Peptides and blood sugar: MK-677, IGF-1 and GLP-1 hypoglycaemia risks

Why peptides move blood sugar at all

Blood sugar is set by a balance of hormones. Insulin lowers it; several others, including growth hormone and cortisol, push it up. Many peptides sold online act on this system, and they do not all push the same way. Growth hormone tends to make the body less responsive to insulin, which is why the label for somatropin warns that impaired glucose tolerance and diabetes may be unmasked and advises monitoring glucose in all patients (drug label) ¹. IGF-1, which growth hormone stimulates, has insulin-like effects and can drive glucose down ². GLP-1 drugs increase insulin release when glucose is high ³.

The result is that two peptides people often take together can have opposite effects on glucose, on different timescales. The table summarises the direction of each.

MK-677: the most studied glucose raiser

MK-677, or ibutamoren, is an oral ghrelin-receptor agonist that raises growth hormone and IGF-1. Its glucose effects are well documented. In 32 adults aged 64 to 81, 25 mg daily raised fasting glucose from 5.4 to 6.8 mmol/L within weeks (randomised trial) ⁴. In 24 obese men, eight weeks did not change fasting glucose or insulin, but glucose tolerance tests showed impairment at two and eight weeks (randomised trial) ⁵.

The longest trial gave MK-677 or placebo to healthy older adults for two years. MK-677 raised growth hormone and IGF-1 to young-adult levels and increased fat-free mass, but body weight rose by 2.7 kg against 0.8 kg on placebo, fasting glucose rose by an average of 0.3 mmol/L (5 mg/dL), and insulin sensitivity fell (randomised trial) ⁶. A rise of that size is small for an individual but meaningful for someone already near the diabetes threshold. In children with growth hormone deficiency given it for about a week, glucose and insulin did not change, a reminder that short studies can miss slow effects (human study) ⁷.

MK-677 was never approved; its development as a drug was discontinued ⁸. Anyone with prediabetes, diabetes or a strong family history should treat its glucose effect as a central risk, not a footnote.

Growth hormone, tesamorelin and other secretagogues

The same direction applies, to varying degrees, to approved drugs that raise growth hormone. Besides somatropin's warning ¹, the label for tesamorelin (EGRIFTA WR), a GHRH analogue, warns that glucose intolerance or diabetes may develop and advises evaluating glucose before and during therapy (drug label) ⁹. In trials, the effect was modest: in 50 people with HIV, fasting glucose rose by 7 mg/dL more than placebo at two weeks but fasting and two-hour glucose did not differ by six months (randomised trial) ¹⁰; over a year in people with fatty liver, fasting glucose and HbA1c did not differ from placebo (randomised trial) ¹¹; and in 53 people with type 2 diabetes, 12 weeks did not worsen diabetes control (randomised trial) ¹².

The research secretagogues sold online, such as ipamorelin, CJC-1295 and the GHRPs, have far less human data on glucose. Because they act on the same axis, a similar direction is plausible, but the size of the effect is unknown.

IGF-1: the opposite direction, and the most dangerous

IGF-1 lowers blood sugar directly. The approved form, mecasermin (INCRELEX), used for a rare childhood IGF-1 deficiency, carries a prominent warning: severe hypoglycaemia leading to seizures has been observed, so it must be given within 20 minutes of a meal or snack, glucose should be monitored while the dose is adjusted, and patients should avoid high-risk activities such as driving or exercise for two to three hours after a dose (drug label) ². If lows occur despite adequate food, the label says the dose should be reduced ². A registry analysis of treated patients found about 0.11 hypoglycaemia events per patient per year of treatment, and 0.01 serious events (registry study) ¹³.

IGF-1 LR3, a long-acting analogue sold online as a research peptide, has no human data, but in calves it lowered blood glucose and insulin (animal evidence) ¹⁴ and in fetal sheep it acutely suppressed insulin (animal evidence) ¹⁵. A product designed to last longer than natural IGF-1 and used without medical monitoring is the combination most likely to cause an unexpected low.

GLP-1 drugs: lows mostly come from combinations

GLP-1 receptor agonists lower blood sugar by boosting insulin release when glucose is raised. Their labels frame the hypoglycaemia risk around combinations. The Wegovy label says it lowers blood glucose and can cause hypoglycaemia, that the risk increases with insulin or insulin secretagogues such as sulfonylureas, and that reducing the dose of those drugs should be considered when starting it; it asks prescribers to tell all patients about the signs of low blood sugar (drug label) ³. The Mounjaro label gives the same advice for tirzepatide, and notes more hypoglycaemia in children aged 10 and over than in adults (drug label) ¹⁶.

On their own, then, GLP-1 drugs are less likely to cause dangerous lows than insulin or IGF-1, but 'less likely' is not 'never', and compounded or research versions of these drugs come without the dose control of the approved pens. Our guide to compounded and research tirzepatide covers that difference.

Why stacks are unpredictable

Online protocols often combine a growth hormone secretagogue with IGF-1 LR3, or add a GLP-1 drug for fat loss. These push glucose in opposite directions: secretagogues gradually reduce insulin sensitivity over weeks, IGF-1 can drop glucose within hours, and GLP-1 drugs lower it in response to meals. No study has combined them, so there is no way to predict the net effect for a given person. The likely pattern is the worst of both: periods of higher baseline glucose, punctuated by lows after an IGF-1 dose, especially if a meal is skipped or after exercise, the situations the mecasermin label specifically warns about ².

Our Stack Safety Analyzer flags blood-sugar effects for each compound in a combination, using the same sources as this article.

Signs to watch for

Low blood sugar can cause shakiness, sweating, a racing heart, hunger, confusion, irritability or blurred vision, and severe lows can cause seizures or loss of consciousness; the mecasermin label's warning about seizures shows how serious it can be ². Anyone using a product that can lower glucose should know these signs, have fast-acting sugar available and not drive or exercise soon after a dose. Raised glucose is quieter: thirst, passing more urine and tiredness, or nothing at all until a blood test. A fasting glucose or HbA1c test before starting and during use of any growth hormone booster is the only way to know.

Who should be most careful

• People with diabetes or prediabetes, or a strong family history: secretagogues and growth hormone can worsen glucose control, and glucose-lowering drug doses may need changing ^{1 6}.
• Anyone taking insulin or a sulfonylurea who adds a GLP-1 drug: the labels advise considering a lower dose of the other drug ^{3 16}.
• Anyone using IGF-1 in any form, especially without food or before exercise ².
• Older adults, in whom MK-677's glucose rise was documented ^{4 6}.

Questions to ask before using these peptides

• What is my fasting glucose or HbA1c now, and how will I check it while using this?
• Does this product raise or lower blood sugar, and does anything else I take do the opposite?
• Am I on insulin or a sulfonylurea, and has my prescriber been told?
• Do I know the signs of a low, and do I have fast-acting sugar with me?

The bottom line

Peptides do not have one effect on blood sugar. Growth hormone boosters such as MK-677 raise it and reduce insulin sensitivity, documented in trials over two years. IGF-1 lowers it, sometimes dangerously, which is why its approved form is given with meals and monitoring. GLP-1 drugs lower it, with the main risk of lows coming from combination with insulin or sulfonylureas. Combining these, as many online stacks do, has never been studied, and the safest assumption is that the result will be unpredictable.

Frequently asked questions

Does MK-677 raise blood sugar?

Yes. In a two-year trial in healthy older adults, fasting glucose rose by about 0.3 mmol/L and insulin sensitivity fell; in a shorter trial at 25 mg, fasting glucose rose from 5.4 to 6.8 mmol/L.

Can IGF-1 cause low blood sugar?

Yes. The approved IGF-1 drug, mecasermin, can cause severe hypoglycaemia with seizures and must be given within 20 minutes of a meal or snack.

Do GLP-1 drugs cause hypoglycaemia?

They lower blood sugar, and their labels say the risk of hypoglycaemia increases when they are combined with insulin or sulfonylureas, whose doses may need reducing.

Is it safe to stack MK-677 with IGF-1 LR3?

No study has tested the combination. They push blood sugar in opposite directions on different timescales, making the net effect unpredictable.

Should I check my blood sugar on growth hormone peptides?

Labels for approved growth hormone and tesamorelin advise monitoring glucose. A fasting glucose or HbA1c test before and during use is the only way to know your response.

Related on Grey Peptides

• MK-677 (ibutamoren)
• Mecasermin
• Stack Safety Analyzer

Sources

1. Pfizer. GENOTROPIN (somatropin) US prescribing information, Warnings and Precautions 5.4 (impaired glucose tolerance and diabetes mellitus). DailyMed version 37, effective August 4, 2026; read October 1, 2026.
2. Eton Pharmaceuticals. INCRELEX (mecasermin) US prescribing information, Dosage and Administration and Warnings and Precautions 5.1 (Hypoglycemia). DailyMed version 5, effective May 18, 2026; read October 1, 2026.
3. Novo Nordisk. WEGOVY (semaglutide) US prescribing information, Warnings and Precautions 5.4 and Drug Interactions 7.1. DailyMed version 19, effective June 18, 2026; read October 1, 2026.
4. Chapman, I. M., et al. (1996). Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. J Clin Endocrinol Metab, 81(12), 4249-57. PMID: 8954023
5. Svensson, J., et al. (1998). Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure. J Clin Endocrinol Metab, 83(2), 362-9. PMID: 9467542
6. Nass, R., et al. (2008). Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med, 149(9), 601-11. PMID: 18981485
7. Codner, E., et al. (2001). Effects of oral administration of ibutamoren mesylate, a nonpeptide growth hormone secretagogue, on the growth hormone-insulin-like growth factor I axis in growth hormone-deficient children. Clin Pharmacol Ther, 70(1), 91-8. PMID: 11452249
8. Grey Peptides encyclopedia entry for MK-677 (ibutamoren): development status (discontinued), WADA status (S2.2.4, named). Read October 3, 2026.
9. Theratechnologies. EGRIFTA WR (tesamorelin) US prescribing information, Warnings and Precautions 5.4 (glucose intolerance or diabetes mellitus). DailyMed version 2, effective July 29, 2026; read October 1, 2026.
10. Stanley, T. L., et al. (2014). Effect of tesamorelin on visceral fat and liver fat in HIV-infected patients with abdominal fat accumulation: a randomized clinical trial. JAMA, 312(4), 380-9. PMID: 25038357
11. Stanley, T. L., et al. (2019). Effects of tesamorelin on non-alcoholic fatty liver disease in HIV: a randomised, double-blind, multicentre trial. Lancet HIV, 6(12), e821-e830. PMID: 31611038
12. Clemmons, D. R., et al. (2017). Safety and metabolic effects of tesamorelin, a growth hormone-releasing factor analogue, in patients with type 2 diabetes: A randomized, placebo-controlled trial. PLoS One, 12(6), e0179538. PMID: 28617838
13. Bang, P., et al. (2023). Frequency and Predictive Factors of Hypoglycemia in Patients Treated With rhIGF-1: Data From the Eu-IGFD Registry. J Clin Endocrinol Metab, 109(1), 46-56. PMID: 37579214
14. Hammon, H., et al. (1998). Endocrine and metabolic changes in neonatal calves in response to growth hormone and long-R3-insulin-like growth factor-I administration. Biol Neonate, 73(2), 121-8. PMID: 9483305
15. White, A., et al. (2023). Attenuated glucose-stimulated insulin secretion during an acute IGF-1 LR3 infusion into fetal sheep does not persist in isolated islets. J Dev Orig Health Dis, 14(3), 353-361. PMID: 37114757
16. Eli Lilly. MOUNJARO (tirzepatide) US prescribing information, Warnings and Precautions 5.3, Drug Interactions 7.1 and Pediatric Use. DailyMed version 40, effective August 27, 2026; read October 1, 2026.

Educational information, not medical advice. Each dose in this guide names its source, an approved label or a published study. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose.