Sodium phenylbutyrate
Sodium phenylbutyrate (4-phenylbutyrate), chemical chaperone and HDAC inhibitor
Written by Aaron CuhaReviewed Sep 2026
Also known as: 4-phenylbutyrate, 4-PBA, Buphenyl, Pheburane
A chemical chaperone that relieves endoplasmic reticulum stress, and a weak HDAC inhibitor, so it targeted two ageing mechanisms at once. It did not extend mouse lifespan in either sex.
Overview
This compound was an attractive candidate because it hits two things on the standard list of ageing hallmarks. Loss of proteostasis is one, and 4-phenylbutyrate is a chemical chaperone that helps misfolded proteins fold and relieves endoplasmic reticulum stress. Epigenetic alteration is another, and it is a weak histone deacetylase inhibitor.
It is also an approved drug, for urea cycle disorders, so its dosing and safety in humans were already known. And it has a further human record as part of a combination product for amyotrophic lateral sclerosis, which was later withdrawn from the market after its confirmatory phase 3 failed.
In the Interventions Testing Program's 2024 cohort it did not increase lifespan in either sex.
Mechanism of action
Two established activities. As a chemical chaperone it stabilises protein folding intermediates non-specifically and reduces the unfolded protein response, which is the basis of its use in conditions of protein misfolding. As a weak histone deacetylase inhibitor it increases histone acetylation and alters gene expression. It is also a nitrogen scavenger, conjugating with glutamine to form phenylacetylglutamine that is excreted renally, which is the mechanism behind its urea cycle disorder approval and is unrelated to the ageing rationale.
Human evidence
Approved for a rare metabolic disease, with a separate and instructive history in amyotrophic lateral sclerosis. No ageing endpoints.
- Approved for urea cycle disorders, where it acts as a nitrogen scavenger rather than through proteostasis.
- A combination product containing it received approval for amyotrophic lateral sclerosis on the strength of a small trial, and was withdrawn after the larger confirmatory phase 3 failed to confirm benefit.
- Palatability is a genuine clinical problem, and the dosing burden is high because of the short half-life.
- Sodium load matters at therapeutic doses, which is relevant to anyone with hypertension or heart failure.
- No human study has examined lifespan, healthspan or any ageing endpoint.
What this does not tell you: The urea cycle approval rests on nitrogen scavenging and says nothing about the proteostasis rationale. The ALS story is a caution rather than support: an early positive result did not survive a properly powered confirmatory trial, which is the same pattern this site documents repeatedly. The mouse lifespan null is the only direct test of the ageing hypothesis and it was negative.
Reading the research record
Two independent negatives about the same compound in the same few years is worth noting. Its lifespan test in mice found nothing, and its most prominent human application, in amyotrophic lateral sclerosis, was approved on a small trial and then withdrawn when the confirmatory phase 3 did not hold up.
The proteostasis hypothesis itself is not damaged much by this. 4-phenylbutyrate is a weak and non-specific chaperone, and a null from a blunt tool constrains the tool more than the idea. But it is the only lifespan test the hypothesis has had.
The Interventions Testing Program is run by the National Institute on Aging at three independent sites, The Jackson Laboratory, the University of Michigan and the University of Texas Health Science Center at San Antonio. It uses UM-HET3 mice, a genetically heterogeneous four-way cross, so a result cannot be an artefact of one inbred strain. Compounds are fed in the diet, both sexes are tested, cohorts are large enough to detect roughly a 10 percent lifespan change, and results are analysed by log-rank for median survival and by the Wang-Allison test for maximum lifespan. Its nulls are published alongside its positives. That combination of features does not exist anywhere else in ageing research, which is why a null here means considerably more than a null from a single laboratory.
The evidence, charted
Fig. 1 · evidence composition
0of 1 citation (0%) is in people
Every citation cited here is Animal work; no other study type is cited on this page. This count is of our own citation list and understates any literature larger than the sources we cite.
Fig. 2 · evidence over time
Every citation here was published in 2024.
Too few distinct publication years on this page to plot as a timeline.
Fig. 3 · legal status at a glance
US
Approved
UK
Approved
AU
Approved
CA
Approved
Approved in all four jurisdictions shown. A jurisdiction's classification is a regulatory fact, not a verdict on the science; see Legal status below for the full text and any notes.
Key studies & citations
- Animal2024
Astaxanthin and meclizine extend lifespan in UM-HET3 male mice; fisetin, SG1002, dimethyl fumarate, mycophenolic acid, and 4-phenylbutyrate do not
Interventions Testing Program. 4-phenylbutyrate did not increase lifespan significantly at the dose and method of administration tested, in either sex.
GeroScience
Frequently asked questions
Does relieving endoplasmic reticulum stress extend lifespan?
The one lifespan test using a chemical chaperone found nothing in either sex. The compound is weak and non-specific, so the hypothesis is better described as inadequately tested than refuted. There is no positive mammalian lifespan evidence for it.
What happened with the ALS drug?
A combination product containing 4-phenylbutyrate was approved for amyotrophic lateral sclerosis based on a small trial, and was withdrawn from the market after the larger confirmatory phase 3 failed to confirm the benefit. It is a textbook case of an early positive result not surviving proper testing.
Is it worth taking?
Nothing supports it for ageing. Practically it also has a short half-life requiring frequent dosing, a significant sodium load and notoriously poor palatability.