BELLUS Health : Presentation BELLUS RELIEF Phase 2 Trial Topline Results

BLU-5937:

RELIEF Phase 2 Topline Data

July 6, 2020

Forward Looking Statements

Certain statements contained in this presentation, other than statements of fact that are independently verifiable at the date hereof, may constitute "forward-looking statements" within the meaning of Canadian securities legislation and regulations, the U.S. Private Securities Litigation Reform Act of 1995, as amended, and other applicable securities laws. Forward-looking statements are frequently, but not always, identified by words such as "expects," "anticipates," "believes," "intends," "estimates," "potential," "possible," "projects," "plans," and similar expressions. Such statements, based as they are on the current expectations of management, inherently involve numerous important risks, uncertainties and assumptions, known and unknown, many of which are beyond BELLUS Health's control. Such statements include, but are not limited to, the potential of BLU-5937 to successfully treat chronic cough, chronic pruritus and other hypersensitization-related disorders, BELLUS Health's expectations related to its preclinical studies and clinical trials, including its clinical development plan, timing and design of future clinical trials, expected approval requirements and timing for regulatory interactions for its chronic cough program and its chronic pruritus program, the potential tolerability profile, P2X3 selectivity, drug characteristics and other characteristics of BLU-5937 as compared to other competitor candidates and the potential applicability of BLU-5937 and BELLUS Health's P2X3 platform to treat other disorders. Risk factors that may affect BELLUS Health's future results include but are not limited to: the ability to expand and develop its project pipeline, the ability to obtain adequate financing, the ability of BELLUS Health to maintain its rights to intellectual property and obtain adequate protection of future products through such intellectual property, the impact of general economic conditions, general conditions in the pharmaceutical industry, the impact of the COVID-19 pandemic on BELLUS Health's operations, plans and prospects, including to the initiation and completion of clinical trials in a timely manner or at all, changes in the regulatory environment in the jurisdictions in which BELLUS Health does business, stock market volatility, fluctuations in costs, changes to the competitive environment, achievement of forecasted burn rate, potential payments/outcomes in relation to indemnity agreements and contingent value rights , achievement of forecasted preclinical study and clinical trial milestones, reliance on third parties to conduct preclinical studies and clinical trials for BLU-5937 and that actual results may vary once the final and quality-controlled verification of data and analyses has been completed. In addition, the length of BELLUS Health's product candidate's development process and its market size and commercial value are dependent upon a number of factors. Moreover, BELLUS Health's growth and future prospects are mainly dependent on the successful development, patient tolerability, regulatory approval, commercialization and market acceptance of its product candidate BLU-5937 and other products. Consequently, actual future results and events may differ materially from the anticipated results and events expressed in the forward-looking statements. BELLUS Health believes that expectations represented by forward-looking statements are reasonable, yet there can be no assurance that such expectations will prove to be correct. The reader should not place undue reliance, if any, on any forward-looking statements included in this presentation. These forward-looking statements speak only as of the date made, and BELLUS Health is under no obligation and disavows any intention to update publicly or revise such statements as a result of any new information, future event, circumstances or otherwise, unless required by applicable legislation or regulation.

Please see BELLUS Health's public filings with the Canadian securities regulatory authorities, including, but not limited to, its Annual Information Form, and the United States

Securities and Exchange Commission, including, but not limited to, its Annual Report on Form 40-F, for further risk factors that might affect BELLUS Health and its business.

BLU-5937: Clear Path Forward from Phase 2 RELIEF Trial Results

Missed primary endpoint but achieved clinically significant and highly statistically significant reduction in cough frequency in pre-specified subgroup of high cough count patients

• • RELIEF trial did not achieve primary endpoint of reduction in awake cough frequency at any dose

• •In a pre-specified subgroup analysis of high cough count patients1, highly statistically significant and clinically meaningful reductions in awake cough frequency were achieved at all doses:

  • • 28-32% placebo-adjusted reduction in awake cough frequency (p<0.0015)

• • Well tolerated including low taste side effects at all doses; safety profile comparable to placebo

  • • 6.5-10% taste side effect across doses (4.9% on placebo); mostly mild

• •Clear path forward:

  • • Therapeutic dose range identified

  • • Patient population enrichment strategy

  • • Adaptive Phase 2b expected to start in Q4 2020

1Pre-specified sub-group analysis in patients ≥ median baseline awake cough count (32 coughs per hour; n=31)

RELIEF Phase 2 Results

Phase 2 RELIEF Study Trial Design

(A Randomized, Double-blind, Placebo-Controlled, Crossover, Dose Escalation Study of BLU-5937 in Subjects with Unexplained or Refractory Chronic Cough)

Primary endpoint:

Placebo-adjusted reduction in awake cough frequency using cough recorder

16 sites in UK and US:

40 patients from 8 UK sites

28 patients from 8 US sites

68 refractory chronic cough patients:

52 completed dosing

13 pandemic-related discontinuations

3 non-drug related discontinuations

4 dose levels:

25/50/100/200mg BID with forced dose escalation at 4-day intervals

Cough Recording Conducted