Of particular concern with Internet pharmacies is the ease with which people, youth in particular, can obtain controlled substances (e.g., Vicodin, generically known as hydrocodone) via the Internet without a prescription issued by a doctor/practitioner who has an established doctor-patient relationship. There are instances where a practitioner issues a prescription, brokered by an Internet server, for a controlled substance to a "patient" s/he has never met. In the United States, in order for a prescription for a controlled substance to be valid, it must be issued for a legitimate medical purpose by a licensed practitioner acting in the course of legitimate doctor-patient relationship. The filling pharmacy has a corresponding responsibility to ensure that the prescription is valid. Often, individual state laws outline what defines a valid patient-doctor relationship. The Food and Drug Administration (FDA) is also heavily involved in monitoring internet pharmacies and has issued warnings against several companies who have violated the U.S. Federal Food, Drug, and Cosmetic Act that protects individuals against rogue online pharmacies.