GLP-1 and fitness: separating Jeff Seidman's claims from the data

What did @jeffseidmanfitness actually say?

Jeff Seidman, introducing what he calls a "great fat loss peptide," spends his video explaining a compound he calls "Tessa Finci" — which is tesofensine, a presynaptic serotonin-noradrenaline-dopamine reuptake inhibitor. He correctly notes it is not actually a peptide. His central claims: tesofensine suppresses appetite, boosts fat oxidation at rest, dramatically increases brain-derived neurotrophic factor (BDNF), and in a Lancet clinical trial produced an average weight loss of 28 pounds over six months compared to five pounds in a placebo group. He frames this as "over 500% greater results." He also urges professional guidance, which is worth noting.

The video is generally promotional in tone and references a book by someone named Jade Campbell. There is no disclosure of financial relationships, no mention of serious cardiovascular or psychiatric risks, and the 28-pound figure is presented as if it were the headline result of a robust, replicated trial rather than a single phase 2 study from over a decade ago.

Does the science back this up?

Partially, but the framing inflates the evidence significantly. The Lancet study exists and the numbers are roughly real, but the story is more complicated than Seidman lets on.

The study he references is Astrup et al. (2008, The Lancet), a randomized phase 2 trial in 203 obese patients over 24 weeks. The highest dose group (1.0 mg/day) lost a mean of roughly 12.8 kg (about 28 lbs), versus approximately 2.2 kg in the placebo group. So the raw numbers check out. What Seidman omits: this was a small phase 2 trial, not a phase 3 confirmatory study. Tesofensine was never approved by the FDA or EMA for weight loss. Development was largely abandoned after concerns about elevated heart rate, blood pressure increases, and psychiatric side effects including insomnia and mood disturbances emerged in further study.

On BDNF: there is preclinical and some human evidence that dopaminergic and serotonergic activity can influence BDNF expression (Martinowich and Lu, 2008, Neuropsychopharmacology), but the claim that tesofensine "dramatically increases" BDNF production in humans is not backed by published clinical data specific to this compound. That is a significant overreach.

What did they get wrong (or right)?

Credit where it is due: Seidman correctly identifies that tesofensine is not a peptide, which is a more honest correction than most influencers in this space bother to make. He also recommends professional guidance and frames the compound as requiring appropriate dosing, which is responsible compared to the average biohacking content on TikTok.

What he gets wrong is more consequential. First, presenting a single phase 2 trial as if it represents settled clinical evidence is misleading. Tesofensine never cleared phase 3 trials for a reason. Second, the BDNF claim has no solid human clinical backing specific to tesofensine and reads more like mechanistic speculation dressed up as fact. Third, there is no mention of the cardiovascular signals that contributed to development being deprioritized, including increased heart rate observed in Astrup et al. itself. Fourth, calling it a "powerful tool" while omitting that it is not approved and carries real cardiovascular and psychiatric risks is a material omission for an audience that may try to source it.

What should you actually know?

Tesofensine is a real compound with real weight loss data, but it is not approved for use in the United States or European Union. The weight loss numbers from Astrup et al. are genuine, but they come from a short-term phase 2 trial that was never followed by a successful phase 3 program. That gap matters. Compounds that look impressive in small trials frequently fail to replicate or reveal new risks at scale.

The drug works through triple monoamine reuptake inhibition, similar in mechanism to some stimulant-class medications. That mechanism carries non-trivial cardiovascular implications, particularly elevated heart rate and blood pressure, which are serious considerations for anyone with metabolic syndrome, hypertension, or cardiac history. These are exactly the populations most likely to be watching weight loss content.

If you are interested in GLP-1 receptor agonists like semaglutide or tirzepatide, those are the compounds with phase 3 data, regulatory approval, and long-term cardiovascular outcome studies. Tesofensine is not in that category. Anyone sourcing it outside of a legitimate clinical research context is taking on real and poorly characterized risk.