Tesamorelin and the prescription’s small print
The strongest result concerns fat deep inside the abdomen. The people studied, the scan used and what happened after treatment all deserve space beside it.
Abdominal fat in the HIV trials
The weight column was where I first looked for an explanation of tesamorelin’s reputation. The more interesting change was inside the abdomen: in the 26-week trial of 412 adults with HIV, visceral fat fell 15.2% with tesamorelin and rose 5.0% with placebo. Visceral means the fat around internal organs. Total body weight and fat beneath the skin changed little.
That makes this an unusually specific fat-loss story. The trial concerned adults with HIV and abdominal fat accumulation, and the endpoint came from scans. Calling it a general slimming result throws away much of what made the experiment useful. I’m persuaded by the measured change in that group; extending it to everyone seeking a smaller waist asks a different question.
What does tesamorelin do?
Tesamorelin acts on the pituitary, the small gland beneath the brain, prompting release of the body’s own growth hormone. The liver then produces more insulin-like growth factor 1, usually shortened to IGF-1. A study of overnight hormone secretion in healthy men showed the response in pulses.
The molecule is a modified copy of growth hormone-releasing hormone, or GHRH. A chemical addition protects it from an enzyme that cuts up the natural signal; early laboratory and animal work tested that protection. Its makers bought the message more time. The mechanism page follows the pituitary response and a less cooperative result involving another hormone.
Is tesamorelin FDA approved?
Yes. The U.S. approval dates to November 2010 and covers reduction of excess abdominal fat in adults with HIV-associated lipodystrophy, the abnormal redistribution of fat associated with HIV and its treatment. The NIH drug-safety overview describes that approved use.
General weight loss, cosmetic use, anti-aging and fatty liver disease outside the HIV indication have no FDA approval for tesamorelin. Other uses are off-label. Compounded tesamorelin is not FDA-approved. I take the diagnosis in the approval seriously: it identifies the clinical problem for which the evidence was assembled.
Tesamorelin peptide research
This is a synthetic 44-amino-acid peptide, built from the same kinds of building blocks used in proteins. The non-clinical TH9507 paper includes animal experiments and tests in rat, dog and human plasma outside the body. Later randomized human trials addressed abdominal fat in people with HIV.
Those experiments occupy different places in the history. A result in human plasma is still a laboratory result; a dog experiment remains animal evidence. Material supplied for laboratory research also lacks the purity and potency oversight of the approved prescription product. The study doses and side effects concern the medicines and populations described in those trials.
After treatment stopped
The 52-week follow-up reported visceral fat 18% below baseline during continued treatment. Fat reaccumulated after withdrawal, beginning within weeks. I give that follow-up as much weight as the initial reduction because durability changes the significance of an apparently simple percentage.
The scan results put the visceral-fat findings alongside liver fat and CT density. For the surprisingly brief period the drug itself spends in blood, there is a separate account of tesamorelin half-life.