 This is a randomized the study medication is assigned by chance, double-blind neither physician nor participant knows the identity of the assigned treatment, placebo-controlled one of the study medications is inactive, multicenter, parallel group study each participant group receives different treatments simultaneously. Participants will be randomly assigned in a 1:1:1 ratio to receive either ustekinumab 45 mg, ustekinumab 90 mg, or placebo. The study will consist of a screening period, a 12-week double-blind treatment period, and a 12-week follow-up period. During the double-blind treatment period, participants will receive one subcutaneous injection of study medication at Week 0 and Week 4. Participants will return to the study center for 7 evaluation visits on Weeks 2, 4, 8, 12, 16, 20, and 24. Clinical response will be evaluated by Eczema Area and Severity Index EASI, Investigators Global Assessment IGA, photography, and Dermatology Life Quality Index DLQI. Participants will record their itch condition twice daily using the participant daily diary from 2 weeks prior to randomization until Week 12. Blood samples will be drawn at time periods during the screening, double-blind treatment, and follow-up periods. Participant safety will be monitored throughout the study. Participants are permitted to use concomitant topical medications, as defined in the protocol and without any increase in dose, from 4 weeks prior to randomization through to the end of the treatment period. After Week 12, additional treatment can be started or the dose of concomitant medications can be increased, if no improvement in clinical response is observed; in these cases EASI, IGA, and photography evaluations will be stopped. The study duration for each participant is expected to be approximately 30 weeks. Ustekinumab also known as STELARA is an antibody medication that inhibits the inflammatory proteins IL-12 and IL-23 and is approved as a treatment for moderate to severe plaque-type psoriasis; this study will examine whether ustekinumab can provide benefit in atopic dermatitis and assess for any risks or side effects. 