Controlled substances and precursor chemicals

DEFINITION: Controlled substances are drugs that are regulated by the United States (US) Controlled Substances Act and by state laws. The laws aim to prevent the trafficking of illegal drugs and to minimize the danger of abuse and addiction to drugs that have valid medical uses. Precursor chemicals are used in the manufacture of controlled substances.

Controlled Substances and the Law

The Controlled Substances Act (part of the Comprehensive Drug Abuse Prevention and Control Act of 1970) consists of many laws regulating the manufacture and distribution of substances that are illegal or that can become addictive or abusive. The term substance is used in the act rather than the term drug because substance is a more encompassing term.

Substances listed in the act are classified into five schedules. Schedule I substances have a high potential for abuse and have no accepted medical use. They are, therefore, illegal drugs and cannot be sold or used; violators of Schedule I are prosecuted.

Schedules II through V substances have acceptable medicinal uses and are progressively less likely to be misused or to cause physical or psychological dependence. The rules for prescribing and dispensing controlled drugs by physicians and pharmacists are most rigorous for Schedule I drugs, and they are progressively less rigorous for Schedule II to V substances.

Physicians must be registered with the US Drug Enforcement Administration to prescribe controlled substances, and they must maintain detailed records of all transactions. The number of authorized refills (if any) must be stated and adhered to. The act has been modified several times since its enactment in 1970, and the classification of specific substances is subject to change.

Controlled Substances Act: Schedule Characteristics

Schedule I includes numerous substances classified as opioid drugs and hallucinogens, as well as a few depressants and stimulants. Opioid drugs have a chemical structure and physiological activity similar to opium, which is derived from the poppy plant. Opioid drugs are also known as narcotic drugs or narcotics.

Opioid drugs such as heroin and several morphine and codeine drugs are useful in treating moderate to severe pain. Still, these drugs are listed in Schedule I because of their potential for abuse and dependence.

Hallucinogens include the synthetic compound LSD (lysergic acid diethylamide) and also peyote and mescaline, which are found naturally in certain cacti. Marijuana is a popular drug with a controversial classification. Although around forty states had legalized medical marijuana by the mid-2020s, and twenty-four legalized recreational marijuana, it remained a Schedule I substance under federal law. Authorities reviewed federal policy on cannabis several times, but marijuana remained federally illegal in subsequent years. In May 2024, the Drug Enforcement Administration (DEA) proposed a change that would reschedule marijuana from a Schedule I to a Schedule III substance; however, this change was the subject of numerous delays, stretching the discussion through 2025.

Schedule II drugs include the opium poppy and the purified opium derived from the poppy. Other opioid drugs in Schedule II include cocaine, methadone, oxycodone, hydrocodone, hydromorphone, and natural coca leaves. Oxycodone, sold under the trade name OxyContin, is a valuable drug for relieving chronic pain, but the drug has become widely popular with abusers. The opioid crisis of the early twenty-first century exhibited the dangers of Schedule II drugs.

Included in Schedule II are the amphetamines, which act as stimulants. Methamphetamine is a synthetic compound made from amphetamine. Short-acting barbiturates are also in this schedule.

Schedule III substances include anabolic steroids, some stimulants, and depressants. Drugs that have a depressant effect on the central nervous system act as sedatives. Intermediate-acting barbiturates are included in this category. Drugs that have a stimulant effect on the central nervous system include amphetamines, which are not listed as Schedule II. Also included are drug formulations or preparations that have a limited quantity of narcotics.

Schedule IV drugs act as central nervous system depressants and produce sedation, induce sleep, and reduce anxiety. The most common drugs in this group are other barbiturates, including barbital, phenobarbital, and methylphenobarbital. Also included in this schedule are other drugs that have a similar effect, such as chloral betaine, meprobamate, and ethchlorvynol.

Schedule V drugs include formulations containing limited quantities of narcotic drugs in combination with other medically active drugs. The levels of narcotic drugs allowed are less than those in Schedule III.

Many prescription drugs are controlled substances, and the diversion of these drugs for nonmedical uses is increasing rapidly. Opioids are by far the most common prescription drugs that are diverted to illicit uses. Some professionals in the medical community believe pain is actually undertreated. This belief is controversial because increased prescriptions for opioid drugs increase the supply for diverted uses. The overall effectiveness of opioids for pain relief remains a topic of debate.

The diversion of prescription drugs can occur when persons sell or give their drugs to friends or associates. Diversion can also occur by theft or by what is called doctor shopping, visiting several doctors to obtain multiple prescriptions. The White House Office of National Drug Control Policy, established in 1989, addresses problems in illicit drug supply and use and coordinates efforts to control the problem.

Precursor Chemicals

Precursor chemicals are chemicals used in the synthesis and manufacture of controlled substances. They become part of the drug’s chemical structure. It is difficult to regulate these precursor chemicals because they also have valid commercial uses.

Also of concern to drug enforcement officials are essential chemicals. These chemicals are used to extract, purify, and concentrate drugs from natural sources. Essential chemicals do not become part of the molecular structure of a drug. Methamphetamine precursors such as pseudoephedrine, phenylpropanolamine, and ephedrine are most problematic.

The US Chemical Diversion and Trafficking Act (1988), which amended the Controlled Substances Act of 1970, regulates forty chemicals as List I and List II chemicals in the US Code of Federal Regulations. In addition to administering regulatory controls, the act administers criminal sanctions that control the diversion of precursor chemicals; however, it permits access to chemicals necessary for legitimate commerce.

Bibliography

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Manchikanti, Laxmaiah. "National Drug Control Policy and Prescription Drug Abuse: Facts and Fallacies." Pain Physician, vol. 10, 2007, pp. 399–424.

"Overview of Controlled Substances and Precursor Chemicals." USC Environmental Health and Safety, ehs.usc.edu/research/cspc/chemicals. Accessed 10 Dec. 2025.

"Precursor Chemicals." HPRA, www.hpra.ie/homepage/controlled-substances/precursor-chemicals. Accessed 10 Dec. 2025.