Pennsylvania employees do not have to tell their employers that they are medical marijuana users, but employers are not prohibited from asking. In most cases, they will not ask, but if they do, it is not advisable to be dishonest. Prospective employees who are applying for jobs with companies that are known to do drug testing might want to be up front and let them know. If the employee only uses the medical marijuana at home and does not think that the employer will conduct drug testing, it can remain a private matter.