Hidradenitis suppurativa (HS) is a skin condition causing painful lumps in areas like the underarms and groin. This study tests a medicine called upadacitinib to see if it helps people with moderate to severe HS who did not get better with another treatment called anti-TNF therapy. TNF stands for tumor necrosis factor, a substance in the body that can cause inflammation.

In this study, participants will take upadacitinib or a placebo (a pill with no medicine). The study is "double-blinded," which means neither the participants nor the doctors know who is getting the real medicine. The study has three parts and lasts for about two years and two months. Around 1328 people will be part of this study at 275 locations worldwide.

During the study, participants will take pills once a day and go to regular doctor visits to check how well the treatment is working and if there are any side effects.

• Participation includes taking daily pills and attending regular outpatient visits for over two years.
• Participants will be randomly assigned to receive either upadacitinib or placebo, with a 50% chance for each.
• This study might be more demanding than usual care because of the frequent visits and assessments.