Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that destroys motor neurons, leaving patients without effective disease-modifying treatments. Researchers have investigated whether tauroursodeoxycholic acid (TUDCA) — a hydrophilic bile acid known to reduce endoplasmic reticulum stress and block mitochondrial apoptosis pathways — might slow this destruction. The rationale is biologically plausible: motor neurons in ALS show signs of proteotoxic stress and mitochondrial dysfunction, both of which TUDCA targets in preclinical models.
Over the past decade, several clinical trials have put this hypothesis to the test, both with TUDCA alone and with a fixed-dose combination pairing it with sodium phenylbutyrate (NaPB). The journey has moved from early cautious optimism to a sobering reassessment. This article summarizes what the trials found, what their limitations were, and what the current evidence honestly supports — without overstating a field that remains unsettled.
Key Takeaways
- TUDCA (taurursodiol) targets ER stress and mitochondrial apoptosis, both implicated in ALS motor neuron death — making the biological rationale reasonable but not sufficient on its own.
- The CENTAUR Phase 2 trial found that a combination of NaPB and taurursodiol slowed functional decline in ALS, with follow-up data suggesting a survival signal [PMID 32877582, PMID 33063909].
- A 2024 reassessment characterizes the NaPB-taurursodiol story as ‘hope turned to disappointment,’ indicating that larger or confirmatory data did not sustain the Phase 2 optimism [7].
- The dedicated TUDCA-ALS trial tested TUDCA alone as add-on therapy with a rigorous pre-registered design [PMID 36237618, PMID 38053196]; its results represent the most direct evidence on TUDCA’s independent contribution.
- Current evidence does not establish TUDCA as a proven ALS treatment; it remains an active research area with unresolved questions about efficacy at meaningful scale.
Why TUDCA? The Biological Rationale in ALS
In ALS, motor neuron death involves at least two well-documented stress pathways: misfolded protein accumulation in the endoplasmic reticulum (ER stress) and dysfunction of the mitochondrial outer membrane that triggers intrinsic apoptosis. TUDCA addresses both. As a taurine-conjugated, water-soluble bile acid, it acts as a chemical chaperone that stabilizes misfolded proteins in the ER, reducing the unfolded protein response. It also inserts into the mitochondrial membrane and inhibits cytochrome c release, blocking the cascade that leads to programmed cell death.
This dual-pathway action made TUDCA an attractive candidate for ALS — a disease where no single mechanism explains neurodegeneration but where ER stress and mitochondrial failure are consistently implicated. The challenge, as in nearly all neurodegeneration research, is translating promising cell and animal data into meaningful benefit for human patients.
The First Human Trial: Early Evidence From 2016
The first published clinical investigation of TUDCA specifically in ALS patients came from a 2016 study [1] published in the European Journal of Neurology. This trial tested TUDCA as an add-on treatment in ALS patients and represented an early signal that the compound might be safe and potentially beneficial in this population.
While the scale and design of this early trial were limited — a common constraint at the exploratory stage of drug development — it provided a foundation for proceeding to larger, more rigorous investigations. Critically, it did not establish efficacy on its own; it raised a testable hypothesis that warranted further study. Readers should not interpret a single early-phase trial, however promising its direction, as confirmation of benefit.
The CENTAUR Trial: A Combination Approach and Phase 2 Optimism
The most prominent clinical evidence involving taurursodiol (TUDCA) in ALS came from the CENTAUR trial, published in The New England Journal of Medicine in 2020 [2]. This Phase 2 randomized controlled trial tested AMX0035 — a fixed-dose combination of sodium phenylbutyrate (NaPB) and taurursodiol — against placebo in ALS patients. The rationale for combining NaPB with TUDCA was to simultaneously target ER stress (NaPB) and mitochondrial apoptosis (taurursodiol) in a complementary fashion.
The trial reported that participants receiving AMX0035 experienced a statistically significant slowing of functional decline compared to placebo, as measured by the ALS Functional Rating Scale-Revised (ALSFRS-R). This was a meaningful result in a disease where slowing decline by any measurable amount is clinically significant. The combination was also reported to be generally tolerable, which matters for a population already coping with a physically demanding illness.
Long-term follow-up data from CENTAUR participants, published in Muscle & Nerve in 2021 [3], suggested that survival favored the treatment arm, adding to the Phase 2 case for the combination. These results attracted considerable attention and generated genuine hope in the ALS community.
The TUDCA-ALS Trial: Testing TUDCA Alone at Larger Scale
Separate from the CENTAUR combination work, Italian researchers designed a dedicated trial to test TUDCA as a standalone add-on therapy in ALS. The TUDCA-ALS trial protocol was published in Frontiers in Neurology in 2022 [4], laying out a rigorous Phase 3 randomized, double-blind design with TUDCA at 2 g per day added to standard care (riluzole). This was a larger, more definitive test of TUDCA’s independent contribution — not bundled with NaPB.
The statistical analysis plan for the TUDCA-ALS trial was published in Trials in 2023 [6], detailing the primary outcome (ALSFRS-R slope), secondary survival endpoints, and pre-specified subgroup analyses. Publishing a statistical analysis plan before unblinding is a mark of methodological rigor — it prevents post-hoc outcome selection and makes the eventual results more credible regardless of their direction. This transparency was a strength of the trial design.
Hope Turned to Disappointment: The Evidence Reassessed
A 2024 review published in Clinical Drug Investigation [7] framed the arc of sodium phenylbutyrate and taurursodiol in ALS research as ‘a story of hope turned to disappointment.’ This framing signals that subsequent data — from larger trials or confirmatory studies — did not sustain the optimism generated by CENTAUR’s Phase 2 results.
This is a critical piece of context for anyone evaluating TUDCA’s role in ALS. Phase 2 trials are designed to detect signals and determine whether a treatment is worth testing at scale; they are not definitive evidence of efficacy. When Phase 2 signals fail to replicate in Phase 3 or in independent populations, the scientific consensus updates accordingly. The 2024 reassessment [7] reflects that updating process and underscores why preliminary results — even those published in high-profile journals — must be interpreted with appropriate caution.
An expert review in Expert Review of Neurotherapeutics in 2023 [5] similarly provided a critical evaluation of the NaPB and taurursodiol combination, weighing the evidence from CENTAUR against its limitations and the broader context of ALS drug development, where many promising Phase 2 candidates have failed to replicate.
What This Means for Understanding TUDCA's Role
Taken together, the clinical record on TUDCA in ALS shows a compound with a plausible mechanism, early encouraging signals in small trials [1], a notable Phase 2 result in combination with NaPB [2], and long-term survival data pointing in a positive direction [3] — followed by a subsequent reassessment suggesting that the promise was not fully borne out at larger scale [7].
The TUDCA-ALS trial [PMID 36237618, PMID 38053196] represents the most rigorous test of TUDCA as an independent agent in ALS. Whatever its outcome, it provides higher-quality evidence than the earlier combination trial could offer about TUDCA’s standalone contribution. ALS drug development has a long history of Phase 2 signals that did not survive Phase 3 scrutiny, and the current evidence base for TUDCA sits within that difficult reality.
None of this means TUDCA is without interest as a research target. It means the current evidence does not establish it as an effective treatment for ALS, and anyone interpreting the Phase 2 data as proof of efficacy would be going beyond what the trial design supports.
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A Note on the Evidence
The clinical evidence for TUDCA in ALS is still evolving, and initial positive signals from Phase 2 research have not been definitively confirmed at larger scale [PMID 38909349]; no one should interpret this article as support for self-treating ALS with TUDCA supplements, which is not a substitute for neurological care, approved medications, or enrollment in an appropriately supervised clinical trial.
Frequently Asked Questions
What is taurursodiol and is it the same as TUDCA?
Yes. Taurursodiol is the pharmaceutical name for tauroursodeoxycholic acid, the same compound sold as TUDCA in supplement form. In clinical trial literature, especially the CENTAUR research [2], the term taurursodiol is used interchangeably with TUDCA.
What did the CENTAUR trial actually find?
CENTAUR was a Phase 2 randomized controlled trial testing a combination of sodium phenylbutyrate and taurursodiol (AMX0035) in ALS patients. It reported a statistically significant slowing of functional decline on the ALSFRS-R scale compared to placebo [2]. Long-term follow-up also suggested a survival benefit in the treatment group [3]. These were Phase 2 results, not Phase 3 confirmation.
Why is the evidence now described as disappointing if the CENTAUR trial was positive?
Phase 2 trials are designed to detect signals, not confirm efficacy. A 2024 review [7] describes the trajectory of NaPB-taurursodiol in ALS as ‘hope turned to disappointment,’ indicating that subsequent data did not sustain the Phase 2 findings to the degree needed for confident clinical use. This pattern — promising Phase 2, inconclusive Phase 3 — is common in ALS drug development.
Is there a trial testing TUDCA alone, not in combination with NaPB?
Yes. The TUDCA-ALS trial, a Phase 3 randomized, double-blind study, was designed to test TUDCA at 2 g per day as an add-on to standard ALS care independently of sodium phenylbutyrate. Its protocol was published in 2022 [4] and its pre-registered statistical analysis plan in 2023 [6]. This trial represents the most direct test of TUDCA’s standalone effect in ALS.
Is TUDCA safe to take for ALS outside of a clinical trial?
Safety data from the clinical trials reviewed here suggest TUDCA is generally tolerable, but this does not mean self-supplementation is appropriate for ALS patients. TUDCA is contraindicated in bile duct obstruction and requires medical supervision in patients with gallbladder disease or hepatic impairment. ALS patients are typically on complex medication regimens, and potential interactions with riluzole or other agents have not been fully characterized. This question should be directed to the treating neurologist.
Were there any earlier human trials of TUDCA in ALS before CENTAUR?
Yes. A 2016 study published in the European Journal of Neurology [1] investigated TUDCA in ALS patients and provided early clinical data. This was a smaller, exploratory trial that helped justify the subsequent, larger investigations but was not in itself sufficient to establish efficacy.
References
- Elia AE et al. Tauroursodeoxycholic acid in the treatment of patients with amyotrophic lateral sclerosis. European journal of neurology (2016). PMID 25664595
- Paganoni S et al. Trial of Sodium Phenylbutyrate-Taurursodiol for Amyotrophic Lateral Sclerosis. The New England journal of medicine (2020). PMID 32877582
- Paganoni S et al. Long-term survival of participants in the CENTAUR trial of sodium phenylbutyrate-taurursodiol in amyotrophic lateral sclerosis. Muscle & nerve (2021). PMID 33063909
- Albanese A et al. Tauroursodeoxycholic acid in patients with amyotrophic lateral sclerosis: The TUDCA-ALS trial protocol. Frontiers in neurology (2022). PMID 36237618
- Sun Y et al. An evaluation of the combination of sodium phenylbutyrate and taurursodiol for the treatment of amyotrophic lateral sclerosis. Expert review of neurotherapeutics (2023). PMID 36705941
- Lombardo FL et al. A randomized double-blind clinical trial on safety and efficacy of tauroursodeoxycholic acid (TUDCA) as add-on treatment in patients affected by amyotrophic lateral sclerosis (ALS): the statistical analysis plan of TUDCA-ALS trial. Trials (2023). PMID 38053196
- Ketabforoush A et al. Sodium Phenylbutyrate and Tauroursodeoxycholic Acid: A Story of Hope Turned to Disappointment in Amyotrophic Lateral Sclerosis Treatment. Clinical drug investigation (2024). PMID 38909349
These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure, or prevent any disease. Content is for informational purposes only and is not medical advice; consult a qualified healthcare provider before starting any supplement. As an Amazon Associate we earn from qualifying purchases.