July 24, 2026 - The FDA has approved Simtriyo® (centanafadine) developed by Otsuka Pharmaceutical. As a first-in-class and novel norepinephrine-dopamine-serotonin reuptake inhibitor (NDSRI), Simtriyo® has demonstrated significant efficacy and a favorable safety profile in recent large-scale trials. Therefore, the drug has been recently approved by the FDA as a promising new treatment for Attention-Deficit/Hyperactivity Disorder (ADHD) in children ages 6 years and older who at least weigh 20 kilograms.
The NDSRI Mechanism
In a healthy brain, neurotransmitters (dopamine, norepinephrine, and serotonin) are released into the synaptic cleft to transmit signals between neurons. They are subsequently removed from the cleft via specialized proteins called transporters (DAT, NET, and SERT). Centanafadine binds to these transporters, inhibiting the reuptake process. This results in increased extracellular concentrations of all three monoamines, enhancing neurotransmission in the pathways responsible for attention, impulse control, and mood regulation.
Traditional ADHD treatments often focus on dopamine and/or norepinephrine, thereby falling into two categories:
- Stimulants (e.g., Amphetamines): Primarily target dopamine and norepinephrine. They are highly effective but carry high abuse potential and cardiovascular risks.
- Non-stimulants (e.g., Atomoxetine): Primarily target norepinephrine. They are safer but often have a slower onset of action and may be less effective for core ADHD symptoms.
Simtriyo’s® NDSRI activity is unique because it targets three key neurotransmitter systems to inhibit the reuptake of dopamine, norepinephrine, and serotonin simultaneously. Additionally incorporating serotonin (5-HT) reuptake inhibition into the treatment of ADHD results in the drug’s “triple action" mechanism. This provides a steady, long-term relief and address not only the core ADHD symptoms like inattentiveness, hyperactivity and impulsivity, but also for common ADHD comorbidities, such as anxiety and depression, which are often addressed by separate medications in standard practice.
Furthermore, centanafadine is unique in how it interacts with the Dopamine Transporter (DAT). While other triple reuptake inhibitors (TRIs) stabilize the transporter in an "outward-facing" conformation (accessible from the extracellular side), the drug stabilizes the DAT in an "inward-facing" conformation. This means it binds deeply within the central cavity, effectively "trapping" the transporter in a state that prevents the movement of dopamine, providing a distinct profile of inhibition.
Simtriyo Structure
The chemical structure consists of a bicyclic core containing a fused cyclopropane and pyrrolidine ring (Figure 1). The aromatic napthalene ring system attaches to the core's 2-substituted position. The molecule is highly stereospecific as observed by its bridgehead carbons absolute configuration of 1R, 5S steroisomerism.
Figure 1. Structure of Simtriyo® (centanafadine)
Clinical Development and Trial Phases
The clinical progression of centanafadine has demonstrated consistent efficacy and long-term safety:
- Phase 2 Trials: These early studies established the drug's efficacy. Results showed that twice-daily centanafadine sustained-release (SR) significantly reduced core ADHD symptoms (measured by the ADHD Rating Scale IV) compared to placebo, with significant improvement observed as early as Week 1.
- Phase 3 Pivotal Trials: Two randomized, double-blind, placebo-controlled trials (6 weeks in duration) were conducted to confirm efficacy. Participants receiving 200 mg or 400 mg total daily doses (TDD) showed significantly improved scores on the Adult ADHD Investigator Symptom Rating Scale (AISRS) compared to the placebo group.
- Long-term Study (52-week): A major study was conducted to assess long-term safety and tolerability in adults.
- Efficacy: Patients showed a 49.1% to 56.7% improvement in AISRS total scores from baseline over one year. Clinically meaningful improvements were also noted in the Clinical Global Impression–Severity (CGI-S) scale.
- Stability: The drug demonstrated sustained effectiveness throughout the 52-week period without significant loss of efficacy.
Safety
One of the primary hurdles in ADHD medication is managing potential side effects. Centanafadine has been generally well-tolerated. In long-term studies, the most common Treatment-Emergent Adverse Events (TEAEs) included:
- Insomnia (8.0%)
- Nausea (7.7%)
- Diarrhea (7.0%)
- Headache (7.0%)
Clinical data indicates that while side effects like headache and decreased appetite were reported, they were generally mild to moderate. Furthermore, studies showed that Simtriyo® possesses a low potential for abuse, since there were no reports of euphoric mood that suggests a lower potential for misuse or abuse compared to traditional stimulants. The Study Medication Withdrawal Questionnaire (SMWQ) also indicated no significant drug withdrawal symptoms after discontinuation.
Recommended Dosage and Administration
Simtriyo® is administered as a sustained-release (SR) tablet.
Clinical trials have reported dosage following a schedule to minimize side effects:
- Initial Dose: 200 mg total daily dose (administered as 100 mg twice daily) for the first 7 days.
- Target Dose: 400 mg total daily dose (administered as 200 mg twice daily).
- Note: If tolerability issues occur, it has been reported in literature that investigators may temporarily reduce the dose back to 200 mg TDD.
Alternatives and Competition
| Feature | Stimulants (e.g., Vyvanse, Concerta) | Non-Stimulants (e.g., Strattera, Qelbree) | Simtriyo® (Centanafadine) |
|---|---|---|---|
| Mechanism | Dopamine/Norepinephrine (DA/NE) | Primarily Norepinephrine (NE) | Triple (DA/NE/5-HT) |
| Control Status | Schedule II (High abuse potential) | Non-scheduled | Pending DEA review |
| Onset of Action | Rapid | Slow (weeks) | Rapid (as early as Week 1) |
| Main Drawbacks | High misuse risk; cardiovascular concerns. | May be less effective; risk of suicidal ideation. | New drug; long-term data establishing. |
Outlook
Simtriyo® could become a vital tool for healthcare providers, especially for patients who have not responded well to standard treatments or who require a safer, non-stimulant profile. Ongoing studies continue to investigate its long-term safety and its potential to treat co-morbid conditions like anxiety and depression, which often appear alongside ADHD.
References
- Raoufinia, A.; et al. At-Home Self-Collection of Pharmacokinetic Data. Clinical Pharmacology in Drug Development 2025, 14 (1), 11-17.
- Tu, G.; et al. Understanding the Polypharmacological Profiles of Triple Reuptake Inhibitors by Molecular Simulation. ACS Chemical Neuroscience 2021, 12 (11), 2013-2026.
- Chang, D.; et al. Efficacy, Safety, and Tolerability of Centanafadine Sustained-Release Tablets in Adults With ADHD. Journal of Clinical Psychopharmacology 2022, 42 (5), 429-439.
- Li, Y.; et al. Structural basis for pharmacotherapeutic action of triple reuptake inhibitors. Nature Communications 2025, 17 (1), 61.
- Simtriyo. Prescribing information. Otsuka Pharmaceutical, 2026.
- Otsuka Pharmaceutical. Otsuka Receives FDA Approval for First-in-Class SIMTRIYO® (centanafadine). 2026.