IGF-1 LR3

Long R3 IGF-1 · B-tier (Dr. Alex Tatem) · Preclinical evidence

One of the few compounds in this space that directly stimulates muscle growth, but it has never been through human trials and can crash blood sugar.

Dr. Tatem’s take

B-tier. It’s the only “new-wave” peptide that genuinely builds muscle, but it “can actually cause drops in blood sugar”, and real growth hormone is better and cheaper.

In Dr. Tatem’s tier list

• IGF-1 is how growth hormone actually works — GH and every secretagogue are ultimately trying to raise IGF-1. So why not give IGF-1 directly?
• Native IGF-1 has a very short half-life; LR3 (“long release”) is the modified form that lasts long enough to be practical.
• It’s “the only one out of these new generation of peptides that will actually stimulate hypertrophy.”
• Unlike GH (which raises blood sugar), IGF-1 LR3 “can actually cause drops in blood sugar” — sweats and low-sugar symptoms, acting a bit like insulin.
• Verdict: B tier. Real effect, strong literature on IGF-1 itself, but growth hormone is now cheaper and more available and remains the gold standard.

History & background

IGF-1 (insulin-like growth factor 1) was characterized in the 1970s as the “somatomedin” that carries out most of growth hormone’s effects on tissue. Long R3 IGF-1 is an engineered analog (arginine at position 3 plus a 13-amino-acid extension) designed for cell-culture manufacturing because it binds poorly to IGF-binding proteins and stays active longer.

It has never been through human trials. The only approved IGF-1 drug is mecasermin (Increlex, 2005) for severe primary IGF-1 deficiency in children, whose label warns of hypoglycemia.

Benefits

• Directly drives muscle-cell growth (lab and animal data).

Risks

• Low blood sugar (hypoglycemia), which can be severe.
• Theoretical: could promote the growth of existing tumors.
• No human safety data at all.

Dosing protocols (informational, labeled by evidence)

• Community (bro science): Community protocol — 20–80 mcg (start 20–30 mcg, raise 10–20 mcg/wk), SubQ, Daily, 4–6 wk on, 3–6 wk off
• Clinical trial / label: Reference only: mecasermin (Increlex) label – a different molecule — 0.04–0.08 mg/kg, titrate by 0.04 mg/kg to max 0.12 mg/kg, SubQ, Twice daily, within 20 min of a meal, Chronic (pediatric primary IGF-1 deficiency)

Status: Never tested in humans. It’s a cell-culture lab reagent. The approved relative, mecasermin, is prescribed only for severe IGF-1 deficiency.

Grade and commentary: Dr. Alex Tatem. Watch: The Truth About Popular Peptides (What Works, What’s Overhyped) | Peptide Tier List pt.1. Subscribe: @DrAlexTatem.