Investor Presentation

Investor Presentation September 2018 2018 GW Pharmaceuticals plc All Rights Reserved

Disclaimers FORWARD-LOOKING STATEMENTS This presentation contains forward-looking statements that are based on our management s beliefs and assumptions and on information currently available to management. Forward-looking statements include information about our current expectations for future events, including potential results of operations, the timing of clinical trials, the timing of regulatory filings, the timing and outcomes of regulatory or intellectual property decisions, demand for our commercially available products and products in development and the clinical benefits, safety profile and commercial potential of Sativex and Epidiolex. These forward-looking statements are subject to known and unknown risks, uncertainties, assumptions and other factors that could cause our actual results, performance or achievements to be materially different than any future results, performance or achievements expressed or implied by the forward-looking statements. Forward-looking statements represent our management s beliefs and assumptions only as of the date of this presentation. You should read our most recent Annual Report, as filed on Form 20-F with the Securities and Exchange Commission, including the Risk Factors set forth therein and the exhibits thereto, and our subsequent filings with the Securities and Exchange Commission, completely and with the understanding that our actual future results may be materially different from what we expect. Except as required by law, we assume no obligation to update these forward-looking statements publicly, or to update the reasons actual results could differ materially from those anticipated in the forward-looking statements, even if new information becomes available in the future. GW Pharmaceuticals plc Investor Presentation 1

GW S VISION is to be the global leader in prescription cannabinoid medicines, developing and commercializing pharmaceutical products which address clear unmet needs GW Pharmaceuticals plc Investor Presentation 2

Greenwich Biosciences & GW Pharmaceuticals RESEARCH DEVELOPMENT COMMERCIALIZATION 20+ years experience in researching and developing novel Rx cannabinoid medicines >500 person in-house team with expertise in bringing drugs to regulatory approval in US and ROW 14 cannabinoids evaluated in pre-clinical research >80 peer-reviewed publications Cannabinoids exported to >35 countries for research >50 Phase 2/3 clinical trials >55,000 patient-years of human safety data Sativex approved in >25 countries (ex- US) for relief of MS spasticity The World Leader in Cannabinoid Science Epidiolex Approved by FDA MAA application accepted for review US commercial launch expected in Fall 2018, pending rescheduling EU commercial infrastructure build ongoing Increased scale commercial manufacturing in place for Epidiolex launch Connect Most Innovative New Product Award Submission for Epidiolex (cannabidiol) oral solution 3

Epidiolex (cannabidiol) oral solution Treatment-Resistant Epilepsy Overview Extensive CBD pre-clinical research since 2007 showing in vivo and in vitro efficacy Positive data from three Phase 3 placebo-controlled trials in initial target orphan indications of Dravet syndrome and Lennox-Gastaut syndrome (LGS) Publication of Dravet and LGS Phase 3 trial results in The New England Journal of Medicine and first LGS Phase 3 results in The Lancet Epidiolex approved by FDA on June 25, 2018, pending rescheduling, commercial launch expected in the Fall, 2018 EMA submission accepted for review, expected decision in Q1 2019 Novel mechanism of action in epilepsy - CBD does not act through cannabinoid (CB) receptors or sodium channels - Prime targets are GPR55 and adenosine reuptake, TRPV1 Significant patient and physician interest with over 2,000 patients now treated with Epidiolex Real-world experience in Epidiolex use - Data from >1,000 patients in compassionate use program show treatment effect and safety across a range of severe epilepsy types Active lifecycle management plan, including additional target orphan indications Epidiolex (cannabidiol) is an investigational product outside of the United States of America Connect Most Innovative New Product Award Submission for Epidiolex (cannabidiol) oral solution 4

Significant Unmet Need in Epilepsy 2.2 million US patients with epilepsy (~470,000 children) - ~ One third of patients are pharmacoresistant with seizures persisting despite multiple antiepileptic drugs (AEDs) Childhood-onset epilepsy - Multiple distinct orphan syndromes, almost none with a specific indicated therapy - Many syndromes highly resistant to currently available AEDs - Seizures continue into adulthood Dravet syndrome and LGS represent two of the most difficult-to-treat epilepsy syndromes - Multiple seizure types, developmental delay, high risk of SUDEP - Highly refractory even with current medications, polytherapy generally required Physicians seek new treatment options - Majority of physicians not satisfied with current therapeutic options Sources: Sander JW, Epilepsia. 1993;34(6):1007; Picot et al, 2008 ; Kwan P, Brodie MJ. N Engl J Med. 2000;342:314-319; Kwan P, Brodie MJ, CNS Spectr. 2004;9(2):110 3 Picot et al, 2008; Kwan P, Brodie MJ. N Engl J Med. 2000;342:314-319; Kwan P, Brodie MJ, CNS Spectr. 2004;9(2):110, Morgan Stanley research (2015) GW Pharmaceuticals plc Investor Presentation 5

The Epidiolex Story: A History of Milestone Achievements Q4 12 First child treated with Epidiolex Q2 14 FDA grants GW IND Formal GW CBD development program begins Q2-4 15 3 Phase 3 studies in Dravet and LGS started and enrolled Q2 2016 LGS 1 topline results TSC Phase 3 trial started Q4 2016 AES: Dravet 1 LGS 1 Q2 2017 Dravet trial results published in NEJM Dec 2017 Epidiolex MAA submission Feb 2017 Epidiolex MAA accepted for review June 25, 2018 Epidiolex approved by the FDA #1 Q1 14 EAPs (Expanded Access Programs) initiated Q4 14 Dravet 1 Part A started Q1 2016 Dravet 1 topline results Q3 2016 LGS 2 topline results Q2 2017 AAN: LGS 2 Oct 2017 Epidiolex NDA for Dravet and LGS Dec 2017 NDA accepted for review: mid-2018 PDUFA Jan 2018 LGS trial results published in The Lancet Q1 2018 2 nd LGS trial results published in NEJM 2,000 patients have been treated with Epidiolex Connect Most Innovative New Product Award Submission for Epidiolex (cannabidiol) oral solution 6

Epidiolex Expanded Access Program FDA authorized, physician-sponsored expanded access program (EAP) initiated in early 2014 - Children and young adults with multiple etiologies, all with treatment-resistant epilepsy - ~20 physician site EAPs and 6 US state sponsored EAP programs - Over 1,100 patients approved for treatment by FDA Most recent EAP data presented in abstracts at AES 2017 - Long-term (96-week) Epidiolex safety and treatment effect data - All Children and Adults with Treatment-Resistant Epilepsies (Bebin et al, 2017) - Patients with LGS & Dravet syndrome (Laux et al, 2017) - For both convulsive and total seizures, median % reductions and 50%, 75% and 100% responder rates were consistent across all time points - CBD was generally well tolerated, adverse events (AEs) were consistent with those seen in previous pivotal and expanded access reports AES 2017 EAP Median % Reduction in Seizures All Patients with TRE Convulsive Seizures Total Seizures Patients with LGS and Dravet Syndrome Only Convulsive Seizures Total Seizures GW Pharmaceuticals plc Investor Presentation 7

Epidiolex Clinical Program

Physician Sponsored GW Sponsored Solution: Epidiolex Clinical Program Overview 2015 2016 2017 2018 2019 Dravet Syndrome Phase 3 (n=120) Positive Phase 3 (n=186) Fully Recruited FDA approval on June 25 th, 2018 Lennox-Gastaut Syndrome Tuberous Sclerosis Complex Phase 3 (n=171) Positive Phase 3 (n=225) Positive NDA MAA Phase 3 (n=210) Recruiting FDA Approval MAA submission accepted Feb 18 with expected decision in Q1 2019 Childhood Epilepsy Syndromes Ongoing Treatment Data from >1,000 patients Other Epilepsies Greenwich makes Epidiolex available to the most needy patients through an innovative compassionate use program Connect Most Innovative New Product Award Submission for Epidiolex (cannabidiol) oral solution 9

Median % Reduction Median % Reduction Phase 3 Dravet 1 Syndrome Trial Principal Efficacy Results 45 40 35 30 25 20 15 10 5 p=0.0123 Convulsive Seizures 39 13 p=0.0052 41 16 40 35 30 25 20 15 10 5 p=0.0335 29 9 Total Seizures p=0.0234 37 10 0 Treatment Period Maintenance Period 0 Treatment Period Maintenance Period 20 mg/kg/day CBD (n=61) Placebo (n=59) Source: J. H. Cross, O. Devinsky, L. Laux, E. Marsh, I. Miller, R. Nabbout, I. Scheffer, E. Thiele, S. Wright, Cannabidiol (CBD) reduces convulsive seizure frequency in Dravet Syndrome: results of a multi-centered, randomized, controlled study, Abstract No 2.362, 2016, American Epilepsy Society Annual Meeting GW Pharmaceuticals plc Investor Presentation 10

Median % Reduction Median % Reduction Phase 3 LGS 1 (Single Dose Cohort) Trial Principal Efficacy Results 60 50 40 p=0.0135 44 Drop Seizures p=0.0096 49 50 45 40 35 30 p=0.0005 41 Total Seizures p=0.0004 45 30 20 10 22 20 25 20 15 10 5 14 15 0 Treatment Period Maintenance Period 0 Treatment Period Maintenance Period 20 mg/kg/day CBD (n=86) Placebo (n=85) Source: E. Thiele, M. Mazurkiewicz-Beldzinska, S. Benbadis, E. Marsh, C. Joshi, J. French, C. Roberts, A. Taylor, K. Sommerville, Cannabidiol (CBD) significantly reduces drop seizure frequency in Lennox Gastaut syndrome: results of a multicenter, randomized, double blind, placebo-controlled trial, Abstract No 1.377, 2016, American Epilepsy Society Annual Meeting GW Pharmaceuticals plc Investor Presentation 11

Median % reduction / 28 days % Patients Phase 3 LGS 2 (Multiple Dose Cohorts) Trial Principal Efficacy Results 50 45 40 35 30 25 20 15 10 5 0 Reduction in Drop Seizures 42 37 17 Treatment Period (Primary) 47 40 19 Maintenance Period p<0.01 70 60 50 40 30 20 10 0 * 62 Drop Seizure Responder Rates Treatment Period * 63 43 GW Pharmaceuticals plc Investor Presentation 12 40 36 25% 50% 75% CBD 20 mg/kg/day (n=76) CBD 10 mg/kg/day (n=73) Placebo (n=76) 5 CBD 20 mg/kg, 3 CBD 10 mg/kg, and 1 placebo patient achieved drop seizure freedom during maintenance Cannabidiol (CBD) Significantly Reduces Drop Seizure Frequency in Lennox-Gastaut Syndrome (LGS): Multi-Center, Randomized, Double-Blind, Placebo-Controlled Trial (GWPCARE3) A.D. Patel, O. Devinsky, J.H. Cross, V. Villanueva, E. Wirrell, K. VanLandingham, C. Roberts, D. Checketts, S. Zuberi, American Academy of Neurology Annual Meeting 15 25 * 11 * p<0.05 p<0.01 p<0.001 3

Phase 3 Safety Profile Consistent adverse reaction profile across pivotal trials. Most common AEs (>10% of patients) in Phase 3 trials include: - somnolence; decreased appetite; diarrhea; transaminase elevations; fatigue, malaise, and asthenia; rash; insomnia, sleep disorder and poor-quality sleep, and infections. - Warnings & Precautions related to hepatocellular injury and somnolence & sedation are included in the US Prescribing Information Low withdrawal rates seen throughout clinical program Elevations in hepatic transaminases have been reported, most commonly with concomitant valproate; none met criteria for serious liver injury; all elevations resolved most while on treatment - Physicians routinely monitor liver function in patients with epilepsy as there are a number of approved AEDs that are associated with elevations in transaminases - Monitoring recommendations and lower starting dose are included in US PI to help physicians manage potential liver risks Across the Phase 3 program, Epidiolex was generally welltolerated, with most AEs reported as mild or moderate GW Pharmaceuticals plc Investor Presentation 13

3rd Target Indication: Tuberous Sclerosis Complex (TSC) Selection of these indications driven by encouraging EAP data Tuberous Sclerosis Complex (~25,000 US TSC patients with treatment resistant seizures) - Single Phase 3 pivotal trial underway - TSC is a genetic disorder that results from a mutation in tumor suppressor genes genes TSC1 or TSC2 and causes non-malignant tumors to form in different organs (primarily the brain, eyes, heart, kidney, skin and lungs) - Of TSC patients with epilepsy, 70% experience seizure onset in their first year of life - Co-morbidities include: cognitive impairment (50%), autism spectrum disorders (up to 40%), neurobehavioral disorders (over 60%) Sources: Tuberous Sclerosis Alliance; Child Neurology Foundation; Infantile Spasms Project GW Pharmaceuticals plc Investor Presentation 14

Commercialization

Commercial Manufacturing Growing & Harvesting Drying & Processing Extraction Crystallisation (API) Drug Product Manufacture Bottling & Labeling Non-GMP GMP GW has operated under commercial Good Manufacturing Practices (GMP) licenses issued outside the US since 2005 Manufacturing scaled through in-house and 3 rd party facilities Further increases in scale anticipated in 2018 and beyond to meet anticipated global demand Regulatory evaluation same as small molecule, not botanical FDA pre-approval inspections completed with no form 483 citations GW Pharmaceuticals plc Investor Presentation 16

Epidiolex Commercial Exclusivity Orphan Designation 7 years in the US plus expected 6-month pediatric extension 10 years in the EU plus expected 2 years pediatric extension Intellectual Property Pursuing a patent strategy designed to have patents issued to protect lead drug candidate and other pipeline candidates beyond Orphan Designation Current portfolio includes multiple distinct patent families in the treatment of epilepsy and formulations To date, 8 patents granted by the USPTO (expiry to 2035) A number of these patents expected to be listed in the Orange Book Additional patent applications expected as new data is generated Life-cycle management through new indications, formulation improvements, combinations and additional commercial geographies Proposed new formulations include liquid, solid dose, intravenous Orphan Exclusivity Patent Protections Life-Cycle Management GW Pharmaceuticals plc Investor Presentation 17

Epidiolex Patent Portfolio (applications in public domain numerous patents filed and not yet available through USPTO website) Patent Primary Claim Status US 9,066,920 A method of treating partial seizure comprising administering CBD at a daily dose of at least 400mg. Granted US 9,522,123 A method of treating complex partial seizure comprising administering CBD at a daily dose of at least 400mg. Granted US 9,474,726 A method of treating febrile infection related epilepsy syndrome (FIRES) comprising administering CBD) to a subject. Granted US 9,956,184 A method of reducing seizure frequency in LGS with concomitant CBD and clobazam, wherein the CBD dose is 10 mg/kg/day or greater and the purity of the CBD is greater than 98%. US 9,949,937 US 9,956,183 US 9,956,186 US 9,956,185 US 15/449,402 US 15/449,535 A method of reducing seizure frequency in Dravet syndrome with concomitant CBD and clobazam, wherein the CBD dose is 10 mg/kg/day or greater and the purity of CBD is greater than 98%. A method of reducing seizure frequency in LGS or Dravet syndrome with concomitant CBD and clobazam, wherein the dose of clobazam is reduced and the purity of CBD is greater than 98%. A method of reducing convulsive seizures in LGS with CBD, wherein the CBD dose is 10 mg/kg/day or greater and the purity of CBD is greater than 98%. A method of reducing convulsive seizures in Dravet syndrome with CBD, wherein the CBD dose is 10 mg/kg/day or greater and the purity of CBD is greater than 98%. A method of reducing drop seizure frequency in treatment-resistant childhood-onset epilepsy with CBD, wherein the CBD dose is between 5-35 mg/kg/day and the purity of CBD is greater than 98%. A method of reducing drop seizure frequency in a patient with Lennox-Gastaut syndrome, comprising administering to the patient in need thereof cannabidiol (CBD), wherein the CBD has a purity of at least 98% (w/w) CBD and comprises not more than 0.15% (w/w) Δ9-tetrahydrocannabinol (THC); and wherein the dose of the CBD is about 20 mg/kg/day Granted Granted Granted Granted Granted Pending Pending GW Pharmaceuticals plc Investor Presentation 18

Epidiolex Rescheduling FDA approval necessitates that Epidiolex be moved out of Schedule I once it has an accepted medical use Effect on Subjective Pharmacodynamic Measures (1) At the time of NDA approval, FDA recommend the appropriate lower schedule based on the abuse liability data submitted as part of the NDA Following NDA approval, DEA has up to 90 days to issue an interim final rule (IFR) to reschedule, after which Epidiolex can be marketed and dispensed GW is aiming for Epidiolex to be placed into Schedule IV - MARINOL (synthetic THC in sesame oil) Schedule III (1) Assessment of the Abuse Potential of Cannabidiol in Recreational Polydrug Users: A Randomized, Double- Blind, Controlled Trial, Sommerville et al, 2017, Greenwich Biosciences, Inc. GW Pharmaceuticals plc Investor Presentation 19

Epidiolex Commercialization Status Global commercialization rights to Epidiolex fully-owned by GW Pharmaceuticals Group companies In the US we will use our subsidiary, Greenwich Biosciences Inc., to commercialize our products U.S. Launch Preparations - U.S. sales organization fully recruited comprising two national directors, eight regional managers plus 66 Neurology Account Managers - Active engagement with U.S. payors ongoing with clinical presentations to plans that cover over 80% of covered lives in the U.S. - U.S. supply chain platform in place which will employ a closed model distribution network of five Specialty Pharmacy Providers (SPP s) U.S. Launch expected Fall 2018 EU commercial footprint now in place in five major European markets in readiness for 2019 European launches GW Pharmaceuticals plc Investor Presentation 20

Additional Programs, Financial Information and Upcoming Milestones

GW s Cannabinoid Platform: A Proprietary Growth Engine Beyond Epidiolex Cannabis plant is a unique source of >100 cannabinoid molecules capable of targeting diseases across therapeutic areas and mechanisms - TRP channels, adenosine re-uptake, serotonin receptors, endocannabinoid system GW has a deep pipeline of additional cannabinoid product candidates Focus on orphan pediatric neurologic conditions within epilepsy, autism, NHIE, schizophrenia Existing physician relationships through Epidiolex program U.S. development and commercialization rights to Sativex fully owned by GW, plans underway to determine MS spasticity FDA regulatory pathway GW Pharmaceuticals plc Investor Presentation 22

Sativex - New U.S. Late Stage Pipeline Product Oromucosal spray of a formulated extract of cannabis that contains the principal cannabinoids delta-9- tetrahydrocannabinol (THC) and cannabidiol (CBD) in a 1:1 ratio Approved in >25 countries outside the United States for the treatment of spasticity due to Multiple Sclerosis (MS). Product is sold via marketing partners New placebo-controlled trial data presented at ECTRIMS 2017 positive primary and secondary endpoints GW reacquired full rights to develop and commercialize Sativex in U.S. (December 2017). Previous license agreement with Otsuka terminated Represents a new wholly-owned late-stage U.S. asset We expect to evaluate the optimal route to achieve a NDA GW Pharmaceuticals plc Investor Presentation 23

CBDV Program CBDV in Autism Spectrum Disorders - Pre-clinical research shows promising signals on cognitive/social endpoints as well as repetitive behavior - A physician-led, FDA authorized, expanded access IND to treat seizures associated with autism in 10 patients underway - An investigator-led 100 patient placebo-controlled trial in autism is also due to commence in Q3 2018 - Rett syndrome - Orphan Drug Designation from FDA for CBDV for the treatment of Rett syndrome - Open-label study in Rett Syndrome expected to commence in Q3 2018 - Phase 2 placebo-controlled trial expected to commence Q4 2018 CBDV in epilepsy (GWP42006) - CBDV looks to be differentiated from CBD in four key ways: efficacy profile in seizure models, metabolic profile, pharmacological profile and has different physico-chemical characteristics - CBDV has shown anti-epileptic properties across a range of in vitro and in vivo animal models of epilepsy - Phase 2a placebo-controlled trial (n=162) in adult patients with partial-onset epilepsy failed to differentiate from placebo on the primary endpoint as both arms showed reductions in focal seizures of approximately 40% - CBDV was generally well-tolerated with the majority of CBDV patients experiencing adverse events of mild or moderate severity - GW will continue to explore potential development opportunities for CBDV in the field of epilepsy GW Pharmaceuticals plc Investor Presentation 24

Recurrent Glioblastoma Multiforme (GBM) Program THC:CBD investigational product candidate for the treatment of GBM - Orphan Drug Designation from FDA GBM is the most common and most aggressive type of malignant primary brain tumor 1,2 - Typically patients succumb to the disease approximately 15 months after diagnosis - Treatment for GBM remains challenging and additional safe and effective long-term treatment options are needed - Standard treatment is surgical resection, radiotherapy and concomitant adjunctive chemotherapy Phase 2 study completed - THC:CBD + TMZ had an 83% one year survival rate compared with 44% for patients on placebo (TMZ only) (p=0.042) - Median survival for the THC:CBD group was over 662 days compared with 369 days in the placebo group 3 - THC:CBD was generally well tolerated with treatment emergent adverse events leading to discontinuation in two patients in each group - The most common adverse events (three patients or more and greater than placebo) were vomiting (75%), dizziness (67%) nausea (58%), headache (33%), and constipation (33%) 1. National Brain Tumor Society web site. "Tumor Types." http://www.braintumor.org/brain-tumor-information/understanding-brain-tumors/tumor-types/#glioblastoma-multiforme. 2. American Brain Tumor Association. (2012) "Glioblastoma and Malignant Astrocytoma." http://www.abta.org/secure/glioblastoma-brochure.pdf 3. Data reported by GW Pharmaceuticals press release 7 February 2017 GW Pharmaceuticals plc Investor Presentation 25

Key Financial Data Clean up ICON Cash at 30 June 2018 H2 2018 cash outflow guidance ($10-$20m Capex for manufacturing expansion $440.2m $120m $140m Share Capital Current Options Fully Diluted ADS/m 28.3 1.2 29.5 GW Pharmaceuticals plc Investor Presentation 26

Upcoming Milestones/Newsflow Expected Timing EPIDIOLEX REGULATORY DEA rescheduling Q3 2018 U.S. launch Fall 2018 EMA decision Q1 2019 EPIDIOLEX DATA Phase 3 tuberous sclerosis complex trial data H1 2019 2 nd Phase 3 Dravet syndrome trial data Q4 2018 EPIDIOLEX EXCLUSIVITY Track One patent decisions Ongoing PIPELINE Epidiolex in Rett syndrome IND Q4 2018 CBDV investigator-led placebo control trial in autism start Q3 2018 CBDV open label in Rett syndrome trial start Q3 2018 FDA meeting to determine Sativex NDA requirements H2 2018 CBDV Phase 2 Rett syndrome trial start Q4 2018 GW Pharmaceuticals plc Investor Presentation 27

Thank You GW Pharmaceuticals plc NASDAQ: GWPH Stephen Schultz, VP Investor Relations sschultz@gwpharm.com + 1 401-500-6570