This comment is specifically for those interested in Amtrak employment, as I don't have any personal firsthand experience in the hiring process at other railroads.
If you have any prescription drugs that affect your ability to perform the job description for which you are applying, you cannot be offered the position. You can appeal the descision of the Human Resources Department by applying through the Amtrak Medical Department and have an Amtrak Doctor or Surgeon provide you and the company a professional medical opinion of if taking a specific drug will effect your work performance and safety record on the worksite.
If you are currently an Amtrak employee and your condition changes due to being prescribed a drug that prevents you from performing your duties, you can seek an job assignment change or seek a "non-operations" position in your division that will provide for a safe work environment. These change of status requests are managed and determined by the Amtrak Medical Department and the employee is protected from termination or furlough through the collective bargaining agreement under the Operation Red Block admendments.