A Trial to Evaluate the Efficacy, Safety, and Tolerability of Centanafadine Sustained-release Tablets in Adults With Attention-deficit/Hyperactivity Disorder

Screening & Washout Period: up to 28 days Investigational Treatment Period: 49 days Follow-up
Period : 7 days or 10 days

Inclusion Criteria:

- Subjects must meet the Diagnostic and Statistical Manual of Mental Disorders Fifth
Edition (DSM-5) criteria for ADHD (including predominantly inattentive presentation,
hyperactive presentation, or combined presentation) as confirmed by the Adult ADHD
Clinical Diagnostic Scale (ACDS) Version 1.2. To confirm that ADHD is the primary
diagnosis, the Mini International Neuropsychiatric Interview (MINI) will be used to
identify and exclude other psychiatric conditions which would preclude enrollment.

- Subjects who were not receiving any pharmacological treatment for ADHD must have an
Adult ADHD Investigator Symptom Rating Scale (AISRS) score of ≥ 28 at screening and
baseline. Subjects who were receiving pharmacological treatment for ADHD at screening
must have a minimum AISRS score of ≥ 22 at screening, and a score of ≥ 28 at baseline.

- All subjects must be willing to discontinue all prohibited psychotropic medications
starting from the time of signing the informed consent through the 7-day follow-up
period. Subjects that do not rollover into Trial 405-201-00015 must be willing to
discontinue all prohibited psychotropic medications starting from the time of signing
the informed consent until after the follow-up telephone call 10 days after the last
dose of IMP.

- Subjects must have a Clinical Global Impression-Severity of Illness Scale (CGI-S)
score of ≥ 4 (≥ moderate impairment) at baseline.

Exclusion Criteria:

- Subject has a DSM-5 Diagnosis of Other Specified or Unspecified Attention
Deficit/Hyperactivity Disorder.

- Subject has a current comorbid psychiatric disorder that either could be expected to
require treatment with medications prohibited in this trial, or to confound efficacy
or safety assessments. Examples include, but are not limited to, psychotic disorder,
bipolar disorder, generalized anxiety disorder, obsessive-compulsive disorder, panic
disorder, a current major depressive episode, or posttraumatic stress disorder, as
established by the MINI.

- In the opinion of the investigator, subject has not derived significant therapeutic
benefit from 2 or more ADHD therapies of 2 different classes (eg, amphetamine and
methylphenidate) given with an acceptable dose and duration of adulthood (aged 18 or
older). NOTE: If subject has not derived significant therapeutic benefit due to an
inability to tolerate side effects, eligibility can be discussed on case-by-case basis
with the medical monitor.

- Subjects that have a positive alcohol test (via breathalyzer or blood), a positive
drug screen for cocaine, or other illicit drugs (excluding marijuana). Subjects with a
positive drug screen for confirmed prescription or over-the-counter (OTC) use of ADHD
medications at screening will be required to undergo a washout period. NOTE: Subjects
that test positive for marijuana may be permitted to be enrolled if they have no
evidence of a substance use disorder, and if they agree to refrain from use for the
duration of the trial. Allowance for subjects testing positive for marijuana at
screening require explicit approval from the medical monitor.

- In the opinion of the investigator, the subject is unable to adhere to the treatment
regimen or other requirements outlined in the protocol.