Forward-Looking Statements Certain statements set forth in this presentation constitute "forward-looking statements" within the meaning of the Private Securities Litigation Reform Act of 1995, as amended, including, but

Focus on Value Creation

Chief Executive Officer

39th Annual J.P. Morgan Healthcare Conference

January 13, 2021 Exhibit 99.1

Forward-Looking Statements Certain statements set forth in this presentation constitute "forward-looking statements" within the meaning of the Private Securities Litigation Reform Act of 1995, as amended, including, but not limited to, statements concerning: the company's mission of, and impact in, advancing cutting-edge science, developing innovative medicines, and addressing critical public health challenges; the company's expectations with respect to its current and future financial and operating performance, business plans or prospects, including potential growth of revenue from its commercial products, potential diversification of its product portfolio, therapeutic areas that the company may pursue and the company's plans to manage for growth and long-term profitability through execution of its Value Enhancement Plan, including its commitment to profitability targets, optimization of its cost structure and exploration of strategic opportunities; the potential therapeutic and commercial value of the company's marketed and development products; timelines, plans and expectations for development activities relating to the company's products and product development candidates in both neuroscience and oncology, including (i) for nemvaleukin alfa ("nemvaleukin"), plans to initiate additional studies with IV nemvaleukin, select additional tumor types to pursue, and explore strategic collaborations and (ii) for ALKS 1140, plans to begin phase 1 first-in-human trials; the company's expectations relating to regulatory activities and interactions, including the U.S. Food and Drug Administration's ("FDA") PDUFA target action date for the company's new drug application ("NDA") for ALKS 3831 and plans to advance discussions on registration plans for nemvaleukin with regulatory agencies; expectations concerning commercial activities relating to the company's products and product candidates, including preparations for the potential commercial launch of ALKS 3831 and the ability of the company's commercial model to drive growth and competitive advantage. The company cautions that forward-looking statements are inherently uncertain. These risks, assumptions and uncertainties include, among others: the potential impacts of the COVID-19 pandemic and efforts to mitigate its spread on the company's business, results of operations and financial condition; the unfavorable outcome of litigation, including so-called "Paragraph IV" litigation and other patent litigation, related to any of the company's products may lead to competition from generic drug manufacturers; data from clinical trials may be interpreted by the FDA in different ways than the company interprets it; the FDA may not agree with the company's regulatory approval strategies or components of the company's NDAs, including clinical trial designs, conduct and methodologies, manufacturing processes and facilities, or the adequacy of the data included in the NDAs to support the FDA's requirements for approval; the FDA or regulatory authorities outside the U.S. may make adverse decisions regarding the company's products, including with respect to the NDA for ALKS 3831; the company's development activities may not be completed on time or at all; the results of the company's development activities may not be positive, or predictive of real-world results or of results in subsequent trials, and preliminary or interim results of the company's development activities may not be predictive of final results of such activities, results of future preclinical or clinical trials or real-world results; the company and its licensees may not be able to successfully commercialize their products; there may be a reduction in payment rate or reimbursement for the company's products or an increase in the company's financial obligations to governmental payers; the company's products may prove difficult to manufacture, be precluded from commercialization by the proprietary rights of third parties, or have unintended side effects, adverse reactions or incidents of misuse; and those risks, assumptions and uncertainties described under the heading "Risk Factors" in the company's Annual Report on Form 10-K for the year ended Dec. 31, 2019, the company's quarterly report on Form 10-Q for the quarter ended June 30, 2020 and in subsequent filings made by the company with the U.S. Securities and Exchange Commission ("SEC"), which are available on the SEC's website at www.sec.gov and on the company's website at www.alkermes.com in the "Investors-SEC filings" section. Existing and prospective investors are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof. Except as required by law, the company disclaims any intention or responsibility for updating or revising any forward-looking statements contained in this presentation.

Note Regarding Trademarks: The company and its affiliates are the owners of various U.S. federal trademark registrations ( ) and other trademarks (TM), including ARISTADA , ARISTADA INITIO , VIVITROL , and LYBALVITM. VUMERITY is a registered trademark of Biogen MA Inc., used by Alkermes under license. Any other trademarks referred to in this presentation are the property of their respective owners. Appearances of such other trademarks herein should not be construed as any indicator that their respective owners will not assert their rights thereto.

Alkermes' Distinctive Mission 3 Advance cutting-edge science, develop innovative medicines, and engage in patient-focused advocacy to address critical public health challenges

Execution Against Our Strategic Priorities Commercial Execution VIVITROL and ARISTADA

Strong performance in a complex environment

Adapted commercial strategy in response to COVID-19

Prepared for synergistic launch of ALKS 3831 within psychiatry portfolio

Supported launch of VUMERITY Advancement of Highest Potential R&D Programs Completed successful Advisory Committee meeting for ALKS 3831*

Advanced nemvaleukin alfa (ALKS 4230) development program

Observed anti-tumor activity in monotherapy and combination settings with intravenous administration

Accelerated patient enrollment and expanded clinical trial network globally

Nominated first clinical candidate from HDAC** inhibitor program Efficient Management of Operating Structure and Strong Governance Adapted cost structure in response to COVID-19-related disruptions

Announced Value Enhancement Plan

Commitment to profitability targets

Focus on strategic opportunities

Continued Board refreshment

Appointed two new independent directors

Announced upcoming retirement of two long-serving directors

2020 Key Accomplishments *NDA resubmission under review following FDA Complete Response Letter and records requests relating to manufacturing of ALKS 3831. **HDAC: histone deacetylase

Focus on Value Creation in 2021: Three Key Components Grow and Diversify Commercial Revenues Demonstrate Value of R&D Investments Manage for Growth & Long-Term Profitability Drive VIVITROL and ARISTADA net sales

Support VUMERITY growth

Launch ALKS 3831 (PDUFA* June 1, 2021)

Determine registration pathway

Demonstrate anti-tumor activity

Explore strategic collaboration

ALKS 1140 (CoREST-selective HDAC inhibitor)

Initiate phase 1/FIH study

Provide update on pipeline platforms and programs Operationalize commitment to profitability targets

Optimize cost structure and drive operating leverage

Explore strategic opportunities to maximize value and enhance profitability

1 2 3 *Prescription Drug User Fee Act

Value Enhancement Plan and Board Refreshment Profitability Targets and Cost Structure Optimization Evaluation of Strategic Opportunities Board Refreshment Commitment to achieving:

Ongoing review to identify potential areas for improved efficiencies

Potential monetization or divestiture of non-core assets

Commitment to exploring strategic collaboration for immuno-oncology candidate (nemvaleukin) Appointed two new independent directors with strong financial and operational expertise

Plan to appoint at least one additional independent director in the first quarter of 2021 NGNI: Non-GAAP net income; EBITDA: Earnings before interest, tax, depreciation, amortization

Alkermes Commercial Model: Designed to Drive Growth and Competitive Advantage Dynamic Market Environment Alkermes Commercial Model Flexible and scalable

Allows for rapid adjustment to changes in healthcare landscape

Strong field presence supplemented by digital capabilities & non-personal promotion

Interactions with Federal and State policymakers Increased use of telepsychiatry**

Restricted access to healthcare providers**

Growing strength of government payers

Focus on pharmacoeconomic value

*Pending FDA approval

*Impacted by COVID-19 ALKS 3831

VIVITROL : Distinctive Product for a Major Public Health Need Extended-release opioid antagonist provides therapeutic levels of naltrexone for a one-month period

Indicated for the treatment of alcohol dependence

Indicated for the prevention of relapse to opioid dependence, following opioid detoxification Full prescribing information for VIVITROL may be found at www.vivitrol.com

VIVITROL Net Sales ($M) VIVITROL : Stabilization and Recovery Following COVID-19 Related Disruption VIVITROL Units (Four-week Average) COVID-19 disruptions began VIVITROL stabilization and recovery began *TTM (trailing 12 month) data includes Q4'19 through Q3'20 VIVITROL net sales.

VIVITROL : 2021 Focus Opioid Dependence (OD) Alcohol Dependence (AD) Focus on select settings of care to increase use of VIVITROL for the prevention of relapse to opioid dependence, following detoxification

Accelerate VIVITROL adoption in alcohol dependence by building on the growing use of medications

~14.5M 14% ~1.6M 90% of diagnosed AUD patients treated with MAT in 2019* people living with alcohol use disorder (AUD)* people living with opioid use disorder (OUD)* of diagnosed OUD patients treated with MAT in 2019* *2019 SAMHSA National Survey of Drug Use and Health. AD and OD (DSM-IV) (indications for VIVITROL) approximate moderate or severe AUD and OUD (DSM 5), respectively. Compton WM et al. Drug Alcohol Depend. 2013;132(1-2):387-390.

Full prescribing information for VIVITROL may be found at www.vivitrol.com

ARISTADA : LAI for Schizophrenia Suited for Today's Environment Long-acting injectable (LAI) atypical antipsychotic indicated for the treatment of schizophrenia

Novel molecular entity designed to address the real-world needs of patients and providers in the community Full prescribing information for ARISTADA may be found at www.aristada.com

ARISTADA TRx MOT Growth Outpaced the Atypical LAI Market ARISTADA TRx MOT Growth Rate TRx Data: IQVIA NPA data Nov R3

MOT: Months of therapy *TTM (trailing 12 month) data includes Q4'19 through Q3'20 ARISTADA net sales results. ARISTADA Net Sales ($M)

ARISTADA : A Unique Product Offering ARISTADA INITIO Regimen* ARISTADA 2-Month Dose Only long-acting treatment for schizophrenia that offers:

Single-day initiation

An option for dosing only six times a year *ARISTADA INITIO + single 30 mg oral dose of aripiprazole replaces need for concomitant three weeks of oral aripiprazole for initiation of ARISTADA, with relevant levels of aripiprazole concentration reached within four days. The first ARISTADA dose may be administered on the same day as ARISTADA INITIO or up to 10 days thereafter.

ORAL AAPs BIPOLAR I DISORDER Atypical Long-acting Injectable (aLAI) and Oral Atypical Antipsychotic (AAP) Markets Represent Large Opportunities aLAIs SCHIZOPHRENIA Branded Market Size* Annual TRx

(TTM)** Market Share** $3.2B ~2M 9% ARISTADA MOT Share $1.5B ~15M 21% olanzapine TRx Share $1.7B ~15M 12% olanzapine TRx Share ORAL AAPs SCHIZOPHRENIA * IQVIA NSP Audit SOB File Nov 2020

** IQVIA NPA Audit SOB File Nov 2020

IQVIA plan trak data, Q3 2020

IQVIA SOB Data, Q3 2020

MOT: Months of therapy Commercial Payer % 8% 20% 39%

LYBALVI * (ALKS 3831): A Potential New Oral Treatment for Adults With Schizophrenia and Adults With Bipolar I Disorder Daily oral investigational antipsychotic designed to offer efficacy of olanzapine; addition of samidorphan intended to mitigate olanzapine-associated weight gain

Fixed-dose combination

Bilayer tablet of samidorphan (10 mg) and olanzapine (5 mg, 10 mg, 15 mg, or 20 mg)

NDA resubmission under review by FDA; PDUFA date June 1, 2021

*The brand name LYBALVI has been conditionally accepted by the FDA and will be confirmed upon approval.

Alkermes Market Research Data Underscores Real-World Unmet Need and Opportunity OLZ is one of the most efficacious oral

AAPs for SZ OLZ is the most efficacious oral AAP for maintenance of BD 50% 71% Majority of HCPs Agree OLZ is One of the Most Efficacious Oral AAPs for SZ and BD* Weight Gain is Major Concern to SZ and BD Patients* 73% 82% Weight gain with olanzapine is a major concern to patients Schizophrenia and bipolar disorder patients cycle through 5-7 treatment options** on average

~70K treatment switches occur each month *Source: ALKS 3831 SZ & BD 2020 ATU; Fielded 2/3 - 3/6/2020; N=124 / 125 HCPs per SZ / BD study.

**Source: Market research study; Fielded May-June 2019; 26 BD-I patients, 10 SZ patients, 9 SZ caregivers.

Source: IQVIA SOB data for the oral atypical antipsychotic market, specific to SZ/BD indications.

HCPs: healthcare providers; OLZ: olanzapine; AAP: atypical antipsychotic; SZ: schizophrenia; BD: bipolar disorder

LYBALVI Focus: Drive Awareness and Plan for Launch in 2021 Launch Planning Awareness Engage in scientific exchange with healthcare providers

Continue disease state education campaign for caregivers, providers and thought leaders

Conduct investigational product presentations with payers

Target well-defined healthcare provider call universe at launch based on firsthand market insights

Leverage existing commercial organization

Implement patient access programs designed to mitigate payer restrictions early in launch

Neuroscience Oncology Research and Development Strategy: Focus on High-Value Candidates in Two Key Therapeutic Areas Psychiatry Neurology Engineered

Nemvaleukin Alfa ("nemvaleukin") Formerly referred to as ALKS 4230 Novel investigational immuno-oncology candidate designed to leverage proven anti-tumor effects of interleukin-2 (IL-2) pathway

Stable, inherently active, single polypeptide designed to selectively bind to the intermediate-affinity IL-2 receptor complex and expand tumor-killing CD8+ and Natural Killer (NK) T cells, and have negligible effects on Treg expansion

Activation of IL-2 Pathway Offers Broad Potential Clinical Utility IL-2 is a natural regulator of the activity of lymphocytes involved in the immune response

Recombinant human IL-2 as monotherapy can drive complete and durable responses in certain tumor types, but its toxicity profile significantly limits its broad use

A molecule with differentiated tolerability that targets the IL-2 pathway could be complementary to a wide range of other therapeutic approaches

Cancer antigen presentation

Vaccines IFN-a Anti-CD40 (agonist) TLR agonists 5 3 2 1 7 6 Infiltration of T cells into tumors

CAR-Ts Recognition of cancer cells by T cells

Chemotherapy Radiation Killing of cancer cells

Anti-PD-(L)1) Release of cancer cell antigens

Chemotherapy Radiation therapy Targeted therapy Priming and activation of Natural Killer and CD8+ T cells

CTLA4 Tumor Lymph node Blood vessel 4 Trafficking of T cells to tumors