Can my employer or potential employer share my drug test results with anyone other than myself?

The answer depends on who the employer is telling about your drug test results.  If he is telling co-workers, then most definitely not.  The short answer is that the information should only be shared with those who have a medical or strong need to know.  Also depends on what is being said.  The rules may be a little looser if some such as a boss or HR person is told only that you failed at test.  Telling people what drug may have shown up would be a potential violation.  Speak to any attorney in your area for more details