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

Inclusion criteria

• Participant must be 18 to 80 years of age inclusive, at the time of signing the informed consent.
• Participants who are diagnosed with ET (including ET plus) according to the MDS Consensus Statement on the Classification of Tremors from the Task Force on Tremor of the International Parkinson's and Movement Disorder Society.
• Participants have moderate to severe disability associated with tremor as determined by a score of ≥ 22 on the TETRAS-ADL subscale and a CGI-S rating of at least moderate for participants' ability to function.
• Sex and Contraceptive/Barrier Requirements

During the study intervention and for at least 30 days after the last dose of study intervention male participants must refrain from donating sperm. Non-abstinent males must agree to use a male condom in combination with female partner use of a highly effective contraceptive method with a failure rate of < 1% per year. All male participants must agree to use a male condom when engaging in any activity that allows for passage of ejaculate to another person.

Female participants must not be pregnant or breastfeeding, are either women of non-childbearing potential (WONCBP), or are women of childbearing potential (WOCBP) using a highly effective contraceptive method with a failure rate of < 1% during the study intervention period and for at least 30 days after the last dose of study intervention. 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 dose of study intervention.

A WOCBP must have a negative highly sensitive serum pregnancy test at Screening Visit 1 and negative urine pregnancy tests (unless serum is required by local regulations) 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), a serum pregnancy test is required. In such cases, the participant must be excluded from participation if the serum pregnancy result is positive.
• 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

• Known history or current evidence of other medical or neurological conditions that may cause or explain the participant's tremor.
• Has evidence at Screening of severe cognitive impairment as defined by a Montreal Cognitive Assessment (MoCA; score < 20) or has cognitive impairment that in the opinion of the investigator would prevent completion of study procedures (including the ability to accurately self-report on study questionnaires) or the ability to provide informed consent.
• Current suicidal risk as determined from history, by presence of active suicidal ideation as indicated by positive response to item 4 or 5 on the C-SSRS (within the past 24 months), or any history of suicide attempt; current or past (within 1 year) major depressive episode according to DSM-5 criteria.
• History (within past 2 years at screening) or presence of a diagnosed substance use disorder (including alcohol, tobacco, and cannabis) according to DSM-5 criteria, known drug dependence, or seeking treatment for alcohol or substance abuse related disorder.
• Prior magnetic resonance (MR)-guided focused ultrasound thalamotomy, surgical intervention (eg, deep brain stimulation, ablative thalamotomy, gamma knife thalamotomy), or inability to refrain from using a device for treatment of tremor for the duration of the treatment period.
• Botulinum toxin injection for the treatment of upper limb tremor in the 6 months before screening or planned use at any time during the study.
• Treatment with any medication that could produce tremor taken within 2 weeks or 5 half-lives (whichever is longer) before screening or anticipated use at any time during participation in the study.
• Use of prescription of nonprescription drugs or other products known to be inducers of CYP3A4 that are known to decrease AUC by > 30% (eg, primidone) and which cannot be discontinued at least 4 weeks before Baseline or planned use at any time during the study.
• Use of prescription or nonprescription drugs, or other products (eg, grapefruit, grapefruit juice, or Seville oranges) known to be strong or moderate inhibitors of CYP3A4, that cannot be discontinued 2 weeks or 5 half-lives, whichever is longer, before Baseline or planned use at any time during the study.
• Use of proton pump inhibitors that cannot be discontinued at least 2 weeks before Baseline, or planned use at any time during the study. Occasional use of antacids or histamine-2 receptor antagonists will be permitted, but antacids should be taken at least 4 hours before or after study intervention; and histamine-2 receptor antagonists should be taken at least 4 hours after and at least 12 hours before study intervention.
• Inability to refrain from use of medication/substance(s) that might produce tremor or interfere with the evaluation of tremor on study visit days prior to discharge such as, but not limited to, stimulant decongestants, beta-agonist bronchodilators, and alcohol.
• Regular use of more than 3 units of alcohol per day.
• Regular consumption of caffeine > 400 mg/day or > 4 cups of coffee per day