea; direct HbA1c trial data is sparse (most trials predate HbA1c as a standard endpoint and used fasting glucose). Assumed broadly consistent with the ~1.0–1.5 percentage point sulfonylurea class effect.

Landstedt-Hallin L, et al. Combined therapy of insulin and tolazamide decreases insulin requirement and serum triglycerides. PMID: 3605188. https://pubmed.ncbi.nlm.nih.gov/3605188/

Tolbutamide (Orinase) Medication

Older first-generation sulfonylurea; direct HbA1c trial data is sparse (most trials predate HbA1c as a standard endpoint and used fasting glucose). Assumed broadly consistent with the ~1.0–1.5 percentage point sulfonylurea class effect.

Glipizide versus tolbutamide, an open trial. Effects on insulin secretory patterns and glucose concentrations. PMID: 6988265. https://pubmed.ncbi.nlm.nih.gov/6988265/

Viscous soluble fiber (e.g. psyllium, β-glucan) (Psyllium Husk) Supplement

About 0.2–0.5 percentage point HbA1c reduction; larger effects seen with psyllium specifically and with longer (6+ week) use.

Effect of viscous soluble dietary fiber on glucose and lipid metabolism in patients with type 2 diabetes mellitus: a systematic review and meta-analysis on randomized clinical trials. Front Nutr. 2023. PMCID: PMC10500602. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10500602/

The effect of psyllium on fasting blood sugar, HbA1c, HOMA-IR, and insulin control: a GRADE-assessed systematic review and meta-analysis of randomized controlled trials. 2024. PMID: 38844885. https://pubmed.ncbi.nlm.nih.gov/38844885/