Prøphet
“Rage, rage against the dying of the light”
- Joined
- Dec 28, 2024
- Posts
- 18,677
- Reputation
- 31,129
A new study on hair-loss drug RU58441 was released on 19 August, 2026.
Investigation Into the Metabolism and Elimination Behavior of RU 58841, and Its Influence on the Steroid Profile in Humans
Found here
It was first published on 19 August 2026, by researchers associated with the German Sport University Cologne and the European Monitoring Center for Emerging Doping Agents. Its primary purpose was not hair loss treatment or safety testing. The researchers wanted to understand:
1. What RU58841 turns into in the human body.
2. Whether topical RU58841 reaches systemic circulation.
3. How long RU58841/metabolites can be detected.
4. Whether it alters the urinary steroid profile used in anti-doping testing.
The participants
One especially interesting detail: the product wasn't actually 5%
The researchers bought an RU58841 hair serum from an internet supplier.
It was labelled as containing 50 mg/mL (5%) RU58841, but when they tested it, they estimated the actual RU58841 concentration at approximately 30 mg/mL.
They reported no other drugs detected in their analysis. This is interesting because it provides a real example of the quality-control problem with the grey market: the product apparently did not contain the labelled concentration.
So they applied 1 mL, which corresponded to approximately 30 mg of RU58841.
Did it actually get into the blood?
Yes. And this is the study's biggest finding.
They used dried blood spots (DBS) collected repeatedly after application. RU58841 itself was detected in the blood samples of all six participants.
According to the paper:
That is much stronger evidence than merely saying, “maybe a tiny amount crosses the skin.”
The researchers explicitly concluded that topical administration resulted in systemic availability and therefore has the potential to produce systemic effects.
But an important caveat about that 5 μg/mL number
The study was designed primarily as an analytical/metabolism study, not a rigorous pharmacokinetic trial.
The authors' normal validated blood calibration range only went up to 200 ng/mL, so the approximately 5 μg/mL peak exceeded that range. They created an additional calibration curve to estimate the higher concentrations, and the authors did not present this as a definitive full pharmacokinetic characterization.
So I would not interpret the study as giving us a precise, clinically established "normal RU58841 blood concentration."
But qualitatively, the result is quite clear:
What happened to it?
The parent RU58841 was detected in blood, while multiple metabolites were found in urine.
The researchers identified several metabolic pathways, including:
Five metabolites were detected in vivo in urine. Some of the metabolites remained detectable for a surprisingly long time—up to approximately 213 hours in the sampling data.
This is useful because it demonstrates that humans are not simply applying RU58841 and having it remain entirely confined to the scalp.
The body is absorbing it, circulating it, metabolizing it, and excreting metabolic products.
Did they find hormonal disruption?
Not in the particular test they performed.
They examined the urinary steroid profile, including parameters used in the Athlete Biological Passport. After this single 30 mg application, they did not observe alterations in those steroid-profile markers in the six participants.
But this absolutely doesn't mean “RU58841 has no systemic hormonal effects.”
The authors themselves point out that RU58841 is generally intended to be used repeatedly and that chronic daily use could potentially produce cumulative or steady-state effects, which this experiment did not investigate.
What the study does not tell us
This is probably the most important part for someone trying to interpret it sensibly.
It does not tell us:
And with only six participants, it couldn't realistically detect uncommon adverse events anyway.
Honestly, I think this study changes the RU58841 discussion in a meaningful way.
Now we have direct human evidence that a single topical scalp application can produce measurable systemic exposure in every participant in this tiny study. That does not establish that this exposure is harmful. But it makes the blanket claim that RU58841 “only works locally and doesn't go systemic” difficult to defend.
At the same time, it also did not reveal an obvious acute endocrine signal in the steroid-profile measurements after one dose.
Investigation Into the Metabolism and Elimination Behavior of RU 58841, and Its Influence on the Steroid Profile in Humans
Found here
It was first published on 19 August 2026, by researchers associated with the German Sport University Cologne and the European Monitoring Center for Emerging Doping Agents. Its primary purpose was not hair loss treatment or safety testing. The researchers wanted to understand:
1. What RU58841 turns into in the human body.
2. Whether topical RU58841 reaches systemic circulation.
3. How long RU58841/metabolites can be detected.
4. Whether it alters the urinary steroid profile used in anti-doping testing.
The participants
- 6 healthy male volunteers
- Ethics approval was obtained from the German Sport University Cologne.
- Each participant received a single topical administration to the scalp.
- The intended administered amount was 30 mg of RU58841.
- Blood and urine were then sampled repeatedly for roughly 7–10 days.
One especially interesting detail: the product wasn't actually 5%
The researchers bought an RU58841 hair serum from an internet supplier.
It was labelled as containing 50 mg/mL (5%) RU58841, but when they tested it, they estimated the actual RU58841 concentration at approximately 30 mg/mL.
They reported no other drugs detected in their analysis. This is interesting because it provides a real example of the quality-control problem with the grey market: the product apparently did not contain the labelled concentration.
So they applied 1 mL, which corresponded to approximately 30 mg of RU58841.
Did it actually get into the blood?
Yes. And this is the study's biggest finding.
They used dried blood spots (DBS) collected repeatedly after application. RU58841 itself was detected in the blood samples of all six participants.
According to the paper:
- Levels rose relatively quickly.
- Maximum concentrations occurred within roughly the first 12 hours.
- The highest observed concentration was approximately 5 μg/mL.
- Concentrations fell toward baseline by around 36 hours.
- Very low-level detection persisted in at least one participant out to 120–168 hours, depending on the analytical criterion used.
That is much stronger evidence than merely saying, “maybe a tiny amount crosses the skin.”
The researchers explicitly concluded that topical administration resulted in systemic availability and therefore has the potential to produce systemic effects.
But an important caveat about that 5 μg/mL number
The study was designed primarily as an analytical/metabolism study, not a rigorous pharmacokinetic trial.
The authors' normal validated blood calibration range only went up to 200 ng/mL, so the approximately 5 μg/mL peak exceeded that range. They created an additional calibration curve to estimate the higher concentrations, and the authors did not present this as a definitive full pharmacokinetic characterization.
So I would not interpret the study as giving us a precise, clinically established "normal RU58841 blood concentration."
But qualitatively, the result is quite clear:
What happened to it?
The parent RU58841 was detected in blood, while multiple metabolites were found in urine.
The researchers identified several metabolic pathways, including:
- oxidation/hydroxylation,
- N-dealkylation,
- further oxidation,
- glucuronidation.
Five metabolites were detected in vivo in urine. Some of the metabolites remained detectable for a surprisingly long time—up to approximately 213 hours in the sampling data.
This is useful because it demonstrates that humans are not simply applying RU58841 and having it remain entirely confined to the scalp.
The body is absorbing it, circulating it, metabolizing it, and excreting metabolic products.
Did they find hormonal disruption?
Not in the particular test they performed.
They examined the urinary steroid profile, including parameters used in the Athlete Biological Passport. After this single 30 mg application, they did not observe alterations in those steroid-profile markers in the six participants.
But this absolutely doesn't mean “RU58841 has no systemic hormonal effects.”
The authors themselves point out that RU58841 is generally intended to be used repeatedly and that chronic daily use could potentially produce cumulative or steady-state effects, which this experiment did not investigate.
What the study does not tell us
This is probably the most important part for someone trying to interpret it sensibly.
It does not tell us:
- whether daily RU58841 use is safe;
- whether chronic systemic exposure accumulates;
- whether there are cardiovascular effects;
- whether there are liver effects;
- whether there are sexual or reproductive effects;
- whether systemic androgen-receptor antagonism occurs at clinically meaningful levels;
- what happens at 50 mg, 100 mg, or higher daily doses;
- whether different vehicles dramatically change absorption;
- how much absorption varies between people;
- whether damaged/irritated scalp changes absorption.
And with only six participants, it couldn't realistically detect uncommon adverse events anyway.
Honestly, I think this study changes the RU58841 discussion in a meaningful way.
Now we have direct human evidence that a single topical scalp application can produce measurable systemic exposure in every participant in this tiny study. That does not establish that this exposure is harmful. But it makes the blanket claim that RU58841 “only works locally and doesn't go systemic” difficult to defend.
At the same time, it also did not reveal an obvious acute endocrine signal in the steroid-profile measurements after one dose.
Last edited:
dnr
