Notice of General Meeting and Follow-On Offering

GW Pharmaceuticals Files Registration Statement for Proposed Follow-OnOffering and Distributes Shareholder Circular and Notice of General Meeting

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London, UK, 20 December 2013: GW Pharmaceuticals plc (Nasdaq: GWPH, AIM: GWP, "GW" or the "Company"), a biopharmaceutical company focused on discovering, developing and commercialising novel therapeutics from its proprietary cannabinoid product platform, announced today that it has filed a registration statement with the U.S. Securities and Exchange Commission ("SEC") for a proposed public offering of American Depositary Shares ("ADSs") on the NASDAQ Global Market ("Nasdaq"). The number of shares to be offered and the price range for the offering have not yet been determined.

Since the initial public offering on Nasdaq earlier this year, GW has accelerated its research into cannabinoids in the treatment of epilepsy, with the emergence of a new epilepsy orphan development programme featuring a liquid formulation of highly purified cannabidiol (CBD) extract for which the trademark Epidiolex® has been registered. This programme has gained interest among U.S. based paediatric epilepsy specialists and patient organizations in the potential role of CBD in treating intractable childhood epilepsy, with initial focus on two orphan conditions, Dravet and Lennox-Gastaut syndromes, each of which are severe infantile-onset, drug-resistant epilepsy syndromes. The Directors believe the proposed offering would allow the Group to progress the development of Epidiolex as well as advance other epilepsy research programmes whilst retaining commercial rights to any products that may evolve from such programmes.

An explanatory circular has today been sent to all GW shareholders. The circular incorporates a letter from the Chairman and a Notice of Meeting convening a General Meeting to be held at 10:00 a.m. on 6 January 2014 in order for shareholders to vote upon the resolutions required to proceed with the proposed offering. The circular is now available on GW's website at www.gwpharm.com in the investor relations section.

Morgan Stanley & Co. LLC and Cowen and Company, LLC are acting as joint book-running managers for the offering. Piper Jaffray & Co. is acting as lead manager and Canaccord Genuity Inc. is acting as co-lead manager.

The proposed offering is subject to GW shareholder approval at a General Meeting which is expected to take place on 6 January, 2014. Although the final timing has yet to be determined, GW is aiming to complete the ADS offering in January 2014.

"Since our IPO on Nasdaq earlier this year, we have accelerated our research into cannabinoids in the treatment of epilepsy. Specifically, we have advanced a new childhood epilepsy orphan development programme centred on our product candidate Epidiolex, which has the potential to meet significant unmet needs in the treatment of orphan childhood epilepsy syndromes such as Dravet syndrome and Lennox-Gastaut syndrome," stated Justin Gover, GW's Chief Executive Officer. "This proposed fundraising is intended to enable GW to carry out the clinical development of Epidiolex as well as advance other epilepsy research programmes whilst allowing GW to retain full commercial rights to the product."

A registration statement relating to these securities has been filed with the SEC but has not yet become effective. When available, a copy of the preliminary prospectus may be obtained from Morgan Stanley & Co. LLC, Attention: Prospectus Department, 180 Varick Street, 2nd Floor, New York, New York 10014, or by email at [email protected], Attn: Syndicate Department, Telephone: (866) 718- 1649, from Cowen and Company, LLC, c/o Broadridge Financial Services, 1155 Long Island Avenue, Edgewood, NY,11717, Attn: Prospectus Department, Phone (631) 274-2806 / Fax (631) 254-7140; from Piper Jaffray & Co., Attention: Prospectus Department, 800 Nicollet Mall, J12S03, Minneapolis, MN 55402, or email at [email protected], Telephone: (800) 747-3924; from Canaccord Genuity Inc., Attention: Syndicate Department, 99 High Street, 12th Floor, Boston, Massachusetts 02110, or by telephone at (617) 371-3900.

This press release does not constitute a prospectus and does not constitute or form, and will not form, part of any offer or invitation to sell or issue, or the solicitation of an offer to purchase or acquire, any of the ordinary shares or ADSs or any other securities in the United States of America or in any other jurisdiction. Securities may not be offered or sold in the United States of America absent registration or an exemption from registration under the United States Securities Act of 1933, as amended (the "Securities Act"). Any public offering of securities to be made in the United States will be made by means of a prospectus. Such prospectus will contain detailed information about the issuer and its management and financial statements. This press release is being issued pursuant to and in accordance with Rule 135e under the Securities Act.

No money, securities or other consideration is being solicited, and, if sent in response to the information contained in this press release, will not be accepted.

Members of the public outside the United States will not be eligible to take part in the offering described above.

This press release is not directed to, or intended for distribution or use by, any person or entity that is a citizen or resident or located in any locality, state, country or other jurisdiction where such distribution, publication, availability or use would be contrary to law or regulation or which would require any registration or licensing within such jurisdiction.

The distribution of this press release into jurisdictions other than the UK may be restricted by law. Persons into whose possession this announcement come should inform themselves about and observe any such restrictions.

For readers in the European Economic Area

In any EEA Member State that has implemented the Prospectus Directive, this communication is only addressed to and directed at qualified investors in that Member State within the meaning of the Prospectus Directive. The term "Prospectus Directive" means Directive 2003/71/EC (and amendments thereto, including Directive 2010/73/EU, to the extent implemented in each relevant Member State), together with any relevant implementing measure in the relevant Member State.

For readers in the United Kingdom

This communication, in so far as it constitutes an invitation or inducement to enter into investment activity (within the meaning of s21 Financial Services and Markets Act 2000 as amended) in connection with the securities which are the subject of the offering described in this press release or otherwise, is being directed only at (i) persons who are outside the United Kingdom or (ii) persons who have professional experience in matters relating to investments who fall within Article 19(5) ("Investment professionals") of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005 (the "Order") or (iii) certain high value persons and entities who fall within Article 49(2)(a) to (d) ("High net worth companies, unincorporated associations etc") of the Order; or (iv) any other person to whom it may lawfully be communicated (all such persons in (i) to (iv) together being referred to as "relevant persons"). The ADSs are only available to, and any invitation, offer or agreement to subscribe, purchase or otherwise acquire such ADSs will be engaged in only with, relevant persons. Any person who is not a relevant person should not act or rely on this document or any of its contents.

About GW Pharmaceuticals plc

Founded in 1998, GW is a biopharmaceutical company focused on discovering, developing and commercializing novel therapeutics from its proprietary cannabinoid product platform in a broad range of disease areas. GW commercialized the world's first plant-derived cannabinoid prescription drug, Sativex®, which is approved for the treatment of spasticity due to multiple sclerosis in 24 countries. Sativex is also in Phase 3 clinical development as a potential treatment of pain in people with advanced cancer. This Phase 3 program is intended to support the submission of a New Drug Application for Sativex in cancer pain with the U.S. Food and Drug Administration and in other markets around the world. GW has a deep pipeline of additional cannabinoid product candidates, including Epidiolex which has received Orphan Drug Designation from the FDA for the treatment of Dravet syndrome, a severe infantile-onset, genetic, drug-resistant epilepsy syndrome. Our product pipeline also includes compounds in Phase 1 and 2 clinical development for glioma, ulcerative colitis, type‑2 diabetes, and schizophrenia. For further information, please visit www.gwpharm.com.

Forward-looking statements

This news release may contain forward-looking statements that reflect GWs current expectations regarding future events, including statements regarding the timing of and potential listing of American Depository Shares on the Nasdaq, the proposed timing of such offering and development and regulatory clearance of the GW's products. Forward-looking statements involve risks and uncertainties. Actual events could differ materially from those projected herein and depend on a number of factors, including (inter alia), the success of the GW's research strategies, the applicability of the discoveries made therein, the successful and timely completion of uncertainties related to the regulatory process, and the acceptance of Sativex®, Epidiolex® and other products and product candidates by consumer and medical professionals. A further list and description of risks, uncertainties and other risks associated with an investment in GW can be found in GW's filings with the U.S. Securities and Exchange Commission, including its most recent Form F-1. Existing and prospective investors are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof. GW undertakes no obligation to update or revise the information contained in this press release, whether as a result of new information, future events or circumstances or otherwise.

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