Which fragile x syndrome drugs are in Phase 3?

Phase 3 (or later) programs for fragile x syndrome include Zatolmilast.

What are the next fragile x syndrome trial readouts?

Upcoming catalysts include Zatolmilast (2H 2026).

How many clinical trials are recruiting for fragile x syndrome?

10 drug-interventional fragile x syndrome trials are currently recruiting participants, out of 73 registered interventional trials.

Neurodevelopmental Disorders

Fragile X syndrome drug pipeline

ICD-11 LD55
MeSH D005600

2 compounds from 2 companies are in active clinical development for fragile x syndrome, including 1 at Phase 3 or beyond.

2Compounds

2Companies

1Phase 3+

1Upcoming readout

10Trials recruiting

Phase 31

ZatolmilastShionogi & Co., Ltd.PDE4D NAM

Discontinued1

MavoglurantNovartis Pharma AGmGlu5 NAM

Mechanisms: Small molecule (2)

Pipeline data compiled September 2026 · every fact sourced.

Upcoming readouts & recent results

2H 2026AnticipatedZatolmilastFull resultsNCT05367960
Program-decision update on zatolmilast in fragile X syndrome: Shionogi plans to analyze the EXPERIENCE-302 open-label extension alongside exploratory analyses of EXPERIENCE-301/-204, engage the FDA, and update the FXS community in the second half of 2026 — effectively the program's go/no-go catalyst. ↗
2026-05-13ReportedZatolmilastTopline datamissedNCT05358886
EXPERIENCE-301 (adult) missed its primary endpoint: zatolmilast did not improve the NIH Toolbox Crystallized Cognition Composite vs placebo at Week 13 in adult males with fragile X syndrome, though significant caregiver-rated FXS-NRS language/communication and daily-function differences were observed ('suggestive of an efficacy signal', not conclusive). ↗
2026-05-13ReportedZatolmilastTopline datamissedNCT05163808
EXPERIENCE-204 (adolescent) missed its primary endpoints (FXS-NRS language/communication and daily function) and its key secondary (CGI-I of Language) in male adolescents with fragile X syndrome; generally well tolerated, no new safety concerns. ↗

See the full catalyst calendar →

Compounds in development (2)

Compound	Company	Phase	Status	Mechanism
ZatolmilastFDA Orphan Drug Designation (Fragile X Syndrome; 2018)FDA Rare Pediatric Disease Designation (Fragile X Syndrome; Granted 2023-09-27)	Shionogi & Co., Ltd.	Phase 3	Active	PDE4D NAM
Mavoglurant	Novartis Pharma AG	Discontinued	Discontinued	mGlu5 NAM

Trials recruiting now (10)

10 drug-interventional fragile x syndrome trials recruiting now, of 73 registered interventional trials. Browse all on ClinicalTrials.gov →

Phase 4Metformin in Children With Fragile X Syndrome
Metformin, Placebo
Children's Hospital of Fudan Universityn=20China · 1 siteStarted Dec 2021NCT05120505
Phase 4The Psychiatric and Cognitive Phenotypes in Velocardiofacial Syndrome
methylphenidate, fluoxetin, risperidone
The Chaim Sheba Medical Centern=400Israel · 1 siteStarted May 2001NCT00768820
Phase 2/3A Study to Investigate the Effects and Safety of SPG601 for the Treatment of Fragile X Syndrome in Male Participants
SPG601, Placebo
Spinogenixn=248Started Mar 2026NCT07439510
Phase 2Safety, Tolerability, and Preliminary Effectiveness of CTH120 in Fragile X Syndrome
CTH120
Connecta Therapeutics, S.L.n=30Spain · 2 sitesStarted May 2026NCT07654114
Phase 2Inhibition of Aggressive Behavior in Participants With Fragile X Syndrome
SRX246, Placebo
Azevan Pharmaceuticalsn=80United States · 3 sitesStarted Mar 2026NCT07328529
Phase 2Study of MRM-3379 in Male Participants With Fragile X Syndrome (BLOOM)
Low dose of MRM-3379, Middle Dose of MRM-3379, High dose of MRM-3379, Placebo, Low dose of MRM-3379 Open-Label
Mirum Pharmaceuticals, Inc.n=60United States · 15 sitesStarted Nov 2025NCT07209462
Phase 2Effect of CBD on the Brain
CBD Oral Solution (eCBD system Target), Placebo
Université de Sherbrooken=50Started May 2025NCT06261450
Phase 2Effect of CANnabidiol on Anxiety and GABAergic Function in Individuals with Fragile-X Syndrome
CBD Oral Solution, Placebo
Université de Sherbrooken=40Started May 2025NCT06261502
Phase 2Sertraline vs. Placebo in the Treatment of Anxiety in Children and AdoLescents With NeurodevelopMental Disorders
Sertraline
Holland Bloorview Kids Rehabilitation Hospitaln=130Canada · 8 sitesStarted Sep 2024NCT06081348
Phase 1Sensitivity of the NIH Toolbox to Stimulant Treatment in Intellectual Disabilities
Methylphenidate Oral Solution
University of California, Davisn=68United States · 3 sitesStarted Feb 2023NCT05301361

Frequently asked

How many drugs are in development for fragile x syndrome?: 2 compounds from 2 companies are in active clinical development for fragile x syndrome, including 1 at Phase 3 or beyond.
Which fragile x syndrome drugs are in Phase 3?: Phase 3 (or later) programs for fragile x syndrome include Zatolmilast.
What are the next fragile x syndrome trial readouts?: Upcoming catalysts include Zatolmilast (2H 2026).
How many clinical trials are recruiting for fragile x syndrome?: 10 drug-interventional fragile x syndrome trials are currently recruiting participants, out of 73 registered interventional trials.