A Study of JNJ-99245354 (ITI-1284) as an Adjunctive Treatment in Participants With Generalized Anxiety Disorder (GAD) Who Have an Inadequate Response to GAD Treatment

• JNJ-99245354 (Drug), also known as ITI-1284: JNJ-99245354 will be administered sublingually.
• Placebo (Drug): Placebo will be administered sublingually.

Primary outcomes

• Change from Baseline to End of Week 6 in Hamilton Anxiety Rating (HAM-A) Scale Total Score [Baseline, Week 6]: The HAM-A Scale is a clinician-rated scale measuring both psychic anxiety (mental agitation and psychological distress) and somatic anxiety (physical complaints related to anxiety). Each item is rated on a 5-point scale ranging from 0=not present to 4=very severe, disabling symptoms. The HAM-A total score ranges from 0 to 56 where higher score indicates greater severity in anxiety.

Secondary outcomes

• Change from Baseline to the End of Week 6 in Clinical Global Impression-Severity (CGI-S) Anxiety Score [Baseline, Week 6]: The CGI-S scale is a standardized assessment tool that the clinician can use to rate the overall severity of illness. The CGI-S asks the clinician: "Considering your total clinical experience with this particular population, how mentally ill is the participant at this time? CGI-S is rated on the following seven-point scale: 1=normal, not at all ill; 2=borderline ill; 3=mildly ill; 4=moderately ill; 5=markedly ill; 6=severely ill; 7=among the most extremely ill participants. Here, higher score indicates higher symptom severity.
• Change from Baseline to the End of Week 1 in HAM-A Total Score [Baseline, Week 1]: The HAM-A Scale is a clinician-rated scale measuring both psychic anxiety (mental agitation and psychological distress) and somatic anxiety (physical complaints related to anxiety). Each item is rated on a 5-point scale ranging from 0=not present to 4=very severe, disabling symptoms. The HAM-A total score ranges from 0 to 56 where higher score indicates greater severity in anxiety.

Sex: All, ages: 18 Years to any

Inclusion criteria:

* Medically stable on the basis of physical examination, medical history, vital signs, and 12-lead electrocardiogram (ECG) performed at screening and at baseline
* Medically stable on the basis of clinical laboratory tests performed at screening
* History of inadequate response to at least 1 generalized anxiety disorder (GAD)-approved treatment taken at an adequate dose and duration as specified in the protocol for the treatment of ongoing GAD symptoms
* Is currently an outpatient and is anticipated to maintain outpatient status for the duration of the double blind (DB) treatment period of the trial
* Body mass index (BMI) within the range 19-40 kilogram per meter squared (kg/m\^2) (inclusive)

Exclusion criteria:

* Within the participant's lifetime, has one of the following confirmed diagnostic and statistical manual of mental disorders (5th edition) (DSM-5) text revision (TR) psychiatric diagnoses: a. schizophrenia, schizoaffective disorder, schizophreniform disorder or other psychotic disorder; b. bipolar disorder
* Within 6 months of screening, has a confirmed DSM-5-TR psychiatric diagnosis other than GAD, including: a. other anxiety disorders (except simple phobias and social anxiety disorder); b. moderate or severe alcohol or substance use disorders (excluding nicotine); d. moderate or severe major depressive disorder; e. any other psychiatric condition (except for mild major depressive disorder \[MDD\]) that has been the main focus of treatment
* Montgomery-asberg depression rating scale (MADRS) total score greater than (>)18 at screening or baseline
* Lifetime history of inadequate response to >3 of the approved treatments for GAD at an adequate dose and for an adequate duration
* The participant is taking more than 1 anti depressive therapy (ADT) or is taking ADT + buspirone at screening, regardless of indication, and is unable or unwilling to discontinue additional ADT (or buspirone) prior to baseline

• Intra-Cellular Therapies, Inc. Clinical Trial, Study director, Intra-Cellular Therapies, Inc.