How Semaglutide Affects IGF-1

Semaglutide does not directly bind the IGF-1 receptor or the growth hormone axis. Its effects on the GH/IGF-1 axis are indirect and mediated by changes in body composition, insulin signalling, and hepatic IGFBP production.

1. IGFBP-1 elevation: Insulin normally suppresses hepatic IGFBP-1 synthesis. Semaglutide-driven improvements in insulin sensitivity mean lower fasting insulin, less IGFBP-1 suppression, and modestly higher circulating IGFBP-1. Higher IGFBP-1 binds free IGF-1 and reduces bioavailable IGF-1.
2. Total IGF-1 preserved: Hepatic IGF-1 synthesis is primarily driven by GH pulses, and semaglutide does not meaningfully alter GH pulsatility at label doses. Total IGF-1 stays essentially flat in most human studies.
3. Weight loss context: Aggressive caloric restriction can lower total IGF-1 (a hallmark of the longevity phenotype). Semaglutide-driven weight loss occurs alongside this, so the two effects can be difficult to separate in short trials.
4. Growth-versus-longevity axis: Low IGF-1 is one of the best-replicated biomarkers of exceptional longevity in humans (Milman et al., 2014, Aging Cell, PMID 24618355). Centenarians are enriched for IGF-1 receptor loss-of-function variants. Semaglutide's shift toward higher IGFBP-1 with preserved total IGF-1 sits in the direction of the longevity phenotype without collapsing the axis you need for tissue repair.

For contrast, MK-677 and GH secretagogues push the axis in the opposite direction, raising IGF-1 substantially and driving insulin resistance, which is the growth-versus-longevity tradeoff in the other direction.

Standard doses (1.0-2.4 mg per week):

• Total IGF-1: essentially unchanged in most human studies (typical variation +/- 10% from baseline, no systematic direction)
• IGFBP-1: modest increase of 20-40% from baseline over 12-24 weeks
• Bioavailable IGF-1 (calculated): may nudge down 5-10%
• IGF-1 z-score (age and sex adjusted): stable

Microdose (0.25 mg per week):

• Effects on the IGF-1 axis at cruise microdose are unstudied in controlled trials
• Direction likely similar but smaller magnitude, given that the mechanism is indirect via insulin sensitivity

In combination with AAS:

• AAS use raises IGF-1 by 10-30% at typical doses, an effect largely independent of semaglutide
• If both are running concurrently, expect IGF-1 to reflect the AAS signal, not the GLP-1 signal
• Semaglutide will not blunt the AAS-driven IGF-1 rise at label doses

Discontinuation:

• IGFBP-1 returns to pre-treatment level within weeks of stopping
• Total IGF-1 remains stable throughout

Baseline: total IGF-1 and IGFBP-3 before starting. Draw fasting to minimise post-prandial variation. IGF-1 z-score adjusted for age and sex is more informative than the absolute number in isolation.

On treatment: recheck at 12 and 24 weeks. Track direction rather than expecting a specific number. If IGF-1 stays flat or drifts slightly down while insulin sensitivity improves (HOMA-IR falling), the axis is behaving as expected.

Concurrent AAS or GH use: IGF-1 will reflect those signals primarily. Semaglutide will not confound the AAS-driven or GH-driven IGF-1 elevation at typical doses. If IGF-1 rises substantially on semaglutide alone with no AAS or GH, look for another cause: recent injury, aggressive training block, or exogenous GH exposure.

Red flag: an unexplained large drop in IGF-1 (more than 30% from baseline) on semaglutide monotherapy is unusual and warrants investigation. Consider hepatic dysfunction, aggressive caloric restriction beyond the drug's appetite effect, or GH deficiency.

Do not force IGF-1 in either direction: the semaglutide effect is small and largely useful. Trying to drive IGF-1 lower with additional interventions (aggressive restriction, sirolimus, metformin) risks overshooting the growth-versus-longevity tradeoff into territory where tissue repair and lean mass preservation suffer.

Stack considerations:

• With GH secretagogues (MK-677, CJC-1295, ipamorelin): IGF-1 will reflect the secretagogue signal. Semaglutide does not neutralise the secretagogue effect.
• With TRT: TRT raises IGF-1 modestly. Semaglutide will not blunt this. If bloodwork shows IGF-1 above age-adjusted normal range on TRT + semaglutide, look at the TRT side.

Longevity motive: if you are running semaglutide specifically for the longevity signal from Feng et al. (2026, Nature), IGF-1 is a reasonable secondary tracker but not a primary readout. hs-CRP, HOMA-IR, cystatin-C-based eGFR and ApoB are more informative for the longevity claim.

Further reading: How semaglutide extended lifespan 12% in old female mice. How MK-677 raises IGF-1 and blood sugar.