Comparing observation windows
The length of a trial, the persistence of a benefit and the length of a life each need their own account.
Four observation windows
I put these windows side by side because the eye is quick to turn “long-term” into an indefinite future. The NR trial observed healthy overweight adults for 8 weeks; the NMN muscle-insulin study observed prediabetic, postmenopausal women for 10 weeks. The tesamorelin program extended to 52 weeks in adults with HIV, while STEP 1 measured weight at 68 weeks in adults with overweight or obesity without diabetes.
The spans below compare observation periods only. Different substances, populations and outcomes prevent a ranking of efficacy or safety from these lengths. A longer bar supplies more time within that study, while the measured question still determines what was learned.
Results and maintenance questions
| Research | Result in the people or animals studied | The maintenance question |
|---|---|---|
| NAD+ precursors | NR raised whole-blood NAD+ through an 8-week trial; NMN improved walking distance in a 60-day trial. | Does a useful change persist, and does it alter later illness? |
| MOTS-c | Administered MOTS-c improved mouse running, grip and gait. | Human treatment benefit and its duration still need testing. |
| Tesamorelin | Visceral fat stayed reduced during continued treatment and reaccumulated after withdrawal in adults with HIV. | How do benefit and harms balance over longer continued exposure? |
| Semaglutide | SELECT reduced a cardiovascular composite in adults with established cardiovascular disease and overweight or obesity, without diabetes; FLOW reduced a kidney-disease composite in people with type 2 diabetes and chronic kidney disease. | Which outcomes are maintained, in whom and over what further period? |
The differences between these studies defeat a useful league table. The tesamorelin withdrawal experiment gives a direct persistence result. A mouse performance study and a human precursor trial supply different information. Their unanswered questions are more useful than a shared score.
MOTS-c cohort follow-up
The MOTS-c dialysis cohort had a median 26.5-month follow-up. That is a meaningful interval in a population with serious kidney disease, but it tracked the association between naturally occurring MOTS-c and a combined mortality/cardiovascular outcome. It tested no administered MOTS-c.
Elapsed time can lend borrowed authority to a treatment claim. Duration improves our view of the observation actually made. It cannot turn a blood-level cohort into a treatment experiment.
Likewise, the 2025 NAD+ review found limited human efficacy and sparse tissue-specific evidence despite repeated blood increases in precursor trials. More time would help answer some questions; choosing the right clinical outcome would help answer others.
The exposure that accompanies a benefit
Continuing treatment means continuing exposure. The semaglutide safety review found gastrointestinal adverse effects and increased biliary disease, while the tesamorelin liver-safety review judged clinically apparent liver injury unlikely. Those statements concern different drugs and different possible harms.
For an intervention intended to matter over years, I expect the record of harm to grow with the record of benefit. A short reassuring comparison is valuable. So is knowing exactly when its observation ended. The existing studies here establish no general life-extension effect in healthy people.