The purpose of this study is to assess the efficacy and safety of oral administration of orismilast for treatment of mild, moderate, or severe hidradenitis suppurativa (HS) in adults.

Inclusion Criteria:

1. Male or female adult patients, 18 years of age or older.
2. Have mild to severe HS for at least 1 year prior to the baseline visit, as determined by the investigator through participant interview and/or review of the medical history.
3. Have HS lesions in at least 2 distinct anatomic area (right/left axillary, inguinal, inframammary, abdominal, perineal).
4. Has a total inflammatory lesions (AN) count of greater than or equal to 2.
5. Total draining fistula count of less than or equal to 30.
6. A stable analgesic dose for 2 weeks prior to baseline.

Exclusion Criteria:

1. Presence of active skin lesions other than HS that could interfere with the assessment of HS.
2. Receipt of prescription topical therapies for HS within 7 days prior to the baseline visit (Visit 2).
3. Receipt of systemic therapies for HS, within 28 days prior to the baseline visit.
4. Any oral antibiotic within 28 days prior to baseline visit.
5. Receipt of a live vaccine within 14 days prior to screening.
6. Biologic use for indications other than HS within a minimum of 30 days or 5 half-lives of the drug, whichever is longer, prior to baseline.
7. Treatment with any investigational drug of chemical or biologic nature within a minimum of 30 days or 5 half-lives of the drug, whichever is longer, prior to baseline.