Currently, the minimum requirement to be an occupational therapist is a master's degree, however, there are programs that offer an entry-level doctorate degrees. That means that the minimum time is either six or seven years as a minimum. However, most students take a total of seven or eight years as they work to complete the pre-requisite courses. You can find a list of accredited programs here at the American Occupational Therapy Association website.
Of note, the profession of occupational therapy also utilizes "COTAs" who assist the occupational therapist in providing care. They typically undergo 2-3 years of school. You can learn more about OT/COTAs here
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