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

Inclusion Criteria:

1. Participant must be 18 to 80 years of age inclusive, at the time of signing theinformed consent.

2. Participants who are diagnosed with ET (including ET plus) according to the MDSConsensus Statement on the Classification of Tremors from the Task Force on Tremorof the International Parkinson's and Movement Disorder Society.

3. Participants have moderate to severe disability associated with tremor as determinedby a score of ≥ 22 on the TETRAS-ADL subscale and a CGI-S rating of at leastmoderate for participants' ability to function.

4. Sex and Contraceptive/Barrier Requirements During the study intervention and for at least 30 days after the last dose of studyintervention male participants must refrain from donating sperm. Non-abstinent malesmust agree to use a male condom in combination with female partner use of a highlyeffective contraceptive method with a failure rate of < 1% per year. All maleparticipants must agree to use a male condom when engaging in any activity thatallows for passage of ejaculate to another person. Female participants must not be pregnant or breastfeeding, are either women ofnon-childbearing potential (WONCBP), or are women of childbearing potential (WOCBP)using a highly effective contraceptive method with a failure rate of < 1% during thestudy intervention period and for at least 30 days after the last dose of studyintervention. Male partners of WOCBP are required to use barrier protection, eg,condoms, from the first dose of study intervention until 30 days after the last doseof study intervention. A WOCBP must have a negative highly sensitive serum pregnancy test at ScreeningVisit 1 and negative urine pregnancy tests (unless serum is required by localregulations) at the Screening Visit 2 (if applicable) and at the Baseline Visit

• If a urine test cannot be confirmed as negative (eg, an ambiguous result), aserum pregnancy test is required. In such cases, the participant must beexcluded from participation if the serum pregnancy result is positive.

5. Prior/Concomitant Antitremor Medications

If currently treated with antitremor medications, potential participants must be on a stable dosage for at least 6 weeks prior to Screening and must not anticipate making any changes to their antitremor medication for the duration of the study. Note: Treatment with some antitremor medications (eg, primidone) is not allowed in accordance with other exclusion criteria.

Exclusion Criteria:

1. Known history or current evidence of other medical or neurological conditions thatmay cause or explain the participant's tremor.

2. Has evidence at Screening of severe cognitive impairment as defined by a MontrealCognitive Assessment (MoCA; score < 20) or has cognitive impairment that in theopinion of the investigator would prevent completion of study procedures (includingthe ability to accurately self-report on study questionnaires) or the ability toprovide informed consent.

3. Current suicidal risk as determined from history, by presence of active suicidalideation as indicated by positive response to item 4 or 5 on the C-SSRS (within thepast 24 months), or any history of suicide attempt; current or past (within 1 year)major depressive episode according to DSM-5 criteria.

4. History (within past 2 years at screening) or presence of a diagnosed substance usedisorder (including alcohol, tobacco, and cannabis) according to DSM-5 criteria,known drug dependence, or seeking treatment for alcohol or substance abuse relateddisorder.

5. Prior magnetic resonance (MR)-guided focused ultrasound thalamotomy, surgicalintervention (eg, deep brain stimulation, ablative thalamotomy, gamma knifethalamotomy), or inability to refrain from using a device for treatment of tremorfor the duration of the treatment period.

6. Botulinum toxin injection for the treatment of upper limb tremor in the 6 monthsbefore screening or planned use at any time during the study.

7. Treatment with any medication that could produce tremor taken within 2 weeks or 5half-lives (whichever is longer) before screening or anticipated use at any timeduring participation in the study.

8. Use of prescription of nonprescription drugs or other products known to be inducersof CYP3A4 that are known to decrease AUC by > 30% (eg, primidone) and which cannotbe discontinued at least 4 weeks before Baseline or planned use at any time duringthe study.

9. Use of prescription or nonprescription drugs, or other products (eg, grapefruit,grapefruit juice, or Seville oranges) known to be strong or moderate inhibitors ofCYP3A4, that cannot be discontinued 2 weeks or 5 half-lives, whichever is longer,before Baseline or planned use at any time during the study.

10. Use of proton pump inhibitors that cannot be discontinued at least 2 weeks beforeBaseline, or planned use at any time during the study. Occasional use of antacids orhistamine-2 receptor antagonists will be permitted, but antacids should be taken atleast 4 hours before or after study intervention; and histamine-2 receptorantagonists should be taken at least 4 hours after and at least 12 hours beforestudy intervention.

11. Inability to refrain from use of medication/substance(s) that might produce tremoror interfere with the evaluation of tremor on study visit days prior to dischargesuch as, but not limited to, stimulant decongestants, beta-agonist bronchodilators,and alcohol.

12. Regular use of more than 3 units of alcohol per day.

13. Regular consumption of caffeine > 400 mg/day or > 4 cups of coffee per day