A Study To Assess the Safety and Efficacy of JZP385 in the Treatment of Adults With Moderate to Severe Essential Tremor (ET)

Change From Baseline to Week 12 on the TETRAS Composite Outcome Score as Summarized by Each Dose of JZP385 and Placebo

Timeframe: Change from baseline to week 12

The TETRAS composite outcome score is the sum of modified items 1 - 11 of the TETRAS-ADL subscale and modified items 6 - 7 of the TETRAS-PS. The TETRAS-ADL subscale is a patient-rated scale administered by a trained interviewer that assesses the impact of tremor on day-to-day functioning, such as eating, drinking, dressing, and other fine motor skills. The TETRAS-PS is a clinical rating scale that quantifies tremor in the head, face voice, limbs and trunk. Items 6 (drawing an Archimedes spiral using left and right hands) and 7 (handwriting) of the TETRAS-PS evaluate the impact of upper limb tremor on performance. Each item from the modified subscales ranges from 0 - 3, with 0 representing normal or slightly abnormal and 3 representing severely abnormal. The sum of the 14 items provides the TETRAS composite outcome score, which ranges from 0 - 42, with higher scores representing more severe ET.

Percentage of Participants Who Improved (≥ 1-Point Improvement) From Baseline to Week 12 on the Clinical Global Impression- Severity Scale (CGI-S)

Timeframe: Change from baseline to week 12

The CGI-S is a 5-point Likert-type rating scale that a qualified medical personnel (ie, a clinician)will use to rate the severity of the participants' ability to function due to their ET. The responses to this scale range from 1 (no limitations) to 5 (severe).

Proportion of Participants Reported as Much Improved on the Clinical Global Impression of Change (CGI-C) at Week 12

Timeframe: Week 12

The CGI-C is a 5-point Likert-type rating scale that a qualified medical personnel (ie, a clinician) will use to rate the change in severity of the participants' ability to function due to their ET since baseline. The responses to this scale range from 1 (Much improved) to 5 (Much worse).

Proportion of Participants Reported as Much Improved on the Patient Global Impression of Change (PGI-C) at Week 12

Timeframe: Change from baseline to week 12

The PGI-C is a 5-point Likert-type rating scale that participants use to rate the change in severity of their ability to function due to ET since baseline. The responses to this scale range from 1 (Much improved) to 5 (Much worse).

Change From Baseline to Week 12 on the TETRAS-ADL Subscale as Summarized by Each Dose of JZP385 and Placebo

Timeframe: Change from baseline to week 12

The TETRAS-ADL subscale is a patient-rated scale of the impact of tremor on day-to-day functioning administered by a trained interviewer. The TETRAS-ADL subscale directly measures how a patient functions by assessing activities impacted by tremor, such as eating and drinking, dressing and personal hygiene, carrying items and fine motor skills. The TETRAS-ADL has 12 items, and each item is rated on a 0 (normal) to 4 (severe) scale with a total score ranging from 0 to 48. A higher score represents more severe ET.

Change From Baseline to Week 12 on the TETRAS-PS Subscale as Summarized by Each Dose of JZP385 and Placebo

Timeframe: Change from baseline to week 12

The TETRAS-PS is a clinical rating scale performed by a blinded rater that quantifies tremor in the head, face, voice, limbs, and trunk. Each item will be rated on a scale of 0 (normal) to 4 (severe). The sum of the individual scores provides the overall score, ranging from 0 to 64, with higher scores representing more severe ET.

Change From Baseline to Week 12 on the Upper Limb Score (Item 4) of the TETRAS-PS as Summarized by Each Dose of JZP385 and Placebo

Timeframe: Change from baseline to week 12

Item 4 of the TETRAS-PS measures upper limb tremor, and includes 3 maneuvers for each arm that assess postural and kinetic tremor. Each item is rated on a scale of 0 (normal) to 4 (severe) in 0.5-point increments. The total score is the sum of each of the 6 items and ranges from 0 to 24, with higher scores representing more severe ET. The TETRAS-PS is performed by a blinded rater.

Change From Baseline to Week 12 on the TETRAS Total Score, as Summarized by Each Dose of JZP385 and Placebo.

Timeframe: Change from baseline to week 12

The TETRAS total score is the sum of the scores of the full TETRAS-ADL and TETRAS-PS subscales. Each item is rated on a 0 (normal) to 4 (severe) scale, and total scores range from 0 to 112, with higher scores representing more severe ET. The TETRAS-PS is performed by a blinded rater.

Change From Baseline to Week 12 on the Quality of Life in Essential Tremor Questionnaire (QUEST) as Summarized by Each Dose of JZP385 and Placebo

Timeframe: Change from baseline to week 12

The Quality of Life in Essential Tremor Questionnaire (QUEST) was developed to specifically assess the impact of ET on health-related quality of life. The QUEST is a 30-item questionnaire comprising 5 subscales (physical, psychosocial, communication, hobbies/leisure, and work/finance). Each item is rated by frequency on a scale from 0 (never) to 4 (always). Each dimension had been standardized to a range of 0 to 100 with higher scores indicating greater dissatisfaction or disability due to ET.

Change From Baseline to Week 12 on the Essential Tremor Embarrassment Assessment (ETEA) Score A as Summarized by Each Dose of JZP385 and Placebo

Timeframe: Change from baseline to week 12

The Essential Tremor Embarrassment Assessment (ETEA) is a participant-rated questionnaire administered by a health care provider or researcher that contains 14-items assessing embarrassment related to tremor. For Score A, participants provide a simple response (disagree or agree) to each of the 14-items, the sum of which yields an initial score range = 0 to 14. Higher scores indicate greater embarrassment

Change From Baseline to Week 12 on the Essential Tremor Embarrassment Assessment (ETEA) Score B as Summarized by Each Dose of JZP385 and Placebo

Timeframe: Change from baseline to week 12

The Essential Tremor Embarrassment Assessment (ETEA) is a participant-rated questionnaire administered by a health care provider or researcher that contains 14-items assessing embarrassment related to tremor. For Score B, participants provide a more nuanced response to each question on a 0 to 5 point Likert scale ranging from disagree (0) to agree strongly (5). The sum of the nuanced responses yields a second score (range = 0 to 70). Higher scores indicate greater embarrassment