NNZ-2591 dosage and evidence
Written by Aaron CuhaReviewed Sep 2026
The short answer
NNZ-2591 is a pill that copies a natural breakdown product of IGF-1, from the makers of trofinetide (Daybue). Since February 2026 it has been in the first ever final-stage study for Phelan-McDermid syndrome.
Evidence grade for NNZ-2591: Limited. The rule: people have taken it in a published study, but fewer than 100 of them. The sum on this page: 1 completed trial, none stating how many people. A grade counts how much has been done to people, not whether it works.
- People given it
- 0
- Human studies
- 1
- Found nothing
- 0
Dose
No human dose established
Amounts that were given in studies sit in Human evidence on this page. None of them is a personal dose.
1 completed trial, 0 people given it
1 effects reported, 1 unwanted, by people using it, not a trial
In plain English
In plain English, from Aaron
This is how I would explain it to a friend. The evidence, with the numbers, is further down the page.
NNZ-2591 is a pill from Neuren, the maker of trofinetide (Daybue). It copies a natural breakdown product of IGF-1. It is being tested in rare genetic conditions that affect how children develop. It is not approved.
What people take it for
- Treating Phelan-McDermid syndrome.
- Treating Angelman and Pitt Hopkins syndromes.
What studies in people showed
The first ever final-stage study in Phelan-McDermid syndrome is giving doses. It has not reported. Mid-stage studies in Angelman and Pitt Hopkins syndromes are published, but their results are not on this page. A long-term safety study is also running.
What people report
Reports, not study results
The good
- We have not collected user reports on this one yet.
The bad
- No results from the final-stage study have been reported yet.
Where these come from: Everything here is from the study records on this page. There are no user reports.
My bottom line
This is for families with a rare diagnosis, working with a specialist. It is not a brain booster.
An opinion, not a finding. I am a coach, not a doctor.
What it has been measured to do
Nothing indexed yet
The 2 citations on this page do not report a result for any of the 36 goals indexed here. Most of what sits here is something else: a listing of a planned study, a study of how the body handles the drug, a safety report or a government record. None of those tests whether it works.
Show full evidence
What is NNZ-2591?
NNZ-2591 is a pill that copies a natural breakdown product of IGF-1, from the makers of trofinetide (Daybue). Since February 2026 it has been in the first ever final-stage study for Phelan-McDermid syndrome.
NNZ-2591 is a lab-made copy of cyclic glycine-proline, a natural breakdown product of IGF-1. It is a sister drug to trofinetide, which Neuren took to approval for Rett syndrome. It has several FDA labels that help rare disease drugs along: Fast Track, Orphan and Rare Pediatric. The 13-week final-stage Koala study in Phelan-McDermid syndrome, a rare genetic condition that affects development, is giving doses. Mid-stage studies in Angelman and Pitt Hopkins syndromes are published. It is the closest thing to a successor to davunetide for these childhood brain conditions.
How does NNZ-2591 work?
It brings IGF-1 and nerve cell signals in the brain back toward normal, helping nerve cells connect in these developmental conditions.
The evidence, in charts
Fig. 1a · how many people
2studies in people cited, but none says how many people took part
number of people not stated
We do not draw a total, because none of the studies in people on this page gives one. Read the sources below for what each study measured.
We read the number of people from the source lines on this page. Where a line gives no number, we count nothing for it. We do not guess.
Fig. 1b · evidence mix
All 2 sources here are studies in people.
- Study in people · done in people2100%
Counted from the list of sources on this page. It counts only what we cite, so there may be more studies out there. A review counts once, however many studies it sums up.
Fig. 2 · evidence over time
Every source here was published in 2026.
Too few different years on this page to draw a timeline.
Fig. 3 · legal status at a glance
US
Not approved
UK
Not approved
AU
Not approved
CA
Not approved
Not approved in any of the four countries shown. This is what the law says, not a verdict on the science. See Legal status below for the full text and any notes.
Fig. 4 · how much does what
Nobody has tested different amounts in people
This chart would show how the effect changes as the amount goes up. For this compound, nobody has measured that in people. So we leave it empty. We will not borrow an animal chart and pretend it works the same in people.
Fig. 5 · what the molecule is
- Kind of compound
- Small molecule
- Molecule weight
- 194.2 Da
- Half-life
- Stated in words, not a numbersee the exact wording below
- Chain length
- None on file
No amino acid sequence is on file for NNZ-2591, which is expected: a small molecule is not built from amino acids.
The studies we cite
- Study in people2026Koala: NNZ-2591 Phase 3 in Phelan-McDermid syndrome
This trial is running and has published nothing. It is the first large final-stage trial ever run in Phelan-McDermid syndrome, a rare genetic condition affecting development. Being first is a real milestone for families who have no approved treatment. It is not a result. Dosing is under way and nothing has been reported.
First Phase 3 in the condition.
- Study in people2026NNZ-2591 open-label extension
This study is running and has published nothing. Everybody in it gets the drug and everybody knows it, because its job is to watch for harm over a longer stretch rather than to test whether the drug works. A study built this way cannot show benefit. No results have been posted.
Long-term safety study.
Common questions
Has NNZ-2591 been tested in people?
Yes. 0 people given it across 1 completed trial cited here, 0 of which found nothing. NNZ-2591 is a pill that copies a natural breakdown product of IGF-1, from the makers of trofinetide (Daybue). Since February 2026 it has been in the first ever final-stage study for Phelan-McDermid syndrome.
What is the NNZ-2591 dosage?
No human dose established. Amounts that were given in studies sit in Human evidence on this page. None of them is a personal dose. 1 completed trial, 0 people given it
Is NNZ-2591 FDA-approved?
Investigational; in final-stage studies. The FDA gave it Fast Track and Orphan (rare disease) status
Is NNZ-2591 related to davunetide?
Only loosely. Both are short molecules that act in the brain and come from natural brain-protecting peptides. Davunetide comes from ADNP. NNZ-2591 comes from a breakdown product of IGF-1.