There are no laws to protect you from accurate and true references. You can pursue a lawsuit if you are defamed, meaning untrue things were said that affect your professional reputation. You can sue in small claims court where you do not need a lawyer. The previous employer carries a level of responsibility to inform future employers if there were true, serious issues with performance. If concerned, there are companies who will do a reference check for you for fee to see what the former employer is saying.
As you pursue your career, a smart approach is to collect LETTERS of RECOMMENDATION from anyone in a position to know your work. If you are a student, or recent graduate, request ones from teachers. Before you leave a job, request one from supervisors, managers, committee chairs, physicians, etc. If you know someone prominent in the community who can attest to your character, request a letter.
Also save throughout your career, any PERFORMANCE EVALUATIONS you receive. You have a right to a copy of any form you sign. If you receive a poor evaluation, request guidance on how you can improve.
Most MED ERRORS occur not due to one person's actions but due to poor design of a process and the affect of many person's actions. The last person in line for the error is usually blamed. Study JCAHO's recommendations and ismp.com "lessons learned" for how to prevent med errors. Search any patient safety website for information on med error prevention. When re-employed, ask to be on the medication committee. You have the experience and the motivation to be a contributor who can make a difference.
If unable to gain employment, consider volunteering or taking a low-stress part time healthcare job to rebuild your resume, such as wellness tasks in LTC, nutrition programs or flu vaccine clinics. When you perform well, ask for a letter or give them a self made check-sheet to rate your performance that they can sign and date.
If a prospective employer asks you to explain, keep your answer short and honest. Truth has a ring to it and someone, somewhere will appreciate it.
Good luck and never stop caring to give your best.