Controlled substances are drugs and other materials whose possession and use the federal government has chosen to regulate. Possession of a controlled substance isn't necessarily a crime; for many substances, it's legal to possess and use them when done under certain circumstances, such as under a doctor's supervision or during scientific research. Possession and use become illegal, however, when no legal justification applies; or when the substance (such as heroin) has absolutely no legitimate use.

     To learn about controlled substance laws in your state, jump ahead to the section on state-controlled substance laws by state.

What Are Controlled Substances?

     The federal government lists the various types of drugs that they consider to be "controlled," that is, available (if at all) only through a valid prescription or other legitimate avenue. The federal scheme, contained in the Controlled Substances Act (21 U.S.C.A. Sections 801 and following), lists five "schedules" of drugs, with the most dangerous substances in Schedule I, and the least in Schedule V. This classification applies in federal drug cases, and many states have adopted the federal schedule.

     To see the five schedules in the federal law, consult Section 812 of the Controlled Substances Act. For information on how your state classifies drugs, refer to the state-specific article listed below.

What is Illegal Possession of a Controlled Substance?

     Illegal possession of a controlled substance occurs whenever a person owns or otherwise possesses a drug or other controlled substance, without justification or permission. These charges usually apply when a person is found carrying marijuana, cocaine, methamphetamine, or other narcotics. It's important to note that some legally available drugs, such as prescription medications, qualify as controlled substances, and possession charges are possible when the person possessing the medication does not have a proper prescription.

     To convict someone of illegal possession of a controlled substance, the prosecutor must prove the following "elements" of the crime:

Knowing. The crime of possessing a controlled substance occurs whenever a person knowingly and intentionally has control of a controlled drug. However, the prosecution doesn't have to show that the accused knew that the drugs were controlled and that possession in this circumstance was illegal. Prosecutors only have to show that the accused knew the drugs were present and intended to use or control them. Prosecutors can show this from the circumstances of the case, and they do not need to have actual statements from the accused or evidence that the accused actually used the drugs.

     Possession means that a person has personal and physical control over the illegal substance. Courts have held that a person can have either actual or constructive possession over the drug. This means that a person actually has it in a pocket or otherwise in personal custody, or that the person has control over the drug, such as by having the drugs in a car's glove compartment, a bag, or hidden in the home.

Shared possession. A defendant can be convicted of possessing a controlled substance if the prosecutor can show the accused had at least partial control over the drug. For example, two roommates may each be convicted of possession if they shared an apartment in which the police found marijuana. However, prosecutors must show more than that the two were merely roommates in the same home, by proving, for example, that each defendant had control over the drugs or made incriminating statements about them.