that will depend on your definition of "difficult"
there is physics, biology, anatomy, math, etc. i just graduated from the Baker College program and nobody flunked out or dropped due to the program being too hard. success in the program depends on being a good/motivated student and your interest in the subject/profession.
some schools may be harder than others depending on how they are set up, how many classes per quarter, etc. if your serious about going into the field check our several programs. Beaumont hospital, Sinai Grace, Henry Ford Community College, and Baker College all have accredited programs.
Be sure the program results in at least an Associates Degree and is accredited by JCERT.
each program is set up differently and each has its ups and downs. check them out and see which fits your learning style and career goals.