Menlo Therapeutics Inc. March 2019 Developing Serlopitant, a Once-Daily Oral NK1 Receptor Antagonist for Pruritus

Safe Harbor Statements Special Note Regarding Forward-Looking Statements This presentation contains forward-looking statements, including statements about our plans to develop and commercialize our product candidates, our planned clinical trials for serlopitant, the timing of the availability of data from our clinical trials, the timing of our planned regulatory filings, the timing of and our ability to obtain and maintain regulatory approvals for serlopitant and the clinical utility of serlopitant, alone and as compared to other treatment options, the duration of patent protection, and other statements regarding strategy, future operations and plans, as well as assumptions underlying such statements. These statements involve substantial known and unknown risks, uncertainties and other factors, some of which are outside of our control, that may cause our actual results, levels of activity, performance or achievements to be materially different from the information expressed or implied by these forward- looking statements, including risks related to the clinical drug development process, the regulatory approval process, our reliance on third parties, and our ability to defend our intellectual property. We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements we make. Additional information that could lead to material changes in our performance is contained in our filings with the U.S. Securities and Exchange Commission. The forward-looking statements in this presentation represent our views as of the date of this presentation. We anticipate that subsequent events and developments will cause our views to change. However, while we may elect to update these forward-looking statements at some point in the future, we have no current intention of doing so except to the extent required by applicable law. You should, therefore, not rely on these forward-looking statements as representing our views as of any date subsequent to the date of this presentation. Additional Information This presentation concerns a product that is under clinical investigation and which has not yet been approved for marketing by the U.S. Food and Drug Administration. It is currently limited by Federal law to investigational use, and no representation is made as to its safety or effectiveness for the purposes for which it is being investigated.

Menlo Investment Highlights Serlopitant Phase 3 Development in 2 Pruritus Indications + Pipeline Phase 3 prurigo nodularis Granted Breakthrough Therapy Designation by the FDA Phase 3 psoriasis Phase 2 chronic pruritus of unknown origin Success in Large, Placebo-controlled Phase 2 Pruritus Trials Hit primary endpoint in 3 of 4 large placebo-controlled Phase 2 trials In all 4 trials, at every time point, showed improvement in pruritus vs. placebo Large Market Opportunity in Pruritus PN: 300-600K patients in the U.S. with no approved therapy Psoriasis: 7.5M patients diagnosed in the U.S.; >90% experience pruritus Cash Runway into Q4 2020 ~$136M cash as of 12/31/18 Solid IP U.S. composition of matter to 2030, incl. extensions; methods of use to 2033 3

Serlopitant Pipeline and Upcoming Milestones Serlopitant is a highly selective small molecule inhibitor of NK1 Receptor, given once daily, as an oral tablet Indication Phase 1 Phase 2 Phase 3 2019 2020 Anticipated Milestones Prurigo Nodularis Complete enrollment File NDA 2 Phase 3 trials ongoing Psoriasis EOP2 Mtg Targeting to initiate Phase 3 program in 2019 Chronic Pruritus of Unknown Origin Complete enrollment Phase 2 initiated in January 2019 Trial Results Targeted initiation 4

Serlopitant Met Primary Endpoints in 3 of 4 Phase 2 Pruritus Trials and Demonstrated Improvement Over Placebo at Every Assessed Time Point Chronic Pruritus – TCP-101 Prurigo Nodularis – TCP-102 N=257 N=127 Avg Itch VAS Change from Baseline VAS % Change from Baseline -28.3% -34.1% -41.4% -42.5% p=0.001 * p=0.013 * Treatment Week Treatment Week Atopic Dermatitis – MTI-103 Psoriasis – MTI-109 N=484 N=203 33% 21% WI-NRS Change from Baseline WI-NRS 4-point Responder Rate p=0.028 * -2.01 -2.25 * p=0.17 -2.32 p=0.11 Treatment Week Treatment Week *Primary endpoint Placebo Serlopitant 0.25 mg Serlopitant 1 mg Serlopitant 5 mg 5

Phase 2 Pruritus Studies – Serlopitant 5mg Responder Rate Chronic Pruritus – TCP-101 Prurigo Nodularis – TCP-102 NRS 4-Point Responder Analysis (Baseline to Week 6) WI-NRS 4-Point Responder Analysis (Baseline to Week 8) p=0.011 p=0.05 N=53 N=52 N=39 N=43 Atopic Dermatitis – MTI-103 Psoriasis – MTI-109 WI-NRS 4-Point Responder Analysis (Baseline to Week 6) WI-NRS 4-Point Responder Analysis (Baseline to Week 8) p=0.17 p=0.028 * N=158 N=160 N=101 N=102 Placebo Serlopitant 5mg *Primary endpoint. 6

Consolidated Safety Summary of Serlopitant Evaluated in ~1,600 patients and shown to be well-tolerated, including in patients who received treatment up to one year Most commonly reported treatment emergent adverse events across completed Phase 2 trials were: N=670 N=1261 TEAE Placebo (%) Serlopitant (%) Urinary Tract Infection 2.5% 4.8% Nasopharyngitis 3.7% Diarrhea 3.4% 4.7% Headache 6.3% 4.4%

Serlopitant for Pruritus Associated with Prurigo Nodularis Granted Breakthrough Therapy Designation by the FDA Phase 3 Program Ongoing Targeting 2020 NDA Filing

Prurigo Nodularis Prurigo Nodularis (PN) A chronic intensely pruritic skin condition Scratching leads to nodules which lead to more itch No approved therapies in US or EU No effective treatment options Itch is the Primary Complaint Among 100% of PN Patients (1) Primary Complaint Secondary Complaint Image courtesy of Prof. Sonja Stander, University Munster (1) Company survey of 30 physicians who treat PN patients.

Attractive Commercial Opportunity in PN 300K – 600K patients in US (1) ~185K PN patients visit physicians each year (1) On therapy 2-6 months per year (1) 75% of PN patients are diagnosed by a dermatologist ~5K derms treat majority of PN patients Estimated 50 person field force could reach high-prescribing derms $900 – $2,400 per month(2) (1) Internal company estimates (2) Estimates based on company payer research and symptom relief analogs

Limited Treatment Options Frustrate Patients and Physicians Living with PN Diagnosis Treatment Management Constant itch is extremely bothersome and alters lifestyle Majority of patients diagnosed by dermatologists Treatments are not always effective and may have limitations such as side effects “Trial and error” - topical steroids - antihistamines - intralesional injections - phototherapy - cryotherapy Patients resign themselves to live with it Severe patients may visit physician regularly (every 3-6 months) “It can be frustrating...very limited options to treat patients with. And even the options that we have, sometimes don't help or help just a little bit. So, these patients you see on an ongoing basis.” —Dermatologist “Yes, I had some type of relief. But, then, it started again. Every time I'd have a little bit of relief, and then it seems like another trigger…” —PN Patient

PN Phase 2 Study: Data Consistent Across Multiple Endpoints VAS – Primary Endpoint NRS serlopitant serlopitant VAS - 40mm Responder Analysis (Baseline to Week 8) Average Itch VAS WI-NRS - 4 Point Responder Analysis (Baseline to Week 8) Worst Itch NRS Placebo Serlopitant Placebo Serlopitant p=0.002 p=0.05

Ongoing NULARIS Phase 3 Studies in Prurigo Nodularis MTI-105 (US) & MTI-106 (EU) N~280 per trial PN of ≥6 weeks Trial 1: ~50 sites in US Trial 2: ~50 sites in Europe Screening pruritus ≥7 on WI-NRS Excludes active pruritic skin disease Primary endpoint WI-NRS 4-point responder rate at Week 10 Serlopitant 5 mg Placebo 2-4 week screening 10-week treatment 3-5 week follow-up MTI-105 ~50% enrolled* MTI-106 >50% enrolled* Data expected H1 2020 *As of 2/22/19

Serlopitant for Pruritus Associated with Psoriasis Phase 3 Targeted for 2019

Psoriasis Psoriasis is a chronic inflammatory disease of multiple systems causing areas of thickened skin, itch and pain No cure; treatments aim to improve symptoms ~7.5M diagnosed in the U.S.(1) Itch is the Most Frequent Patient Complaint(2) Current Standard of Care Does not Target Itch for Majority of Patients Moderate-Severe Psoriasis(1) 59% not treated 9% biologics 13% oral systemic 17% topicals 25% Mod / Severe Psoriasis(3) 75% Mild Psoriasis Mild Psoriasis(4) 49% not treated 42% topicals only (1) Armstrong, Dermatol Ther 2016 (2) Quality of Life & Work Productivity Impairment among Psoriasis Patients: Findings from National Psoriasis Foundation Survey 2003–2011 (3) National Psoriasis Foundation (4) Armstrong, JAMA Derm 2013

Large Market Opportunity for Pruritus with Psoriasis ~7.5M diagnosed patients in the US (1) 74% with moderate to severe itch (2) (~5.5M) ~75% not well controlled with current therapy(2) (~4M) On therapy 4-8 months per year (3) ~100-150 person field force could target high- prescribing derms and PCPs $900 – $1,200 per month(3) (1) Armstrong, Dermatol Ther 2016 (2) Company market research (3) Internal company estimates

PSORIXA Phase 2 Study in Psoriasis – Data Announced Dec. 2018 MTI-109 N=204 Plaque-type PsO for ≥6 months, ≤10% BSA Pruritus ≥ 4 weeks WI-NRS ≥ 7 w/in 24 hours of initial screening Primary endpoint WI-NRS 4-point responder rate at Week 8 Serlopitant 5 mg Placebo 2-4-week screening 8-week treatment 2-week follow-up PsO = Psoriasis ClinicalTrials.gov ID: NCT03343639

WI-NRS 4-point Responder Rate WI-NRS Change from Baseline Psoriasis Phase 2 Study: Data Consistent Across Multiple Endpoints Primary Endpoint - WI-NRS 4-Point Responder Analysis (Baseline to Week 8) WI-NRS 4-Point Responder Analysis (Change from Baseline) 33% 21% p=0.028 WI-NRS 4-point Responder Rate p=0.028 * Secondary Endpoint: WI-NRS 4-Point Responder Analysis (Baseline to Week 4) WI-NRS (Change From Baseline) -2.02 WI-NRS Change from Baseline -2.77 p=0.039 * *Follow-up visit at Week 10. Treatment through Week 8 only. Placebo Serlopitant 5mg

Serlopitant for Chronic Pruritus of Unknown Origin (CPUO) Phase 2 Initiated in Q1 2019

Chronic Pruritus of Unknown Origin – A Large and Underserved Market CPUO Defined as pruritus lasting 6 weeks or longer, with no identified underlying disease Also referred to as idiopathic pruritus or pruritus of undetermined origin Overlaps with pruritus of the elderly / senile pruritus Large market 8-15%(1) of ~80M chronic pruritus patients(2) No approved therapies in US or EU In patients with severe pruritus that cannot be eliminated by identifying and treating an underlying cause…, topical therapy and lifestyle changes are unlikely to be sufficient, and systemic therapy should be considered. Given a paucity of data from randomized trials to evaluate various therapies, therapeutic choices are largely based on clinical experience and anecdotal reports. Sedating antihistamines are commonly used as first-line therapy but often have only modest efficacy…. Yosipovitch. NEJM. 2013 (1) Weisshaar, 2012 (2) Lifetime prevalence. Matterne, Acta Der Venereol, 2013

Post Hoc Analyses of Completed Phase 2 Studies with Serlopitant Support Phase 2 Study in Chronic Pruritus of Unknown Origin Observed patterns in three completed Phase 2 studies in pruritus suggest the following types of patients respond better to serlopitant: patients without inflammatory skin disease older patients patients with longer duration of pruritus TCP-101 Post-hoc Analysis Results Patients Without a Self-reported History of Inflammatory Skin Disease Patients with a Self-reported History of Inflammatory Skin Disease (1) NRS 4-point Responder Rate at Week 6 N=27 N=26 N=27 N=18 N=26 N=26 N=28 N=34 (1) Includes patients with a self-reported history of cutaneous lupus erythematosus, dermatitis, atopic dermatitis, contact dermatitis, dry skin, dyshidrotic eczema, eczema, asteatotic eczema, nummular eczema, hand dermatitis, keratosis pilaris, lichen planus, mechanical urticaria, neurodermatitis, photosensitivity reaction, psoriasis, rash, erythematous rash, pruritic rash, seborrheic dermatitis, stasis dermatitis, and urticaria.

Primary endpoint at week 10 Phase 2 Study in CPUO MTI-117 N~200 Chronic pruritus of unknown origin ≥6 months WI-NRS ≥7 prior to screening Primary endpoint WI-NRS 4-point responder rate at Week 10 Serlopitant 5 mg Placebo 2- or 4-week screening 10-week treatment Primary endpoint at week 10 3-week follow-up Data Expected mid-2020

Financial Information and Conclusion

Key Financial Highlights Quarter Ended December 31, 2018 Cash & investments $136M Operating expenses Including $1M non-cash stock-based compensation $18M Common shares outstanding 23M Forward-Looking Information (Provided Feb. 27, 2019) 2019 Estimated operating expenses Including ~$3M-$6M non-cash stock-based compensation $78M-$88M Estimated cash runway Into Q4 2020

Menlo Investment Highlights Serlopitant Phase 3 Development in 2 Pruritus Indications + Pipeline Phase 3 prurigo nodularis Granted Breakthrough Therapy Designation by the FDA Phase 3 psoriasis Phase 2 chronic pruritus of unknown origin Success in Large, Placebo-controlled Phase 2 Pruritus Trials Hit primary endpoint in 3 of 4 large placebo-controlled Phase 2 trials In all 4 trials, at every time point, showed improvement in pruritus vs. placebo Large Market Opportunity in Pruritus PN: 300-600K patients in the U.S. with no approved therapy Psoriasis: 7.5M patients diagnosed in the U.S.; >90% experience pruritus Cash Runway into Q4 2020 ~$136M cash as of 12/31/18 Solid IP U.S. composition of matter to 2030, incl. extensions; methods of use to 2033 25