This clinical trial is focused on studying a condition known as Hereditary Angioedema, which is a rare genetic disorder that causes sudden swelling in various parts of the body, such as the face, hands, and feet. The study is testing a new treatment called Deucrictibant (PHA-022121), which is taken as a soft capsule by mouth. The purpose of the study is to see how effective Deucrictibant is in providing relief from the symptoms of Hereditary Angioedema attacks compared to a placebo.

Participants in the study will be randomly assigned to receive either the Deucrictibant capsule or a placebo during different periods of the study. This is known as a crossover study, meaning that each participant will have the chance to receive both the actual medication and the placebo at different times. The study will last for a period of up to 42 days, during which participants will take the medication as needed when they experience an attack. The researchers will monitor how quickly and effectively the medication provides relief from symptoms.

The study aims to gather information on how well Deucrictibant works in reducing the time it takes for symptoms to improve during an attack. This information will help determine if Deucrictibant can be a reliable on-demand treatment option for people with Hereditary Angioedema. Participants will be asked to record their symptoms and any changes they experience using an electronic diary, which will help the researchers assess the effectiveness of the treatment.