The goal of this clinical trial is to learn if a new trientine tetrahydrochloride (TETA 4HCl) formulation administered once a day compared to d-Penicillamine (DPA) as a first line treatment for people living with Wilson's disease (WD) is effective and safe. The study is enrolling children aged 8 years and older weighing at least 55 lb (25 kg) and adults with a recent diagnosis of WD. People recently diagnosed with WD, may be eligible for the study if they have either not started copper chelating treatment (such as DPA or trientine) or have been taking zinc salts for less than 28 days. Participants will be randomly allocated (like tossing a coin) to receive either DPA or TETA 4HCL for 48 weeks. During this time period participants will have up to 12 visits for health checks and assessments including blood and urine testing. In addition, at some visits participants may be asked to complete questionnaires on treatment satisfaction, and overall well-being.