The study is divided into five periods: screening period, randomized period, open-label extension (OLE) period, long-term OLE period, and safety follow-up period. If you choose to join the study, you may participate in the following: Screening Period

This period includes 1 study visit to determine if you are a good candidate for the study.

The screening visit includes reviewing and signing a consent form, completing breathing tests, having a physical exam, getting an electrocardiogram, and having blood draws.

Randomized Period During this period of the study, you will get a random assignment to either:

• Take the study drug once or twice a day for 26 weeks; OR
• Take a placebo (inactive substance with no drug in it) once or twice a day for 26 weeks

You will have a 2-in-3 chance of getting the study drug and a 1-in-3 chance of getting the placebo during this period. This period will include visits to our clinic about every 2 weeks for the first 6 weeks, then about every 4 weeks for the next 20 weeks (8 visits altogether). Open-Label Extension (OLE) Period After the Randomized Period, you have the option to continue to the OLE period. During this period, everyone will take the study drug regardless of their assignment in the randomized period. This period also lasts for 26 weeks and you will visit our clinic about every 4 weeks during the OLE period (6 visits altogether). Long-Term OLE Period After the OLE period wraps up, you will have the option to continue to the long-term OLE. Everyone who chooses to participate in this period will continue to take the study drug. You will visit our clinic every 12 weeks during this period. This period will continue indefinitely and will end when the study drug is either approved by the FDA or the study"s sponsor and/or any governing agency decides to terminate the study for any reason. Safety Follow-Up Period Whenever you stop taking the study drug, we will schedule you to come to our clinic for a safety follow-up visit. This visit will be about 7 days after you take your last dose of the study drug. You will have a thorough physical exam and interview with the study team.