A Phase 1 Study to Evaluate the Safety and Pharmacokinetics of ABBV-243 in Healthy Adults.

Inclusion Criteria:

• Individuals between 18 and 60 years of age inclusive at the time of Screening.

• BMI is ≥ 18.0 to ≤ 32.0 kg/m2 after rounding to the tenth's decimal at Screening.BMI is calculated as weight in kg divided by the square of height measured inmeters.

• Females, Non-Childbearing Potential are eligible as defined by meeting the followingcriteria:

• Permanent sterility due to a hysterectomy, bilateral salpingectomy, orbilateral oophorectomy.

• Non-surgical permanent infertility due to Mullerian agenesis, androgeninsensitivity, or gonadal dysgenesis; investigator discretion should be appliedto determining study entry.

• Postmenopausal female who is age ≤ 55 years with no menses for 12 or moremonths without an alternative medical cause AND an FSH level ≥ 30 IU/L.

• Postmenopausal female who is age > 55 years with no menses for 12 or moremonths without an alternative medical cause.

• Females, Childbearing Potential are defined as all other females who do not meet theabove criteria and must adhere to the following:

• Must not be pregnant or breastfeeding.

• Must agree to avoid pregnancy while taking study treatment(s) and for at least 200 days after the last dose of study treatment.

• Must agree to use a contraceptive method listed below (as per localregulations) that is highly effective (with a failure rate of < 1% per year,when used consistently and correctly). Participants must provide documentationto the site.

• Bilateral tubal occlusion/ligation.

• Intrauterine device (IUD) to be inserted at least 30 days prior to Screening.

• Intrauterine hormone-releasing system (IUS) to be inserted at least 30 daysprior to Screening.

• Part 2 only:

Healthy Japanese and Han Chinese male or female; between 18 and 60 years of age, inclusive at the time of Screening.

• Han Chinese participants must be first- or second-generation Han Chinese of full Chinese parentage. First-generation participants are defined as those born in China to two parents and four grandparents also born in China of full Chinese descent. Second-generation participants are defined as those born outside of China to two parents and four grandparents born in China of full Chinese descent.

OR

• Japanese participants must be first- or second-generation Japanese of full Japanese parentage. First-generation participants will have been born in Japan to two parents and four grandparents also born in Japan of full Japanese descent. Second-generation subjects born outside of Japan must have two parents and four grandparents born in Japan of full Japanese descent.

Exclusion Criteria:

• History: of epilepsy, any clinically significant cardiovascular, respiratory (exceptmild asthma as a child), renal, endocrine, hepatic, gastrointestinal, hematologic orpsychiatric disease or disorder, or any uncontrolled medical illness.

• History of any clinically significant sensitivity or allergy to any medication orfood.

• Evidence of dysplasia or history of malignancy (including lymphoma and leukemia)other than successfully treated non-metastatic cutaneous squamous cell, basal cellcarcinoma, or localized carcinoma in situ of the cervix.

• History or evidence of active Tuberculosis (TB) disease or latent TB infection.