IGF-1 and bodybuilding — the history of an underground drug

The anabolic effects of growth hormone are largely not GH doing anything directly. They are IGF-1.

That realization — which was emerging simultaneously in academic endocrinology and in the underground pharmacology of competitive athletics — is the hinge point of this entire story.

The physiology was established by researchers working in the 1970s and early 1980s on what was then called the somatomedin hypothesis. The core finding: growth hormone's growth-promoting effects on peripheral tissues were mediated through intermediary peptides produced in the liver. These somatomedins — later renamed insulin-like growth factors — were the molecules actually binding to receptors in muscle and bone. GH was the upstream signal. IGF-1 was the effector. When the bodybuilding community began acquiring synthetic human growth hormone in the early-to-mid 1980s, what they were acquiring was, in effect, a very expensive way to tell the liver to make more IGF-1.

Once that relationship was understood, the obvious next step — for researchers and for underground pharmacologists alike — was to ask whether you could skip the intermediary and deliver IGF-1 directly.

The first synthetic IGF-1 preparations to reach athletic underground markets came from animal sources and early recombinant production in the late 1980s and early 1990s. Recombinant human IGF-1 was being produced in pharmaceutical research settings — Genentech and others were investigating it — and the same supply chains and gray-market networks that had distributed synthetic GH began distributing research-grade IGF-1. The early users were competitive bodybuilders and, increasingly, strength athletes in power sports. The effects reported — rapid recovery, muscle fullness, an anabolic potency that complemented steroid cycles differently than GH did — spread through the competitive community at the speed of locker-room intelligence.

The practical problem with native IGF-1, which became apparent quickly, was that it didn't work very well.

The binding protein issue that modern researchers understand clearly was encountered empirically before anyone in the athletic community had a mechanistic explanation for it. Users reported inconsistent effects. The compound was expensive and degraded quickly. Dosing was difficult because subcutaneous absorption varied and the peptide's half-life — minutes, when unbound — meant that the window of activity was brief. Some users reported hypoglycemic episodes from the insulin-pathway crossover activity, which was alarming. The early underground experience with native IGF-1 was characterized by high cost, unpredictable results, and an unclear risk profile — none of which discouraged continued use, but all of which created demand for something better engineered.

That demand was met by IGF-1 LR3 in the mid-1990s.

IGF-1 LR3 had been developed as a research tool — specifically for cell biology experiments where researchers needed an IGF-1 analog that would remain free and active in culture media without being sequestered by binding proteins. It was not developed for human use. It was not going through any clinical development pipeline. It was manufactured by research biochemical suppliers, sold as a research reagent, and within a few years of its commercial availability, it had found its way into the same underground distribution networks that supplied the competitive bodybuilding community. The athletes who encountered it found what the cell biologists already knew: the IGFBP-resistant, long-acting analog produced substantially more consistent and pronounced effects than native IGF-1. The extended half-life made dosing manageable. The systemic distribution produced whole-body anabolic signaling. LR3 became the IGF-1 product of choice in athletic underground markets and largely displaced native recombinant IGF-1 among serious users.

The arrival of IGF-1 DES followed as a counterpoint — the localization hypothesis attracting athletes who believed they had specific muscle groups that were lagging and could be brought forward with targeted local injections. The logic was sound in principle, the execution difficult in practice, and DES occupied a smaller niche alongside LR3 rather than displacing it.

Mechano Growth Factor arrived later, in the early 2000s, following Goldspink's UCL publications on the exercise-induced splice variant. The research-to-underground-market pipeline had become efficient enough by then that a published finding about a novel IGF-1 variant with satellite-cell-activating properties translated into commercially available synthetic peptide within a few years of the original papers. MGF and later PEGylated MGF were added to the toolkit of athletes already using LR3, occupying a complementary rather than competing role.

The doping enforcement picture followed its own trajectory. The World Anti-Doping Agency added IGF-1 to its prohibited list — eventually in its various forms including the analogs — and detection methods were developed, though detecting exogenous IGF-1 against the background of endogenous IGF-1 remains analytically challenging. Elite athletes in tested sports either stopped using it or became more careful about clearance times. The untested strength and physique sports continued largely without interruption. IGF-1 analogs today are on WADA's prohibited list as anabolic agents, which means their use constitutes doping in any sport under WADA's authority regardless of whether detection occurs.

The contrast with Mecasermin — the FDA-approved recombinant native IGF-1 sold as Increlex — is worth dwelling on because it illustrates how the same molecule can occupy completely different regulatory and ethical spaces depending on context. Mecasermin is approved for treating severe primary IGF-1 deficiency in children with short stature — a specific, rare pediatric condition where the IGF-1 gene or GH receptor is non-functional and the child cannot generate IGF-1 endogenously. These are children with documented deficiency, under pediatric endocrinologist supervision, with documented growth outcomes. The approval pathway was rigorous. The indication is narrow. The alternative for these children — not treating — means significant lifelong consequences from impaired growth. That clinical calculus is nothing like the calculus of a competitive bodybuilder seeking pharmacological advantage, and treating the existence of Mecasermin as legitimizing non-approved analog use in athletes is a category error that the underground literature sometimes makes.

The harm reduction conversation that developed in athletic communities over the decades of IGF-1 analog use focused heavily on the most immediately apparent risk: hypoglycemia. IGF-1 activates insulin pathway signaling — the IGF-1 receptor and insulin receptor share homology and crossreact — and high-dose IGF-1 LR3 produces blood glucose lowering that can range from mild and manageable to severe if nutrition timing is wrong. The community developed protocols: eat fast-digesting carbohydrates around injections, never inject fasted, have glucose available. These harm reduction practices were developed empirically and passed through community channels, not medical oversight.

The longer-horizon risks received less systematic community attention. The organomegaly concern — that chronic supraphysiological IGF-1 signaling drives hypertrophy not just in skeletal muscle but in cardiac muscle and internal organs — was discussed but often minimized as theoretical, a risk associated with acromegaly but not with the cycle lengths and doses used in athletics. Whether that minimization was accurate or simply a product of insufficient follow-up time is not established. The physiological truth is that the heart has abundant IGF-1 receptors, that cardiac hypertrophy from chronic IGF-1 pathway stimulation is documented in GH excess conditions, and that the doses and durations in athletic use were not monitored in any systematic way.

The cancer risk conversation developed more slowly and remains contested. Endogenous IGF-1 levels in the high-normal range are associated in large epidemiological studies with modestly elevated incidence of several cancers. The mechanism is logical: IGF-1 receptor signaling through the PI3K/Akt pathway promotes cell survival and proliferation and inhibits apoptosis — the cellular processes that malignancy exploits. Whether exogenous IGF-1 analog use, typically in cycles rather than continuous use, in younger adults, adds meaningfully to cancer risk is a question that has not been studied. The community's response to this uncertainty has ranged from dismissal to genuine concern among users with family history of IGF-1-responsive cancers, particularly prostate.

What the history of IGF-1 in bodybuilding actually is, stripped of both the performance mythology and the worst-case catastrophizing, is a story about a research compound that was co-opted into performance use because the mechanism was compelling and the regulatory vacuum was real. The research peptide market that supplies IGF-1 LR3, DES, MGF, and PEG-MGF today operates in a gray zone — these compounds can be sold as research chemicals for in vitro and laboratory use, and the legal fiction of "not for human use" governs their sale while their primary purchasers are overwhelmingly humans intending to use them. That gray zone has persisted for three decades because the FDA has not taken systematic enforcement action against research peptide suppliers, because the compounds are not scheduled controlled substances, and because the harm profile — while real — has not produced the visible acute crisis that typically drives regulatory response.

The gap between the approved IGF-1 product (Mecasermin, for a rare pediatric condition) and the extensive underground use of engineered IGF-1 analogs in athletes represents one of the larger disconnects in modern performance pharmacology — a wide gulf between what the clinical approval process covers and what is actually circulating in competitive and recreational athletics communities. That gap has been present for thirty years and shows no clear signs of closing.