Adjunct university or community college instructors/professors have to be "academically" or "professionally" qualified. This varies depending on the accreditor's requirements* and, occasionally, the state where the school is located (e.g. California and Oregon may have distinct requirements). You can look at a school's website to find their accreditor and the accreditor's website to find the requirements.
Academically qualified means the degree attained by the instructor. Professionally qualified means the on-the-job experience. Someone with a PhD in bio is academically qualified to teach bio. Bill Gates is professionally qualified to teach computer science, or entrepreneurship even though he didn't obtain a BA/BS. Professionally qualified is subjective.
Generally, someone with a BA/BS can teach community college general education (say office skills, excel and powerpoint), someone with a Masters can teach BA/BS classes and someone with a PhD can teach Masters or BA/BS. But if someone is professionally qualified they can teach up a level. For example, I have a masters but teach masters-level students because I have specialized training in finance.
With an MD, you might be considered by some schools and accreditors to be equivalent to a PhD (for approval to teach, not for tenure or a permanent full-time position). It just depends. You'd likely be qualified to teach bio or chem if your undergrad degree is in bio or chem but not if your undergrad degree is in economics, for example.
Best idea is to reach out to any professors or deans that you know at local colleges. That's how I got my first college teaching job.
You can also try the Chronicle of Higher Education which has a huge job search engine and you can have new jobs emailed to you based on criteria that you select.
Good luck!
*Accreditors include:
- Middle States Commission on Higher Education (MSCHE)
- New England Association of Schools and Colleges (NEASC CIHE)
- New England Association of Schools and Colleges (NEASC CTCI)
- North Central Association Commission on Accreditation and School Improvement (NCA CASI)