Exhibit 12.1



Section 302 Certificate



Form of Certification Required by Rule 13a-14(a) or
15d-14(a) under the Securities Exchange Act of 1934 as Adopted Pursuant to Section 302 of the Sarbanes-Oxley Act of 2002



I, Justin Gover, certify that:



| | 1. | I have reviewed this annual report on Form 20-F of GW Pharmaceuticals plc;
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| | 2. | Based on my knowledge, this report does not contain any untrue statement of a material fact
    or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements
    were made, not misleading with respect to the period covered by this report;
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| | 3. | Based on my knowledge, the financial statements, and other financial information included
    in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the
    company as of, and for, the periods presented in this report;
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| | 4. | The company’s other certifying officer and I are responsible for establishing and
    maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal
    control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the company and have:
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| | a. | designed such disclosure controls and procedures, or caused such disclosure controls and
    procedures to be designed under our supervision, to ensure that material information relating to the company, including its
    consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this
    report is being prepared;
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| | b. | designed such internal control over financial reporting, or caused such internal control
    over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of
    financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted
    accounting principles;
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| | c. | evaluated the effectiveness of the company’s disclosure controls and procedures and
    presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end
    of the period covered by this report based on such evaluation; and
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| | d. | disclosed in this report any change in the company’s internal control over financial
    reporting that occurred during the period covered by the annual report that has materially affected, or is reasonably likely
    to materially affect, the company’s internal control over financial reporting; and
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| | 5. | The company’s other certifying officer and I have disclosed, based on our most recent
    evaluation of internal control over financial reporting, to the company’s auditors and the audit committee of the company’s
    board of directors (or persons performing the equivalent functions):
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| | a. | all significant deficiencies and material weaknesses in the design or operation of internal
    control over financial reporting which are reasonably likely to adversely affect the company’s ability to record, process,
    summarize and report financial information; and
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| | b. | any fraud, whether or not material, that involves management or other employees who have
    a significant role in the company’s internal control over financial reporting.
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Date: December 7, 2015



| | /s/ Justin Gover       
| | -----------------------
| | Justin Gover           
| | Chief Executive Officer