GW Announces UK Launch of World's First Prescription Cannabis Medicine

Sativex(R) Marketed to Treat Spasticity Associated with Multiple Sclerosis

PORTON DOWN, England, June 21, 2010 - GW Pharmaceuticals plc (GWP:AIM) today announces the UK launch
of Sativex(R), its Oromucosal Spray for the treatment of spasticity due to
Multiple Sclerosis (MS). Sativex(R) is the world's first prescription
cannabis medicine and the UK is the first country in the world to grant a
full regulatory authorization for the product.

Sativex(R) contains two cannabinoids or active ingredients -
THC (delta-9-tetrahydrocannabinol) and CBD (cannabidiol). It is the first
cannabinoid medicine derived from whole plant extracts from the cannabis
sativa plant.

Sativex(R), available as a prescription only medicine, was
developed by GW in specific response to calls from people with MS for a
prescription cannabis-based medicine. Today's launch means that MS patients
suffering the spasms and cramping associated with spasticity have access to a
new treatment option which has been shown to improve their symptoms where
current treatments have failed.

Sativex(R) is manufactured by GW under Home Office licence at
an undisclosed location in the UK. The medicine is being marketed in the UK
by GW's UK licensee, Bayer Schering Pharma.

Dr Geoffrey Guy, GW's Chairman, said: "The approval and launch
of Sativex(R) in the UK is the world's first full approval of a
cannabis-derived prescription medicine and the product of eleven year's
research by GW into the cannabinoid system. GW was founded with the primary
goal of developing a medicine to address the unmet needs of people with MS
and today's launch of Sativex(R) represents a welcome advance in MS symptom
treatment. This is also an historic moment for GW and marks the beginning of
the company's transition from late stage development company to a commercial
pharmaceutical business. Today's news validates our cannabinoid technology
platform and enables us to progress the development of our pipeline across a
range of therapeutic areas with increased confidence."

Under the terms of the agreement with Bayer, GW will receive a
GBP10m milestone payment in respect of the UK approval of Sativex(R).

Outside the UK, Sativex is expected to be approved in Spain
shortly. Further submissions will be made in additional European countries
during the second half of 2010 under the mutual recognition procedure.
Almirall S.A. will market Sativex in Europe (ex-UK).

A series of photo images in connection with this story are available to
download at www.fovea.tv and/or call Peter Corbin
on +44(0)20-70892627.

Enquiries:

    GW Pharmaceuticals plc                       (Today) +44-20-7831-3113
    Dr Geoffrey Guy, Chairman                            +44-1980-557000
    Justin Gover, Managing Director

    GW PR
    Financial Media: Ben Atwell / John Dineen            +44-20-7831-3113
    Other Media: Mark Rogerson                           +44-7885-638810

    Bayer Schering Pharma                                +44-7711-200384
    Cherry Wood / Kim Lemon (Liberation                  +44-7771-561079
    Communications)

    GW Advisers: Piper Jaffray Ltd                       +44-20-3142-8700
    Neil Mackison / Rupert Winckler

For the full release including Note to Editors please visit:
www.gwpharm.com

Enquiries: GW Pharmaceuticals plc, Dr Geoffrey Guy, Chairman, (Today) +44-20-7831-3113,, Justin Gover, Managing Director, +44-1980-557000 ; GW PR, Financial Media: Ben Atwell / John Dineen, +44-20-7831-3113 ; Other Media: Mark Rogerson, +44-7885-638810 ; Bayer Schering Pharma, +44-7711-200384 ; Cherry Wood / Kim Lemon (Liberation Communications), +44-7771-561079 ; GW Advisers: Piper Jaffray Ltd, Neil Mackison / Rupert Winckler, +44-20-3142-8700