IGF-1, HGH, and tesamorelin: what to know

This article is educational. It does not constitute medical advice, and no part of it should be read as a recommendation to start, stop, or adjust any medicine or peptide. Decisions of that kind belong with a clinician who has access to your full health history.

A post on r/peptides recently described someone two months into HGH use who had an IGF-1 result of 159 ng/mL and no baseline to compare it to. The question: is that low? Should the dose go up? Or is it time to switch to tesamorelin? The short answer is that 159 ng/mL cannot be evaluated without knowing the person's age, sex, and the assay used. The longer answer requires understanding what IGF-1 actually measures and how each of the two approaches to the GH axis works.

What IGF-1 is and why the number alone is not enough

Insulin-like growth factor 1 is a peptide hormone produced mainly in the liver in response to growth hormone (GH) signals from the pituitary gland. Clinicians use it as a proxy for GH status because GH itself pulses unpredictably throughout the day, making a single blood draw nearly meaningless, while IGF-1 stays relatively stable across the day and reflects the cumulative GH signal over several hours. A 2014 multicenter study in the Journal of Clinical Endocrinology and Metabolism that established automated immunoassay reference intervals found that IGF-1 levels fall consistently with age and that women show lower concentrations than men across the adult lifespan^[4].

What that means practically: a result of 159 ng/mL is in a normal range for a 50-year-old but would sit well below the typical mid-range for a 25-year-old on the same assay. Without a baseline drawn before starting any GH-axis agent, and without age- and sex-stratified reference intervals from the laboratory that ran the test, the number is uninterpretable as a signal of treatment response.

How recombinant HGH raises IGF-1

Recombinant human growth hormone (rhGH, or HGH as it is commonly called online) is an injectable form of the full GH protein. It bypasses the hypothalamic-pituitary axis and delivers GH directly into the bloodstream. The liver then converts a portion of that GH signal into IGF-1. Because the dose is fixed and external, IGF-1 rises in a relatively dose-proportional way but does so at the cost of suppressing the pituitary's own GH output over time. The pituitary reads the elevated GH signal and reduces its own secretion in response. Rheumatological and metabolic side effects including fluid retention, joint pain, and glucose dysregulation are characterised in the clinical literature on rhGH use.

How tesamorelin raises IGF-1 differently

Tesamorelin is a GHRH analogue, a synthetic version of the 44-amino-acid growth-hormone-releasing hormone the hypothalamus uses to signal the pituitary. Rather than injecting GH directly, tesamorelin tells the pituitary to release its own GH in roughly normal pulses. The liver converts that pulsatile GH into IGF-1.

In the phase-3 randomised controlled trials that supported FDA approval of tesamorelin for HIV-associated lipodystrophy, IGF-1 increased significantly in treated patients. The 2010 Falutz et al. trial in the Journal of Acquired Immune Deficiency Syndromes reported a statistically significant rise in IGF-1 in the tesamorelin group versus no change in the placebo group (P < 0.001)^[2]. The FDA label for Egrifta SV reports that in the two key 26-week studies, mean IGF-1 rose by approximately 107 to 108 ng/mL from baselines of 161 and 146 ng/mL respectively. At 26 weeks, 47 percent of tesamorelin-treated patients had IGF-1 levels greater than 2 standard deviation scores (SDS) above the age- and sex-specific mean, and 36 percent had SDS above 3^[1]. The label therefore requires periodic IGF-1 monitoring and recommends considering dose discontinuation if levels remain persistently elevated above 3 SDS.

A 2014 JAMA randomised trial by Stanley et al. examining tesamorelin in HIV patients with abdominal fat accumulation found a visceral fat reduction of 42 cm squared versus placebo at six months^[3]. These trials established tesamorelin's efficacy in its approved indication, not in off-label body-composition or anti-ageing use.

Why the mechanism difference matters for your IGF-1 reading

If someone has been using recombinant HGH for two months and gets a result of 159 ng/mL, several scenarios are consistent with that number: the baseline was already at or near 159 and the HGH has not meaningfully raised it; the baseline was lower (say, 110 ng/mL) and the HGH has produced a modest rise; or the baseline was higher and the HGH has ironically suppressed the pituitary's contribution, flattening IGF-1. None of these scenarios can be ruled out without a pre-treatment draw. The tesamorelin page on this site covers the approved indication and regulatory status in more detail.

Switching to tesamorelin as a strategy to raise IGF-1 presupposes that the pituitary is still capable of responding to GHRH stimulation, which is not guaranteed if prolonged exogenous GH use has significantly blunted pituitary output. Tesamorelin also has a narrow labelled indication (HIV-associated lipodystrophy in the US) and no marketing authorisation in the EU, EEA or UK. Off-label use for body composition or IGF-1 optimisation in otherwise healthy individuals has no published trial basis.

What a baseline would have shown

The practical value of a pre-treatment IGF-1 draw is that it anchors interpretation. If the baseline was 90 ng/mL and the post-treatment result is 159, that is a roughly 77 percent rise in a number that was already below average for the patient's age, and raises separate questions about why it started low. If the baseline was 155 ng/mL, then two months of HGH have produced essentially no measurable IGF-1 response, which has its own set of explanations ranging from dose, injection timing, and storage handling to individual variation in GH-to-IGF-1 conversion. The community advice to get baseline labs before starting any GH-axis agent is the correct approach, not a formality.

What to do with this information

This article cannot tell you what your IGF-1 of 159 ng/mL means for your specific situation. What it can tell you is that the number needs to be placed against your age- and sex-matched reference range from the testing laboratory, interpreted by a clinician who knows your history, and compared to a pre-treatment baseline if one is available. Neither increasing the HGH dose nor switching to tesamorelin is a decision that should rest on a single post-treatment number in isolation. For the regulatory picture by country for tesamorelin, see /regulation.