Filed Pursuant to Rule 424(b)(3)

Registration No. 333-266136

PROSPECTUS SUPPLEMENT NO. 18

(To the Prospectus dated March 13, 2023)

Up to 10,916,647 Ordinary Shares Issuable Upon Exercise of Warrants

Up to 219,616,200 Ordinary Shares Offered by Selling Securityholders

Up to 4,666,667 Warrants to purchase Ordinary Shares offered by the Sponsor

This prospectus supplement supplements the prospectus, dated March 13, 2023 (the “Prospectus”), which forms a part of our registration statement on Form F-1 (No. 333-266136). This prospectus supplement is being filed to update and supplement the information in the Prospectus with certain of the information contained in our Report on Form 6-K filed with the Securities and Exchange Commission (the “SEC”) on June 29, 2023 (the “Report”). Accordingly, we have attached the Report to this prospectus supplement.

The Prospectus and this prospectus supplement relate to the issuance by us of 10,916,647 Ordinary Shares consisting of (i) 6,249,980 of our ordinary shares, $0.01 nominal value, (“Ordinary Shares”) that may be issued upon exercise of warrants to purchase Ordinary Shares at an exercise price of $11.50 (the “Public Warrants”), which were originally issued in the initial public offering of Oaktree Acquisition Corp. II (“OACB”) at a price of $10.00 per unit, with each unit consisting of one OACB Class A Ordinary Share (as defined in the Prospectus) and one-fourth of a Public Warrant, and (ii) 4,666,667 Ordinary Shares that may be issued upon exercise of warrants issued to Oaktree Acquisition Holdings II, L.P. (the “Sponsor”), and its transferees to purchase Ordinary Shares at an exercise price of $11.50 (the “Private Placement Warrants”). We refer to the Public Warrants and the Private Placement Warrants together as the “Warrants.”

The Prospectus and this prospectus supplement also relate to the offer and sale from time to time by the selling securityholders named in the Prospectus (collectively, the “Selling Securityholders”), or their permitted transferees, of up to (i) 17,493,000 Ordinary Shares subscribed for by the Selling Securityholders, for a subscription price of $10.00 per share, in the context of the PIPE Financing (as defined in the Prospectus), (ii) 6,250,000 Ordinary Shares issued to the Sponsor in exchange for OACB’s Class B Ordinary Shares, par value $0.0001 (which were purchased by the Sponsor for $25,000 or approximately $0.004 per share) in connection with the Business Combination (as defined in the Prospectus), (iii) 4,666,667 Ordinary Shares issuable upon exercise of Private Placement Warrants, (iv) 186,206,553 Ordinary Shares issued to former shareholders of Alvotech Holdings S.A. (“Alvotech Holdings”) in exchange for their Alvotech Holdings Ordinary Shares (as defined in the Prospectus) in connection with the Business Combination (subject to vesting and lockups) at an equity consideration value of $10.00 per share, (v) 5,000,000 Ordinary Shares subscribed for by Alvogen Lux Holdings S.à.r.l. and Aztiq Pharma Partners S.à.r.l., for a subscription price of $10.00 per share, in the context of the Alvogen-Aztiq Loan Advance Conversion (as defined in the Prospectus), and (vi) 4,666,667 Private Placement Warrants, which were purchased by the Sponsor at a price of $1.50 per warrant.

The Ordinary Shares and Warrants are listed on The Nasdaq Stock Market LLC (“Nasdaq”) under the symbols “ALVO” and “ALVOW,” respectively. On June 27, 2023, the closing price of the Ordinary Shares on Nasdaq was $7.45. The Ordinary Shares are also listed on the Nasdaq Main Market in Iceland (“Nasdaq Iceland Main Market”) under the symbol “ALVO.”

This prospectus supplement should be read in conjunction with the Prospectus, including any amendments or supplements thereto, which is to be delivered with this prospectus supplement. This prospectus supplement is qualified by reference to the Prospectus, including any amendments or supplements thereto, except to the extent that the information in this prospectus supplement updates and supersedes the information contained therein.

This prospectus supplement is not complete without, and may not be delivered or utilized except in connection with, the Prospectus, including any amendments or supplements thereto.

We are a “foreign private issuer” under applicable SEC rules and an “emerging growth company” as that term is defined in the Jumpstart Our Business Startups Act of 2012 and are eligible for reduced public company disclosure requirements.

You should read the Prospectus and any prospectus supplement or amendment carefully before you invest in our securities. Investing in our securities involves risks. See “Risk Factors” beginning on page 25 of the Prospectus and under similar headings in any amendments or supplements to the Prospectus.

Neither the SEC nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus supplement or the Prospectus. Any representation to the contrary is a criminal offense.

The date of this Prospectus Supplement No. 18 is June 29, 2023.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the Month of June 2023

Commission File Number: 001-41421

Alvotech

(Translation of registrant’s name into English)

9, Rue de Bitbourg,

L-1273 Luxembourg,

Grand Duchy of Luxembourg

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F:

☒  Form 20-F            ☐  Form 40-F

INFORMATION CONTAINED IN THIS REPORT ON FORM 6-K

Incorporation by reference

This Report on Form 6-K (this “Report”) of Alvotech (the “Company”), excluding Exhibit 99.1 attached hereto, shall be deemed to be incorporated by reference into the Company’s registration statement on Form S-8 (File No. 333-266881) and to be a part thereof from the date on which this Report is filed, to the extent not superseded by documents or reports subsequently filed or furnished.

Exhibit 99.1 to this Report is being furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act.

Press Release

On June 28, 2023, Alvotech issued a press release (“Press Release”) announcing that the U.S. Food and Drug Administration (“FDA”) has issued a complete response letter (“CRL”) for Alvotech’s Biologics License Application (“BLA”) for AVT02, a high-concentration biosimilar candidate for Humira^® (adalimumab), which contained data to support approval as a high-concentration biosimilar and additional information to support the interchangeability designation. The CRL noted that certain deficiencies, which were conveyed following the FDA’s reinspection of the company’s Reykjavik facility that concluded in March 2023, must be satisfactorily resolved before the application can be approved. A copy of the Press Release is furnished herewith as exhibit 99.1.

EXHIBIT INDEX

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Exhibit 99.1

Alvotech Provides Regulatory Update

on Second Biologics License Application for AVT02

REYKJAVIK, Iceland, June 28, 2023 (GLOBE NEWSWIRE) – Alvotech (NASDAQ: ALVO), a global biotech company specializing in the development and manufacture of biosimilar medicines for patients worldwide, announced today that the US Food and Drug Administration (FDA) has issued a complete response letter (CRL) for Alvotech’s second Biologics License Application (BLA) for AVT02, a high-concentration biosimilar candidate for Humira^® (adalimumab). As the second of two BLAs submitted for AVT02, this BLA contained data to support approval as a high-concentration biosimilar and additional information to support the interchangeability designation.

The CRL noted that certain deficiencies, which were conveyed following the FDA’s reinspection of the company’s Reykjavik facility that concluded in March 2023, must be satisfactorily resolved before the application can be approved. No other deficiencies in the application were noted by the FDA.

Alvotech intends to resubmit a BLA for AVT02, including data supporting an interchangeability designation, to the FDA, which would trigger a six-month review period and a new Biosimilar User Fee Act (BsUFA) date.

Due to the expected delay in the potential approval of AVT02 in the US, as a result of the communication received from the FDA, Alvotech will explore options to raise additional capital, in order to continue advancing pipeline development in the near-term. In addition to AVT02, the company is currently developing a pipeline of 7 disclosed and 3 undisclosed biosimilar candidates. The financing options which will be explored include, but are not limited to, equity financing, sale of convertible bonds or other forms of debt financing. ATP Holdings ehf., a subsidiary of Aztiq, the largest shareholder of Alvotech, has today declared its interest in providing Alvotech with up to $100 million in proceeds from potential financing.

“We remain committed to bringing AVT02 to patients in the US, where the need for a high-concentration, interchangeable biosimilar to Humira remains significant,” said Robert Wessman, Chairman and CEO of Alvotech. “We expect that a reinspection of our manufacturing facility will be required to gain approval in the US and anticipate a reinspection following resubmission of a BLA for AVT02.”

About AVT02

AVT02 is a monoclonal antibody and has been approved as a biosimilar to Humira^® (adalimumab) in several countries globally, including the 27 member states of the European Union, Norway, Lichtenstein, Iceland, the UK, Switzerland, Canada, Australia, and Saudi Arabia. It is currently marketed in multiple European countries and in Canada. Dossiers are also under review in multiple countries globally.

About Alvotech

Alvotech is a biotech company, founded by Robert Wessman, focused solely on the development and manufacture of biosimilar medicines for patients worldwide. Alvotech seeks to be a global leader in the biosimilar space by delivering high quality, cost-effective products, and services, enabled by a fully integrated approach and broad in-house capabilities. Alvotech’s current pipeline includes eight disclosed biosimilar candidates aimed at treating autoimmune disorders, eye disease, osteoporosis, respiratory disease, and cancer. Alvotech has formed a network of strategic commercial partnerships to provide global reach and leverage local expertise in markets that include the United States, Europe, Japan, China, and other Asian countries and large parts of South America, Africa and the Middle East. Alvotech’s commercial partners include Teva Pharmaceuticals, a US affiliate of Teva Pharmaceutical Industries Ltd. (US), STADA Arzneimittel AG (EU), Fuji Pharma Co., Ltd (Japan), Advanz Pharma (EEA, UK, Switzerland, Canada, Australia and New Zealand), Cipla/Cipla Gulf/Cipla Med Pro (Australia, New Zealand, South Africa/Africa), JAMP Pharma Corporation (Canada), Yangtze River Pharmaceutical (Group) Co., Ltd. (China), DKSH (Taiwan, Hong Kong, Cambodia, Malaysia, Singapore, Indonesia, India, Bangladesh and Pakistan), YAS Holding LLC (Middle East and North Africa), Abdi Ibrahim (Turkey), Kamada Ltd. (Israel), Mega Labs, Stein, Libbs, Tuteur and Saval (Latin America) and Lotus Pharmaceuticals Co., Ltd. (Thailand, Vietnam, Philippines, and South Korea). Each commercial partnership covers a unique set of product(s) and territories. Except as specifically set forth therein, Alvotech disclaims responsibility for the content of periodic filings, disclosures and other reports made available by its partners. For more information, please visit www.alvotech.com. None of the information on the Alvotech website shall be deemed part of this press release.

Forward-Looking Statements

Certain statements in this communication may be considered “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking statements generally relate to future events or the future financial operating performance of Alvotech and may include, for example, Alvotech’s expectations regarding competitive advantages, business prospects and opportunities including pipeline product development, future plans and intentions, results, level of activities, performance, goals or achievements or other future events, regulatory submissions, review and interactions, including the resubmission of a BLA for AVT02 and a potential reinspection of Alvotech’s manufacturing facility, the satisfactory responses to the FDA’s inspection findings and resolution of other deficiencies conveyed following the inspection of Alvotech’s manufacturing site, the potential approval and commercial launch of its product candidates, the timing of regulatory approval and market launches, the estimated size of the total addressable market of Alvotech’s pipeline products, the availability of financing options, including the size, timeline, securities, terms and conditions of, and use of proceeds from, a potential financing. In some cases, you can identify forward-looking statements by terminology such as “may”, “should”, “expect”, “intend”, “will”, “estimate”, “anticipate”, “believe”, “predict”, “potential”, “aim” or “continue”, or the negatives of these terms or variations of them or similar terminology. Such forward-looking statements are subject to risks, uncertainties, and other factors which could cause actual results to differ materially from those expressed or implied by such forward-looking statements. These forward-looking statements are based upon estimates and assumptions that, while

considered reasonable by Alvotech and its management, are inherently uncertain and are inherently subject to risks, variability, and contingencies, many of which are beyond Alvotech’s control. Factors that may cause actual results to differ materially from current expectations include, but are not limited to: (1) the outcome of any legal proceedings that may be instituted against Alvotech or others following the business combination between Alvotech Holdings S.A., Oaktree Acquisition Corp. II and Alvotech; (2) the ability to raise substantial additional funding, which may not be available on acceptable terms or at all; (3) the ability to maintain stock exchange listing standards; (4) changes in applicable laws or regulations; (5) the possibility that Alvotech may be adversely affected by other economic, business, and/or competitive factors; (6) Alvotech’s estimates of expenses and profitability; (7) Alvotech’s ability to develop, manufacture and commercialize the products and product candidates in its pipeline; (8) actions of regulatory authorities, which may affect the initiation, timing and progress of clinical studies or future regulatory approvals or marketing authorizations; (9) the ability of Alvotech or its partners to respond to inspection findings and resolve deficiencies to the satisfaction of the regulators; (10) the ability of Alvotech or its partners to enroll and retain patients in clinical studies; (11) the ability of Alvotech or its partners to gain approval from regulators for planned clinical studies, study plans or sites; (12) the ability of Alvotech’s partners to conduct, supervise and monitor existing and potential future clinical studies, which may impact development timelines and plans; (13) Alvotech’s ability to obtain and maintain regulatory approval or authorizations of its products, including the timing or likelihood of expansion into additional markets or geographies; (14) the success of Alvotech’s current and future collaborations, joint ventures, partnerships or licensing arrangements; (15) Alvotech’s ability, and that of its commercial partners, to execute their commercialization strategy for approved products; (16) Alvotech’s ability to manufacture sufficient commercial supply of its approved products; (17) the outcome of ongoing and future litigation regarding Alvotech’s products and product candidates; (18) the potential impact of the ongoing COVID-19 pandemic on the FDA’s review timelines, including its ability to complete timely inspection of manufacturing sites; (19) the impact of worsening macroeconomic conditions, including rising inflation and interest rates and general market conditions, war in Ukraine and global geopolitical tension, and the ongoing and evolving COVID-19 pandemic on the Company’s business, financial position, strategy and anticipated milestones; and (20) other risks and uncertainties set forth in the sections entitled “Risk Factors” and “Cautionary Note Regarding Forward-Looking Statements” in documents that Alvotech may from time to time file or furnish with the SEC. There may be additional risks that Alvotech does not presently know or that Alvotech currently believes are immaterial that could also cause actual results to differ from those contained in the forward-looking statements. Nothing in this communication should be regarded as a representation by any person that the forward-looking statements set forth herein will be achieved or that any of the contemplated results of such forward-looking statements will be achieved. You should not place undue reliance on forward-looking statements, which speak only as of the date they are made. Alvotech does not undertake any duty to update these forward-looking statements or to inform the recipient of any matters of which any of them becomes aware of which may affect any matter referred to in this communication. Alvotech disclaims any and all liability for any loss or damage (whether foreseeable or not) suffered or incurred by any person or entity as a result of anything contained or omitted from this communication and such liability is expressly disclaimed. The recipient agrees that it shall not seek to sue or otherwise hold Alvotech or any of its directors, officers, employees, affiliates, agents, advisors, or representatives liable in any respect for the provision of this communication, the information contained in this communication, or the omission of any information from this communication.

No Offer

This communication is not a public offer of securities for sale in the United States. This communication is for informational purposes only and does not constitute an offer to sell or a solicitation of an offer to buy any securities in the United States or elsewhere, nor shall there be any sale of any such securities in any state or jurisdiction in which such offer, solicitation, or sale would be unlawful prior to registration or qualification under the securities laws of such state or jurisdiction.

CONTACT INFORMATION

Alvotech Investor Relations and Global Communications

Benedikt Stefansson

alvotech.ir@alvotech.com