If any of those medications have side effects that could have serious or injurious consequences at work, such as causing you to pass out, have balance or motor issues, affect your behavior, etc., then the employer does likely have a right to know: the employer has the right to protect itself from liability, for injury to yourself or others, so it has the right to know if you are taking medication that could cause injury to you or others, and/or damage to its equipment or property.