GW Pharmaceuticals Investor Presentation

May 2020 NASDAQ: GWPH

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 and approvals, 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 and potential pricing of Sativex®, Epidiolex®, and any product candidates. These forward-looking statements are subject to known and unknown risks, uncertainties, assumptions, including those associated with COVID-19 pandemic, 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 filings with the Securities and Exchange Commission including our Transition Report on Form 10-K and our Quarterly Reports on Form 10-Q, 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.

May 2020 GW Pharmaceuticals Investor Presentation 2 2019/2020 Key Achievements

✓ Positive Epidiolex Phase 3 data for ✓ Highly successful Epidiolex® launch seizures in TSC 2019 total revenue of $296 million FDA/EMA TSC submissions completed in ✓ EU approval of Epidyolex® and initial 2020 (accepted for Priority Review by FDA commercial launches with July 31 PDUFA date) ✓ Epidiolex Phase 3 study in Rett syndrome commenced ✓ Epidiolex manufacturing and supply chain running smoothly ✓ Epidiolex exclusivity strengthened through 9 Orange Book-listed patents

✓ Nabiximols US pivotal clinical plan ✓ Advanced programs in schizophrenia, developed and ready to commence autism and NHIE in H2 2020

May 2020 GW Pharmaceuticals Investor Presentation 3 GW Leadership 20+ Years Expertise | Proven Track Record

MANUFACTURING REGULATORY PIPELINE

CLINICAL COMMERCIALIZATION PEOPLE We received a call from a mother/caregiver requesting — through tears — that we give a BIG Thank You to all involved with the Epidiolex® Program! “This is the most hope I’ve had for my daughter in years!”

• First FDA-approved plant-derived cannabinoid • Launched in the US on November 1, 2018 • New mechanism of action in epilepsy • Positive data from five consecutive Phase 3 RCTs • Indicated to treat seizures associated with LGS or Dravet syndrome in patients 2 years of age and older • Descheduled by DEA • TSC sNDA filing accepted for Priority Review

Epidiolex® (cannabidiol) Oral Solution FDA Approves First Medicine Derived From Cannabis Plant

In a historic first, the FDA approved the first-ever drug containing an active ingredient derived naturally from cannabis.

For the first time, FDA has approved a drug derived from the marijuana plant. The unprecedented move is designed to help patients with a rare form of epilepsy.

The approval marks the first time patients THE 50 GENIUS will have access in the U.S. to a cannabis- COMPANIES OF 2018 derived drug that has undergone a safety and efficacy review by the FDA.

May 2020 GW Pharmaceuticals Investor Presentation 6 A Strong Launch for

• Total Q1 2020 net product sales of $116.1M • Full-year 2019 net product sales of approximately $296.4M • Clinical performance strong and consistent with trials • High level of awareness and intent to prescribe • Payer coverage • Early coverage set foundation for strong launch • Coverage has evolved during the year in a favorable way

May 2020 GW Pharmaceuticals Investor Presentation 7 GW Net Sales Revenue Growth

140 $120.6 M 120 $109.1 M

100 $91.0 M

80 $72.0 M (Millions) 60

$39.2 M 40

20 $6.7 M

0 Q4 2018 Q1 2019 Q2 2019 Q3 2019 Q4 2019 Q1 2020

May 2020 GW Pharmaceuticals Investor Presentation 8 Epidiolex 2020: The Next Phase in Building a Blockbuster

Build on positive physician Accelerate Further experiences adoption Continue Continue to indication to increase across a partnerships minimize development prescribing to broader with payers to logistical Enter long- Execute on appropriate prescriber expand barriers to term care the TSC label patients base access Epidiolex segment expansion

May 2020 GW Pharmaceuticals Investor Presentation 9 Evolution of Y1 Coverage Exceeded Our Goal

97% of All US Insured Patients Have Epidiolex Coverage for LGS and Dravet Syndrome

Epidiolex Access 100 90 80 70 60 50 40 30 20 10 0 Launch 1/1/2019 6/1/2019 12/1/2019

Open Access PA to Indication Restrictive PA Non-Formulary

May 2020 GW Pharmaceuticals Investor Presentation 10 Express Scripts (ESI) Coverage of Epidiolex

• ESI is one of the two largest PBMs in the US • Coverage was decided soon after the launch • Epidiolex is a Preferred brand with lowest brand copay • Recent re-alignment of PBM clients creates opportunities for 2020 • Model for other payers’ evolution in 2020+

May 2020 GW Pharmaceuticals Investor Presentation 11 2020 Payer Focus

• Sharing real-world utilization trends and breadth of published evidence • Identifying unmet medical needs in epilepsy • Communicating clinical efficacy and safety • Highlighting the hidden cost of therapy interruption • Evaluating the cost of “managing” Epidiolex • Studying the economic outcomes of controlled epilepsy

PAYER NEWSLETTER LAUNCHED JANUARY 2020

May 2020 GW Pharmaceuticals Investor Presentation 12 EU Launch Update: Epidyolex® (cannabidiol)

• Approved in September 2019

• First wave of launches in 5 major markets • German commercial launch in Q4 2019 • Secured positive NICE recommendation in the UK with commercial launch in Q1 2020 • Commercial launches in France, Spain and Italy expected later this year, following pricing and reimbursement

• Early Access Program included >1,100 patients and >400 physicians from 250 top epilepsy centers across 5 major markets

• Plans in place for progression of pricing and reimbursement in second wave of 10 EU markets

May 2020 GW Pharmaceuticals Investor Presentation 13 Epidiolex in TSC: Effective and Well-Tolerated

• Safety profile observed consistent with previous studies, no new safety risks identified 52 50 49 48 • Lower incidence of known adverse events and laboratory changes in the 25 32 mg/kg/day group compared 27 with 50 mg/kg/day

• Label expansion discussions with the FDA to focus on 25 mg/kg dose, close to the dose range in the US prescribing information

Source: American Epilepsy Society Annual Meeting 2019 poster: Cannabidiol (CBD) Treatment in Patients with Seizures Associated with Tuberous Sclerosis Complex: A Randomized, Double blind, Placebo Controlled Phase 3 Trial (GWPCARE6); Thele et al

May 2020 GW Pharmaceuticals Investor Presentation 14 High Unmet Need in Patients Living With TSC

• sNDA submission accepted with Priority Review, July 31 PDUFA • EMA submission accepted for review “Some of the most • Epilepsy is present in >90% of patients with TSC challenging and frustrating aspects of tuberous sclerosis • TSC affects 40-50K in the US and 1-2M worldwide complex (TSC) are seizures that cannot be effectively • >60% of individuals with seizures associated with TSC controlled by existing do not achieve seizure control with standard treatments medications. Having a new safe and effective treatment • Leading cause of genetic epilepsy, often occurring in first option such as Epidiolex is year of life as focal seizures or infantile spasms desperately needed.”

Kari Luther Rosbeck President and CEO

Source: Tuberous Sclerosis Alliance; Child Neurology Foundation; Infantile Spasms Project

May 2020 GW Pharmaceuticals Investor Presentation 15 Significant Unmet Need in Treatment Resistant Epilepsy

~15-20K ~30-50K ~40-50K ~160K ~1M Dravet Lennox-Gastaut Tuberous sclerosis Treatment-resistant pediatric Treatment syndrome syndrome complex epilepsy patients resistant epilepsy Approved to treat the seizures associated with LGS and Dravet syndrome

seizures persisting despite multiple anti-epileptic drugs

Camfield CS, et al. Epilepsia. 1996;37(1):19-23; US Department of Commerce. https://www.census.gov/prod/3/98pubs/p23-194.pdf. 1997. Accessed May 29, 2018.; Camfield P, (AEDs) Camfield C. Epilepsia. 2007;48(6):1128-1132.; Berg AT, et al. Epilepsia. 2000;41(10):1269-1275.; Wu YW, et al. Pediatrics. 2015;136(5):e1310-e1315.; Centers for Disease Control. https://www.cdc.gov/mmwr/volumes/66/wr/mm6631a1.htm. 2017. Accessed April 19, 2018.; Kwan P, Brodie MJ. N Engl J Med. 2000;342:314-319; 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

May 2020 GW Pharmaceuticals Investor Presentation 16 Epidiolex® Patent Portfolio to 2035 Aligns with Indication

FDA-approved to treat seizures associated with Lennox-Gastaut Syndrome or Dravet syndrome in patients 2 years of age and older

US15/183947 US9956186 US9956184 US10111840 US10137095 Treatment of US10195159 Treatment of Treatment of Treatment of Treatment of focal seizures in Formulation of EXP convulsive EXP seizures in LGS EXP atonic seizures in EXP EXP EXP drop seizures in Dravet syndrome cannabinoid-rich seizures in LGS with about at least Dravet syndrome 2020 2035 2035 2035 LGS with about 2035 with 15-20mg/kg/ day TDB extract with at least 10mg/kg/day of CBD LGS with about 20mg/kg/day of CBD of CBD 10mg/kg/day of CBD and clobazam 20mg/kg/day of CBD Awaiting Grant

US9956183 US9956185 US9949937 Treatment of US10603288 Treatment of US10092525 Treatment of seizures in Epidiolex treatment convulsive EXP EXP Treatment of seizures in Dravet syndrome EXP PCT/GB2019/051173 of seizures in LGS EXP seizures in Dravet drop seizures in EXP EXP w/CBD at 2035 Dravet syndrome 2035 or LGS with Epidiolex syndrome with at 2035 Dravet syndrome 5mg/kg/day 2035 with about at least clobazam or CBD in 2035 composition patent 2039 least 10mg/kg/day of with about increasing in 10mg/kg/day of CBD a patient previously application CBD and clobazam 20mg/kg/day of CBD increments of 2 to treated with 5mg/kg/day. clobazam

9 Orange Book-listed patents to date plus formulation, TSC, and use patents in prosecution plus additional applications planned

May 2020 GW Pharmaceuticals Investor Presentation 17 Nabiximols (known as Sativex® ex-US) Nabiximols: GW’s Next US Commercial Opportunity

Overlay of 24 Nabiximols Chromatograms: • Nabiximols US Adopted Name (USAN) Standardized “Full Spectrum” Composition • A complex botanical medicine formulated from extracts of the cannabis sativa plant that contains the principal cannabinoids THC and CBD and also contains minor constituents including related cannabinoid and non-cannabinoid plant components, such as terpenes, sterols, and triglycerides • Strong exclusivity due to complex botanical formulation • Near-term, reduced risk opportunity • Approved in >25 countries outside the US as Sativex® for the treatment of spasticity due to multiple sclerosis (MS); sold via marketing partners • US commercial rights owned by GW

May 2020 GW Pharmaceuticals Investor Presentation 19 Nabiximols: Demonstrated Efficacy in MS Spasticity Supplementary Clinical Program for FDA Commencing in 2020

Efficacy demonstrated in 3 positive pivotal 3 trials conducted in Europe

GWMS0106 GWSP0604 SAVANT (n=189) (n=241) (n=106)

Numerical Rating Scale - Spasticity (NRS) mean change from baseline

Difference vs Placebo -0.52 (-1.029, -0.004) -0.84 (-1.29, -0.40) -1.90 (-2.73, -1.06) (95% CI)

P-value 0.048 0.0002 <0.0001

Collin, et al. Eur J Neurol 2007; 14: 290-96 Novotna, et al. Eur J Neurol 2011; 18(9): 1122-31 Markovà, et al. Int J Neursci 2019; 129(2):119-128

FDA meetings held to agree clinical and CMC requirements

• Phase 3 trial protocol finalized • Two 30 patient “mechanistic” studies • Trial to commence H2 2020 • To commence H2 2020 • 450 patients; Sites in US and Europe • CMC data in place

May 2020 GW Pharmaceuticals Investor Presentation 20 Nabiximols US Market Opportunity in MS Spasticity

• Spasticity occurs in up to 84% of MS patients Nabiximols Opportunity • Strong physician and • Despite current treatment, 1/3 live with uncontrolled spasticity patient enthusiasm for product use • 90% of physicians and • No new oral anti-spasticity medicines approved in over 20 years; patients highly to MS disease modifying treatments do not relieve MS symptoms moderately interested • US market potential • Spasticity significantly impacts daily function — reduced mobility estimated to be >$400 and inability to perform daily tasks, including walking and driving million

• 26–50% of MS patients are self-medicating with cannabis

Sources: 2014 NARCOMS survey, Rizzo et al. Mult Scler 2004, Rizzo et al. Mult Scler 2004

May 2020 GW Pharmaceuticals Investor Presentation 21 Significant Lifecycle Opportunities for Nabiximols

Second target indication: Spasticity associated with Spinal Cord Injury (SCI) • Approx. 250K chronic SCI patients (~65%) suffer from spasticity • Likely single pivotal trial required • Sales potential >$400M

Further opportunities to address broader spasticity population • Spasticity occurs in >3M U.S. patients including spinal cord injury, post-stroke, ALS, traumatic brain injury, cerebral palsy

Additional target indication: Post Traumatic Stress Disorder (PTSD) • PTSD is an anxiety disorder impacting ~11.7M people with ~55% diagnosed • Approx. 65% of PTSD patients are treated with pharmacotherapy • Approx. 75% of patients on pharmacotherapy continue to experience sleep disturbance symptoms • Anxiety is one of the top 3 reasons for self-medication with cannabis • Early evidence for both THC and CBD in the treatment of PTSD • Nabiximols offers potential to reduce sleep disturbance symptoms, as well as anxiety and irritability

Sources: DiPiro. Spinal Cord. 2018; McGuire. Spasticity: Diagnosis and Management, 2011; Nicholson. Muscle Nerve. 2018; AANS Website; UpToDate; Physician Interviews; ClearView Analysis. Goldstein. Soc Psychiatry Psychiatr Epidemiol 2016; Kessler. Arch Gen Psychiatry. 2012; Kessler. Arch Gen Psychiatry. 2005; UpToDate; Physician Interviews; ClearView Analysis

May 2020 GW Pharmaceuticals Investor Presentation 22 GW’s Cannabinoid Platform: A Proprietary Growth Engine

PRE-CLINICAL PHASE 1 PHASE 2 PHASE 3 SUBMIT APPROVED EPIDIOLEX® (cannabidiol) Dravet syndrome Lennox-Gastaut syndrome Tuberous Sclerosis Complex Rett syndrome Nabiximols (marketed as Sativex® ex-US) MS spasticity Spinal Cord Injury spasticity PTSD Other neurological conditions CBDV Epilepsy Autism spectrum disorders OTHER Schizophrenia Neonatal hypoxic-ischemic encephalopathy

May 2020 GW Pharmaceuticals Investor Presentation 23 Key Financial Data

Q1 2020 net revenue $120.6m

Cash at March 31, 2020 $500.9m

FY 2020 R&D and SG&A expense guidance $530m–$560m

FY 2020 capital expense guidance $30m–$40m

Share Capital Current Options Fully Diluted ADS/m 31.2 1.4 32.6

May 2020 GW Pharmaceuticals Investor Presentation 24 2020 Key Priorities

Epidiolex® commercialization: Nabiximols in the US (known as “Sativex” ex-US): • Continue to drive revenue growth: • Commence pivotal clinical program in spasticity • Build on positive experiences from existing physicians associated with MS to increase prescribing to appropriate patients • Commence clinical program to expand future label to • Accelerate adoption across a broader prescriber base include spasticity associated with SCI • Continue partnerships with payers to expand access • Commence clinical program in PTSD • Enter long-term care segment • Obtain approval of TSC indication in both US and EU Additional pipeline: significantly expanding patient population • Commence Phase 2b study for the treatment of ® • Successful execution of EU launches of Epidyolex schizophrenia • Supplement existing Orange Book listed patents • Continue to explore CBDV in autism through a (expiry 2035) with additional use patents; progress combination of open-label and investigator-led RCTs “composition” patent application with data from one or more programs in 2020 • Advance medical literature for Epidiolex through top- • Execute NHIE clinical program tier journal publications and major scientific and medical meeting presentation

May 2020 GW Pharmaceuticals Investor Presentation 25 “Sound scientific research to investigate ingredients derived from marijuana can lead to important therapies. This new treatment provides new options for patients. Because of this careful, scientific and evidence-based evaluation by the FDA, health care providers can rely on having a quality product that delivers a consistent, uniform dose of an effective medication that is able to deliver a predictable treatment to patients.”

Former FDA Commissioner Scott Gottlieb, M.D. June 24, 2018

https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm611047.htm THANK YOU!

Poppy Living with Dravet syndrome

Stephen Schultz www.gwpharm.com VP Investor Relations [email protected] 401-500-6570 NASDAQ: GWPH