UNITED STATES 
                  SECURITIES AND EXCHANGE COMMISSION 
                        Washington, D.C. 20549 
                                    
                                    
                             SCHEDULE 13G 
                                    
               Under the Securities Exchange Act of 1934 
                                    
                                    
                           (Amendment No. )* 
                                    
                                    
                          GW Pharmaceuticals plc 
                             (Name of Issuer) 
                                      
                             Ordinary Shares 
                      (Title of Class of Securities) 
                                      
                                36197T103 
                              (CUSIP Number) 
                                    
                              July 31, 2014 
         (Date of Event Which Requires Filing of this Statement) 
                                    
                                    
Check the appropriate box to designate the rule pursuant to which this 
Schedule is filed: 
[X] Rule 13d-1(b) 
[ ] Rule 13d-1(c) 
[ ] Rule 13d-1(d) 
 
 
*The remainder of this cover page shall be filled out for a reporting 
person's initial filing on this form with respect to the subject class 
of securities, and for any subsequent amendment containing information 
which would alter the disclosures provided in a prior cover page. 
 
The information required in the remainder of this cover page shall not 
be deemed to be "filed" for the purpose of Section 18 of the Securities 
Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of 
that section of the Act but shall be subject to all other provisions of 
the Act (however, see the Notes). 
                                    
                                    
                                    















CUSIP: 36197T103                                                Page 1 of 5 
<Page> 

                                    
 1   NAMES OF REPORTING PERSONS 
     I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY) 
     Capital Research Global Investors ** 
      
      
 2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE          
     INSTRUCTIONS)                                                 (a)     
                                                                      
                                                                    (b)     
 3   SEC USE ONLY 
      
      
 4   CITIZENSHIP OR PLACE OF ORGANIZATION 
      
     Delaware 

             5   SOLE VOTING POWER 
                   
                  24,585,840 

       
             6   SHARED VOTING POWER 
 NUMBER OF         
   SHARES         NONE 
BENEFICIALL        
 Y OWNED BY 
             7   SOLE DISPOSITIVE POWER 
    EACH           
 REPORTING        24,585,840 
   PERSON 
   WITH: 
             8   SHARED DISPOSITIVE POWER 
                   
                  NONE 
                   
 9   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 
      
     24,585,840          Beneficial ownership disclaimed pursuant to Rule 
     13d-4   


 10  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES 
     (SEE INSTRUCTIONS) 
      
      
 11  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 
      
     10.4%   

 12  TYPE OF REPORTING PERSON (SEE INSTRUCTIONS) 
      
     IA   

** A division of Capital Research and Management Company (CRMC)  






CUSIP: 36197T103                                                Page 2 of 5 
<Page> 

                  SECURITIES AND EXCHANGE COMMISSION 
                         Washington, DC 20549 
                                    
                             Schedule 13G 
               Under the Securities Exchange Act of 1934 
                                    
Amendment No.  
 
Item 1(a)     Name of Issuer: 
       GW Pharmaceuticals plc 
 
Item 1(b)     Address of Issuer's Principal Executive Offices: 
       Porton Down Science Park, Salisbury 
       Wiltshire, SP4 0JQ 
       United Kingdom 
        
Item 2(a)     Name of Person(s) Filing: 
       Capital Research Global Investors 
        
Item 2(b)     Address of Principal Business Office or, if none, 
       Residence: 
       333 South Hope Street 
       Los Angeles, CA 90071 
        
Item 2(c)     Citizenship:   N/A 
        
Item 2(d)     Title of Class of Securities: 
       Ordinary Shares 
        
Item 2(e)     CUSIP Number: 
       36197T103 
        
Item 3     If this statement is filed pursuant to sections 240.13d-1(b) 
       or 240.13d-2(b) or (c), check whether the person filing is a:  
       (e)      [X]     An investment adviser in accordance with 
            section 240.13d-1(b)(1)(ii)(E). 
        
Item 4     Ownership 
        
       Provide the following information regarding the aggregate 
       number and percentage of the class of securities of the issuer 
       identified in Item 1. 
        
        
       (a)    Amount beneficially owned: 
       (b)    Percent of class: 
       (c)    Number of shares as to which the person has: 
       (i)    Sole power to vote or to direct the vote: 
       (ii)   Shared power to vote or to direct the vote: 
       (iii)  Sole power to dispose or to direct the disposition of: 
       (iv)   Shared power to dispose or to direct the disposition of: 
        
       See page 2  
        
       Capital Research Global Investors is deemed to be the 
       beneficial owner of 24,585,840 shares or 10.4% of the 
       236,402,355 shares believed to be outstanding as a result of 
       CRMC acting as investment adviser to various investment 
       companies registered under Section 8 of the Investment Company 
       Act of 1940. 
CUSIP: 36197T103                                                Page 3 of 5 
<Page>         
       All shares reported are held in the form of American Depositary 
       Shares, each representing 12 Ordinary Shares. 
        
Item 5     Ownership of Five Percent or Less of a Class.  If this 
       statement is being filed to report the fact that as of the date 
       hereof the reporting person has ceased to be the beneficial 
       owner of more than five percent of the class of securities, 
       check the following: [ ] 
        
Item 6     Ownership of More than Five Percent on Behalf of Another 
       Person: One or more clients of Capital Research Global 
       Investors have the right to receive or the power to direct the 
       receipt of dividends from, or the proceeds from the sale of, 
       the Ordinary Shares of GW Pharmaceuticals plc.  Capital 
       Research Global Investors holds more than five percent of the 
       outstanding Ordinary Shares of GW Pharmaceuticals plc as of 
       July 31, 2014 on behalf of each of the following client(s):   
        
       SMALLCAP World Fund, Inc. 
 
Item 7     Identification and Classification of the Subsidiary Which 
       Acquired the Security Being Reported on By the Parent Holding 
       Company or Control Person: N/A 
        
Item 8     Identification and Classification of Members of the Group:  
       N/A 
        
Item 9     Notice of Dissolution of Group:  N/A 
        
Item 10     Certification 
        
       By signing below, I certify that, to the best of my knowledge 
       and belief, the securities referred to above were acquired and 
       are held in the ordinary course of business and were not 
       acquired and are not held for the purpose of or with the effect 
       of changing or influencing the control of the issuer of the 
       securities and were not acquired and are not held in connection 
       with or as a participant in any transaction having that purpose 
       or effect. 
        
     Signature 
        
       After reasonable inquiry and to the best of my knowledge and 
       belief, I certify that the information set forth in this 
       statement is true, complete and correct. 
 
        Date:          August 8, 2014 
                        
        Signature:     Timothy D. Armour*** 
        Name/Title:    Timothy D. Armour - Senior Vice President 
                       Capital Research Global Investors 
 
        
        
        




CUSIP: 36197T103                                                Page 4 of 5 
         ***By  /s/ Herbert Y. Poon 
               Herbert Y. Poon 
               Attorney-in-fact 
        
          Signed pursuant to a Power of Attorney dated January 28, 2014 
          included as an Exhibit to Schedule 13G filed with the 
          Securities and Exchange Commission by Capital Research Global 
          Investors on February 10, 2014 with respect to Allergan, Inc. 
           
                
                



















































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