Immune Thrombocytopenia (ITP) is a condition where the body doesn't have enough platelets, which help stop bleeding. This study is testing a medicine called rilzabrutinib for adults and teenagers with ITP. Some will get the real medicine, and others will get a fake pill called a placebo. The study lasts about 60 weeks, which includes a screening period, a treatment period, and follow-up visits. Some participants might continue with a long-term extension for up to 12 months.

• The study lasts up to 60 weeks, with multiple visits.
• Participants will either receive rilzabrutinib or a placebo.
• There's a chance for a longer extension of the study.

To be part of the study, participants need to have had ITP for a certain amount of time and must not have other medical conditions that could interfere with the study. Pregnant women, people with certain cancers, or those who've had specific recent treatments can't join. Participants must agree to follow study rules and attend all visits.