Holding(s) in Company

TR-1: NOTIFICATION OF MAJOR INTEREST IN SHARES

1. Identity of the issuer or the underlying issuerof existing shares to which voting rights areattached: ii

GW Pharmaceuticals PLC

2 Reason for the notification (please tick the appropriate box or boxes):

An acquisition or disposal of voting rights

An acquisition or disposal of qualifying financial instruments which may result in the acquisition of shares already issued to which voting rights are attached

An acquisition or disposal of instruments with similar economic effect to qualifying financial instruments

An event changing the breakdown of voting rights

x

Other (please specify):

Change of custodian

3. Full name of person(s) subject to thenotification obligation: iii

Farallon Capital Management L.L.C

4. Full name of shareholder(s)  (if different from 3.):iv

N/A

5. Date of the transaction and date onwhich the threshold is crossed orreached: v

9 May 2013

6. Date on which issuer notified:

9 May 2013

7. Threshold(s) that is/are crossed orreached: vi, vii

5%

8. Notified details:

A: Voting rights attached to shares viii, ix

Class/type ofshares

if possible usingthe ISIN CODE

Situation previousto the triggeringtransaction

Resulting situation after the triggering transaction

NumberofShares

NumberofVotingRights

Numberof shares

Number of votingrights

% of voting rights x

Direct

Direct xi

Indirect xii

Direct

Indirect

B: Qualifying Financial Instruments

Resulting situation after the triggering transaction

Type of financialinstrument

Expirationdate xiii

Exercise/Conversion Period xiv

Number of votingrights that may beacquired if theinstrument isexercised/ converted.

% of votingrights

American depository US36197T1034

Below 5%

Below 5%

C: Financial Instruments with similar economic effect to Qualifying Financial Instruments xv, xvi

Resulting situation after the triggering transaction

Type of financialinstrument

Exercise price

Expiration date xvii

Exercise/Conversion period xviii

Number of voting rights instrument refers to

% of voting rights xix, xx

Nominal

Delta

Total (A+B+C)

Number of voting rights

Percentage of voting rights

Below 5%

Below 5%

9. Chain of controlled undertakings through which the voting rights and/or thefinancial instruments are effectively held, if applicable: xxi

Proxy Voting:

10. Name of the proxy holder:

11. Number of voting rights proxy holder will ceaseto hold:

12. Date on which proxy holder will cease to holdvoting rights:

13. Additional information:

The underlying shares to which the ADRs described in section 8. B above relate have now been admitted to trading on the Alternative Investment Market and the issuer has made a total voting rights announcement reflecting the newly issued shares. Therefore, while the ADS position has not changed, the percentage of the issuer's total voting rights represented by that position has, as a result of the admission of the new shares to trading, dropped below 5%.

14. Contact name:

Elizabeth Wallace

15. Contact telephone number:

+ 1 415 421 2132