T-03
IGF-1 monitoring guide
Tesamorelin is unusual among GH-axis peptides in having its lab work written into federal labeling.
Tesamorelin is unusual among GH-axis peptides in having its lab work written into federal labeling. The label mandates two tracks: IGF-1 monitored during therapy, with discontinuation considered when elevations persist above 3 standard deviation scores, and glucose evaluated before starting and periodically during treatment. This guide explains what IGF-1 measures, the exact trial numbers behind the label's thresholds, and what happens to the lab values when treatment stops.
Worked example
Trial-calibrated expectations: on the approved 2 mg regimen, mean IGF-1 rose about 107 to 108 ng/mL by week 26 while placebo drifted (SV label, Table 3). Elevation is common enough to be the monitoring trigger: 47% of patients exceeded 2 SDS and 36% exceeded 3 SDS by week 26, appearing as early as week 13 (label 5.2). And the axis lets go when the drug stops: patients switched to placebo dropped 135 to 137 ng/mL over the next 26 weeks (label, Table 5).
Step by step
- Before starting: get baseline IGF-1 and glucose status per the label, and flag any diabetes for retinopathy surveillance.
- Ask which assay and age-adjusted IGF-1 reference range the lab uses, and keep later draws on the same assay.
- During therapy: monitor IGF-1 on the schedule the prescriber sets; the trial signal appeared as early as week 13, which is why early rechecks are common.
- Know the label's action threshold: persistent IGF-1 above 3 SDS, especially without a robust fat-reduction response, is the label's stated trigger to consider discontinuing.
- Keep glucose in the loop: periodic monitoring for new glucose intolerance or diabetes is a label instruction, not an optional extra.
- Bring symptoms to every review: edema, joint aches, carpal tunnel symptoms, and any vision changes if diabetic.
IGF-1 on and off tesamorelin, from the label and trials
| Setting | Regimen | IGF-1 result | Source |
|---|---|---|---|
| Phase 3, week 26 (label Table 3) | 2 mg SC daily | +107 and +108 ng/mL vs -15 and +3 on placebo | SV label |
| Phase 3, week 26 (label 5.2) | 2 mg SC daily | 47% above 2 SDS; 36% above 3 SDS (as early as week 13) | SV label |
| Phase 3, week 52 continuers (label 5.2) | 2 mg SC daily | 34% above 2 SDS; 23% above 3 SDS | SV label |
| Extension, switched to placebo (label Table 5) | none (post-treatment) | -137 and -135 ng/mL over 26 weeks | SV label |
| Phase 2 dose-ranging | 1 or 2 mg SC daily, 12 weeks | +48% (1 mg) and +65% (2 mg) | Falutz 2005 |
| Cognition trial (older adults) | 1 mg SC daily, 20 weeks | +117%, remaining within the physiological range | Baker 2012 |
| Non-HIV obesity trial | 2 mg SC daily, 12 months | +92 ug/L treatment effect | Makimura 2012 |
Frequently asked questions
What does IGF-1 actually measure?
The liver's integrated response to growth hormone. GH itself pulses and is hard to catch in one draw; IGF-1 stays stable across the day, so labels use it as the axis readout. Tesamorelin's label uses it as both the effect marker and the safety brake: monitor during therapy.
IGF-1 (insulin-like growth factor 1) is produced mainly by the liver in response to growth hormone and mediates part of GH's signaling; the tesamorelin label notes that some but not all GH effects run through IGF-1. Because tesamorelin releases GH in pulses, a random GH level is nearly meaningless, while IGF-1 integrates exposure over time.
That is why the label makes IGF-1 the monitoring anchor: tesamorelin stimulates GH and increases IGF-1 and IGFBP-3, the effects of prolonged IGF-1 elevation are unknown, and the label directs monitoring during therapy with discontinuation considered for persistent elevations above 3 SDS. It is a proxy and a brake, not a scoreboard.
Is a higher IGF-1 level better?
No. On tesamorelin's label, high IGF-1 is a discontinuation trigger, not a goal: consider stopping if it persists above 3 SDS, particularly without a robust efficacy response. Somatropin labels likewise cut dose when IGF-1 exceeds the age-adjusted range. Above range means a dose conversation.
No, and tesamorelin's label is unusually direct about it: the effects of prolonged IGF-1 elevation are unknown, and persistent elevation above 3 SDS is the stated trigger to consider discontinuing, particularly when the fat-reduction response is not robust. In the trials this was not a rare edge case: 36% of patients crossed 3 SDS by week 26.
The convention holds across the GH axis: somatropin labels titrate dose against serum IGF-1 and direct decreases when it exceeds the age- and gender-specific normal range. No study ties pushing IGF-1 above age-normal to better outcomes in any tesamorelin population, while the GH literature in healthy older adults links stronger axis stimulation to edema, arthralgia, carpal tunnel syndrome, and glucose problems. If a draw comes back above range, the evidence-consistent response is a prescriber conversation, not celebration.
Why does tesamorelin require glucose monitoring?
Because GH raises blood sugar. In the trials, 5% of tesamorelin patients vs 1% on placebo reached diabetic-range HbA1c by week 26 (hazard ratio 3.3). The label says evaluate glucose before starting, monitor periodically during, and watch retinopathy in patients with diabetes.
Growth hormone opposes insulin, so a drug that raises GH raises the glucose question, and tesamorelin's trials quantified it: 5% of treated patients versus 1% on placebo developed HbA1c of 6.5% or higher by week 26, an intent-to-treat hazard ratio of 3.3 (CI 1.4 to 9.6). In the Stanley 2014 trial, fasting glucose rose early (about +7 mg/dL treatment effect at 2 weeks) and was no longer significantly different by 6 months, and the 12-month NAFLD trial found no HbA1c difference at 12 months; the label still requires vigilance.
The label's instructions: evaluate glucose status before initiating, monitor all patients periodically to catch new glucose intolerance or diabetes, consider discontinuing in patients who develop it without a clear efficacy response, and monitor diabetic patients regularly for development or worsening of retinopathy. Anyone with prediabetes walking into a tesamorelin conversation should walk in knowing these numbers.
What happens to IGF-1 when tesamorelin stops?
It falls back. In the blinded extensions, patients switched to placebo dropped 135 to 137 ng/mL over 26 weeks while continuers held most of their elevation. The visceral fat regain runs on the same clock, which is why stopping is a planned decision, not an afterthought.
The extension tables answer this precisely: patients re-randomized from tesamorelin to placebo saw IGF-1 fall -137 ng/mL (Study 1) and -135 ng/mL (Study 2) over the following 26 weeks, versus -59 and -25 among those continuing. The axis returns to its own baseline once the daily GHRH signal stops.
The clinical shadow of that curve is the fat regain measured on the same visits: +22% and +16% VAT among switchers. Together they define what tesamorelin is: a maintained signal with maintained monitoring, whose biology and benefit both unwind on discontinuation. A stop should be planned with the prescriber, with a final IGF-1 and glucose check closing the loop.
Tools: educational calculators and references only.