Working in the healthcare industry means you are in contact with vulnerable people, children, pharmaceutical drugs, drug-related equipment, confidential information, and other areas of sensitivity. If you have a criminal record or a history of drug use, you must disclose this.
If you do not have either, assure the interviewer that you can pass a complete background check and drug test without any issues. If you have a criminal record, you can say something like: 'I have a misdemeanor on my record from 15 years ago. I am happy to continue the interview process and comply with your background checks if you allow for some exceptions.' Even if you live in an area that allows the use of medical marijuana, most healthcare agencies will not allow employees to use this substance due to the nature of the industry and the patients you will be in contact with. If you use medical marijuana, investigate the policies of the agency you are interviewing with before applying for a job so you are not disqualified after taking the drug test.