An AE is any untoward medical occurrence in a participant or clinical investigation participant administered a pharmaceutical product and that does not necessarily have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal assessment such as an abnormal laboratory value), symptom, or disease temporally associated with the use of a medicinal (investigational) product, whether or not related to the medicinal (investigational) product. TEAE is any AE that start or worsen on or after the date of first dose of study treatment. An SAE is any untoward medical occurrence that at any dose, results in death; in the view of the investigator places the participant at immediate risk of death; requires inpatient hospitalization or prolongation of existing hospitalization; results in persistent or significant disability/incapacity; results in a congenital anomaly/birth defect; is a medically important event.

Safety Analysis Set included all enrolled participants who received at least one dose of ALKS 8700.

Vital sign measurements included heart rate (low: <=50 beats per minute [bpm] and decrease >=15 bpm; High: >=120 bpm and increase >=15 bpm), systolic blood pressure (BP) (low: <=90 millimeters of mercury [mmHg] and decrease >=20 mmHg; High: >=180 mmHg and increase >=20 mmHg) and diastolic BP (low: <=50 mmHg and decrease >=15 mmHg; High: >=105 mmHg and increase >=15 mmHg).

Safety Analysis Set included all enrolled participants who received at least one dose of ALKS 8700. 'Number of Participants Analyzed' signifies number of participants analyzed for this outcome measure. 'Number Analyzed' signifies number of participants analyzed for the specified measurement.

Potentially clinically significant QTcF values (>450 to <=480 millisecond [msec], >480 to <=500 msec) at any post-baseline visit during treatment period were reported.

Safety Analysis Set included all enrolled participants who received at least one dose of ALKS 8700. 'Number of Participants Analyzed' signifies number of participants analyzed in this outcome measure.

The C-SSRS is a clinician-administered instrument that systematically assess suicidal ideation and behavior rating scale. It rates an individual's degree of suicidal ideation (SI) on a scale, ranging from "wish to be dead" to "active suicidal ideation with specific plan and intent." The scale identifies SI severity and intensity, which may be indicative of an individual's intent to commit suicide. C-SSRS SI severity subscale ranges from 0 (no SI) to 5 (active SI with plan and intent). The scale identifies specific behaviors ranging from "preparatory acts or behavior" to "suicide" which may be indicative of an individual's intent to complete suicide.

Safety Analysis Set included all enrolled participants who received at least one dose of ALKS 8700.

Laboratory assessments included hematology, biochemistry, and urinalysis. Abnormality criteria: >=3xupper limit of normal (ULN) in alanine aminotransferase, aspartate aminotransferase; In millimoles per liter (mmol/L) [bicarbonate<15/>31, chloride<=90, potassium<3/>5.5, sodium<130/>150]; In mg per decilitre(mg/dL) {total bilirubin>=2.0, calcium<8.2/>12, total cholesterol>300, creatinine>=2.0, glucose<50/>200, cholesterol: High density lipoprotein (HDL)<=30, low density lipoprotein (LDL)>=160, triglycerides>=120 [female(F)]/>=160 [male(M)], urate>9/>8(F), blood urea nitrogen>30}; >3xULN in creatine kinase, lactate dehydrogenase; Hematocrit <=32(F)/<=37(M) percentage(%),3 point decrease from baseline; Hemoglobin<=9.5(F)/<=11.5(M)g/dL; Lymphocytes<0.5x10^9/L; In 10^3/microliter(uL) [Eosinophils>1; Absolute neutrophils<1.5; Platelets<75.1/>=700; Leukocytes<=2.8/>=16]; Albumin/creatinine>200g/kilograms(kg); Beta-2 microglobulin >0.3milligrams/liter(mg/L); Glucose/protein at least 2+.

Safety Analysis Set included all enrolled participants who received at least one dose of ALKS 8700. 'Number of Participants Analyzed' signifies number of participants analyzed for this outcome measure. 'Number Analyzed' signifies number of participants analyzed for the specified measurement.

Relapse was defined as new or recurrent neurologic symptoms, not associated with fever or infection, lasting for at least 24 hours, accompanied by one or more of the following: New objective neurological findings upon examination by the treating neurologist that are functionally consistent with findings on the Expanded Disability Status Scale [EDSS] (performed within 7 days of onset of symptoms) with an increase over the prior visit of ≥ 0.5 for the total score, an increase of ≥ 2 in 1 functional system (FS), except bladder/cognitive changes, and/or, an increase of ≥ 1 in 2 FS, except bladder/cognitive changes. The relapse rate for an individual participant was calculated as the number of relapses for that participant divided by the number of participant-years followed. The ARR for each enrollment group was calculated as the total number of relapses experienced in the group divided by the total number of participant-years on study.

Safety Analysis Set included all enrolled participants who received at least one dose of ALKS 8700.

Relapse was defined as new or recurrent neurologic symptoms, not associated with fever or infection, lasting for at least 24 hours, accompanied by one or more of the following: New objective neurological findings upon examination by the treating neurologist that are functionally consistent with findings on the EDSS (performed within 7 days of onset of symptoms) with an increase over the prior visit of ≥ 0.5 for the total score, an increase of ≥ 2 in 1 FS, except bladder/cognitive changes, and/or, an increase of ≥ 1 in 2 FS, except bladder/cognitive changes.

Safety Analysis Set included all enrolled participants who received at least one dose of ALKS 8700.

The EDSS is used to measure and evaluate MS participants' level of functioning. The EDSS provides a total score on a scale that ranges from 0 to 10. The first levels 1.0 to 4.5 refer to people with a high degree of ambulatory ability and the subsequent levels 5.0 to 9.5 refer to the loss of ambulatory ability. The range of main categories include (0) = normal neurologic examination; to (5) = ambulatory without aid or rest for 200 meters; disability severe enough to impair full daily activities; to (10) = death due to MS. Higher scores indicate more disability. Positive change from baseline indicates more disability.

FAS included all participants who received at least one dose of ALKS 8700 and had at least one post-baseline efficacy assessment. 'Number Analyzed' signifies number of participants analyzed for this outcome measure at the specified timepoint.

The T25-FW is a reliable quantitative mobility and leg function performance test based on a timed 25-foot walk. The participant was directed to one end of a clearly marked 25-foot course and was instructed to walk 25 feet as quickly as possible, but safely. Participants were allowed to use assistive devices (canes, crutches, walkers) as needed. The time was calculated from when the lead foot crosses the start point to when the participant had reached the 25-foot mark. The task was immediately administered again by having the participant walk back the same distance. The score for the T25-FW was calculated as the average of the 2 completed trials. A negative change from Baseline indicates improvement.

FAS included all participants who received at least one dose of ALKS 8700 and had at least one post-baseline efficacy assessment. 'Number Analyzed' signifies number of participants analyzed for this outcome measure at the specified timepoint.

The EQ-5D-5L is an instrument designed to assess decrements in health. The EQ-5D-5L includes a VAS and a descriptive system that defines health in terms of 5 dimensions: Mobility, Self-Care, Usual Activities, Pain/Discomfort, and Anxiety/Depression. Each dimension has 5 response categories corresponding to the level of severity (i.e., no problems, slight problems, moderate problems, severe problems, and unable to/extreme problems). The EQ-5D-5L VAS records the participant's self-rated health on a vertical visual analogue scale numbered from 100 (best health imagined) to 0 (worst health imagined). Higher scores indicate good health. Positive change from baseline indicates improved health.

FAS included all participants who received at least one dose of ALKS 8700 and had at least one post-baseline efficacy assessment. 'Number of Participants Analyzed' signifies number of participants analyzed for this outcome measure. 'Number Analyzed' signifies number of participants analyzed for this outcome measure at the specified timepoint.

The EQ-5D-5L is an instrument designed to assess decrements in health. The EQ-5D-5L includes a VAS and a descriptive system that defines health in terms of 5 dimensions: Mobility, Self-Care, Usual Activities, Pain/Discomfort, and Anxiety/Depression. Each dimension has 5 response categories corresponding to the level of severity (i.e., no problems, slight problems, moderate problems, severe problems, and unable to/extreme problems). The 5-item index score is transformed into a utility score between 0 (worst health state) and 1 (best health state). Higher scores indicate good health. Positive change from baseline indicates improved health.

FAS included all participants who received at least one dose of ALKS 8700 and had at least one post-baseline efficacy assessment. 'Number of Participants Analyzed' signifies number of participants analyzed for this outcome measure. 'Number Analyzed' signifies number of participants analyzed for this outcome measure at the specified timepoint.

The SF-12 uses 12 questions to measure functional health and well-being from the study participant's perspective across eight domains: physical functioning, role, bodily pain, general health perceptions, vitality, social functioning, emotional role, and mental health. Mental and physical composite scores (MCS & PCS) are computed using the scores of twelve questions and range from 0 to 100, where a higher score indicates better health. Positive change from baseline indicates improved health.

FAS included all participants who received at least one dose of ALKS 8700 and had at least one post-baseline efficacy assessment. 'Number Analyzed' signifies number of participants analyzed for this outcome measure at the specified timepoint.

The time to onset of 12-week confirmed disability progression is defined as the time from baseline to the first disability progression that is confirmed at the next regularly scheduled visit ≥ 12 weeks after the initial disability progression. Disability progression is defined by one of the following: an EDSS increase of at least 1.5 points from baseline EDSS = 0, an EDSS increase of at least a 1.0 point from baseline EDSS between 1.0 and 5.5 (inclusive), or an EDSS increase of at least 0.5 points from baseline EDSS = 6.0.

FAS included all participants who received at least one dose of ALKS 8700 and had at least one post-baseline efficacy assessment. 'Number of Participants Analyzed' signifies number of participants analyzed for this outcome measure.

The definition of NEDA-3 encompasses a combination of the following 3 related measures of disease activity: No relapses, no confirmed disability progression sustained for 12 weeks as measured on EDSS, and no magnetic resonance imaging (MRI) disease activity, defined as no gadolinium-enhancing (GdE) lesions and no new or enlarging T2 lesions. The definition of NEDA-4 was the above definition of NEDA-3 with the addition of a mean annualized rate of brain volume loss of less than 0.4% where annualized rate of brain volume loss was derived from percentage brain volume change (PBVC) from baseline and was calculated as ([PBVC/100+1]^[365.25/days]-1) × 100.

Safety Analysis Set included all enrolled participants who received at least one dose of ALKS 8700. 'Number Analyzed' signifies number of participants analyzed for this outcome measure at the specified timepoint.