Top-Line Results from thePhase 2 Clinical Trial ofADX-629 in Chronic Cough DATA RELEASE June 27, 2023 Nasdaq: ALDX © Aldeyra Therapeutics, Inc. 2023

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The Phase 2 Clinical Trial of ADX-629 in Chronic Cough Demonstrated Statistically Significant Reduction in Cough Frequency vs. Placebo The primary endpoint of safety was met:ADX-629 was well tolerated with no identified safety concerns. Statistical significance was achieved for all assessed continuous cough reduction endpoints: awake cough frequency (P=0.01), the key secondary endpoint; the secondary endpoint of 24-hour cough frequency (P=0.001); and related post-hoc assessments of awake cough count (P=0.001) and 24-hour cough count (P=0.001). The results from the Phase 2 clinical trial in chronic cough are consistent with activity demonstrated in previously disclosed clinical trials of ADX-629, including Phase 2 clinical trials in psoriasis, asthma, and COVID-19, adding to a growing body of evidence supportive of the activity of ADX-629 in systemic diseases associated with inflammation. ADX-629 is an investigational drug candidate.

ADX-629, a First-in-Class Orally Administered RASP Modulator, Has Demonstrated Activity in Phase 2 Clinical Trials ADX-629 is an investigational drug candidate. P values are derived from mixed model for repeated measures analysis of placebo group comparison to 0 (no change). SEM = standard error of the mean. P values derived from mixed model for repeated measures analysis of comparison to 0 (no change). NIAID = National Institute of Allergy and Infectious Diseases. LOCF = Last Observation Carried Forward. P = 0.001 P = 0.0003 P = 0.0008 Allergic Inflammation: Asthma Infectious Disease: COVID-19 Autoimmune Disease: Psoriasis

SCREENING RANDOMIZATION TREATMENT PERIOD 1 WASHOUT TREATMENT PERIOD 2 FOLLOW-UP A Phase 2, Multicenter, Randomized-Sequence, Double-Blind, Placebo-Controlled, Crossover Clinical Trial to Evaluate the Safety and Efficacy of ADX-629 in Adults with Chronic Cough Up to 21 Days 14 Days 14 Days 14 Days Screening Randomization Placebo ADX-629300mg BID Placebo ADX-629300mg BID Follow-up Primary Endpoint Safety Key Secondary Endpoint Awake cough frequency Secondary Endpoints 24-hour cough frequency QoL questionnaires Clinical impression scales Key Enrollment Criteria Adults with refractory chronic cough for > 1 year that is unresponsive to treatment Awake cough frequency of ≥ 10 coughs/hour Cough severity score of ≥ 40 on visual analog scale Non-smoker Not taking ACE-Inhibitors or any cough-modulating drugs during trial Cough frequency is number of coughs divided by hours. ADX-629 is an investigational drug candidate. ACE = angiotensin converting enzyme. QoL = quality of life

ADX-629 to Placebo (n=26) Mean (SD) or % Placebo to ADX-629 (n=25) Mean (SD) or % Mean Age (years) 65.3 (9.5) 65.2 (7.1) BMI (kg/m2 ) 29.4 (9.5) 28.4 (4.7) Gender Male (19%), Female (81%) Male (16%), Female (84%) Awake Cough Frequency 51.8 (44.4) 44.7 (32.4) Chronic Cough History (years) 18.8 (15.7) 11.2 (9.2) Baseline Characteristics Were Similar Across Sequences ADX-629 is an investigational drug candidate. Awake cough frequency is number of coughs while awake divided by hours awake. BMI = body mass index; SD = standard deviation.

ADX-629 Was Well Tolerated and No Safety Signals Were Identified ADX-629 is an investigational drug candidate. Severity summary reflects treatment-emergent adverse events. Placebo (n=51) ADX-629 (n=51) Serious Adverse Events 0 0 Severe 0 0 Moderate 2 (3.9%) 4 (7.8%) Mild 8 (15.7%) 10 (19.6%) Caused Discontinuation 0 0 51 patients were enrolled, and all patients completed both treatment periods.

ADX-629 Achieved the Key Secondary Endpoint of Reduction inAwake Cough Frequency in the Phase 2 Chronic Cough Clinical Trial Key secondary endpoint of awake cough frequency reduction achieved Reduction of awake cough frequency (coughs per hour) following ADX-629 treatment statistically significantly superior (P=0.01) to that following treatment with placebo with placebo t Key secondary endpoint results consistent with statistically significant (P=0.001) reduction in total awake cough count in favor of ADX-629 over placebo LS means and P values derived from mixed effect model of repeated measures analysis that adjusted for baseline and prior treatment to account for carryover effect. Awake cough frequency is number of coughs while awake divided by hours awake. ADX-629 is an investigational drug candidate. SE = standard error; LS = least squares. KEY RESULTS

ADX-629 Achieved the Secondary Endpoint of Reduction in24-Hour Cough Frequency in the Phase 2 Chronic Cough Clinical Trial Secondary endpoint of 24-hour cough frequency reduction achieved Reduction of 24-hour cough frequency (coughs per hour) following ADX-629 treatment statistically significantly superior (P=0.001) to that following treatment with placebo with 24-hour cough frequency endpoint results consistent with statistically significant (P=0.001) reduction in total 24-hour cough count in favor of ADX-629 over placebo KEY RESULTS LS means and P values derived from mixed effect model of repeated measures analysis that adjusted for baseline and prior treatment to account for carryover effect. Twenty-four cough frequency is number of coughs over 24 hours divided by 24. ADX-629 is an investigational drug candidate. SE = standard error; LS = least squares.

Lipid Profiles Improved Following ADX-629 Treatment in the Phase 2 Chronic Cough Clinical Trial LS means and P values derived from mixed effect model of repeated measures analysis that adjusted for baseline and prior treatment to account for carryover effect. ADX-629 is an investigational drug candidate. SE = standard error; LDL = low-density lipoprotein cholesterol; HDL = high-density lipoprotein cholesterol; LS = least squares.

Lipid Profiles Improved Following ADX-629 Treatment in Previously Completed Phase 1 and Phase 2 Psoriasis Clinical Trials P values derived from mixed effect model of repeated measures analysis that adjusted for baseline. Phase 1 results derived from assessments following ingestion of a fatty meal. ADX-629 is an investigational drug candidate. SEM = standard error of measurement ; LDL = low-density lipoprotein cholesterol; HDL = high-density lipoprotein cholesterol; AUC = area under the curve. Psoriasis Phase 2 Clinical Trial P = 0.005 P = 0.036 P = 0.0004 HDL (mg/dL AUC) LDL/HDL ratio (AUC) FFA (mM AUC) Phase 1 Clinical Trial

†Regulatory review timelines are flexible and subject to change based on the regulator's workload and other potential review issues. ‡The timing of ongoing clinical trials depends, in part, on the availability of clinical research facilities and staffing, and the ability to recruit patients. *Investigator sponsored. Dry Eye Disease PDUFA date of November 23, 2023† Upcoming Planned Clinical Milestones Reproxalap Proliferative VitreoretinopathyType C meeting with FDA to discuss completion of clinical development planned for H2 2023 Retinitis PigmentosaPhase 2 clinical trial top-line results expected in June 2023‡ ADX-2191 Atopic Dermatitis (Part 1), Idiopathic Nephrotic Syndrome (Part 1), and Sjögren-Larsson Syndrome*Phase 2 clinical trial top-line results expected in H2 2023‡ Moderate Alcohol-Associated HepatitisInitiation of Phase 2 clinical trial expected in H2 2023‡ ADX-629