Determining the applications and legal statuses for various drugs can be difficult, requiring the understanding of potential benefits and risks for each available drug. This is why many countries have developed classification systems to categorize various types of, and uses for, pharmaceutical and recreational drugs.

When classifying drugs, it is common to use multilevel systems that divide drugs into different categories. The United States uses a five-level system to categorize various drugs for medical use and legal control. In the case of dangerous or illegal substances, these systems provide additional guidance to limit usage and adverse reactions.

Understanding the severity of a drug’s side effects is crucial in identifying its use. Stronger drugs are listed in levels with more regulatory control and limited legal use. Beneficial drugs with limited negative effects tend to be listed toward the lower levels, where use is more common and less regulated. Those drugs in the middle of the classification system are generally drugs that see more widespread use despite potential negative effects because of their benefits.

Many drugs became popular as prescribed pharmaceutical medications and other medical applications because of their balance of effectiveness, potency, and potential side effects. Without drug classification systems that incorporate levels of acceptable risk, many of the most widely prescribed pharmaceutical medications may not be in use today.

Drug Classifications in the United States

According to PubMed Health, drugs are classified by commonalities, such as their use, ingredient lists, and chemical structures. In the United States, the Drug Enforcement Agency is largely responsible for enforcing drug-related laws and maintaining the list of controlled substances. Law enforcement officials, doctors, and pharmacists use the Drug Enforcement Agency’s drug classification list as a guide for enforcing legal guidelines.

The controlled substance list published by the Drug Enforcement Agency contains five different classifications of drugs. These classifications, referred to as schedules, range from illegal and more dangerous drugs to safer drugs that many people use on a daily basis to manage chronic health conditions and minor pain.

Schedule I

Schedule I consists of the most serious drugs and controlled substances that are not currently used for any medical purposes. These drugs often cause severe side effects and are prone to abuse and addiction. The drugs included in Schedule I represent the longest part of the controlled substances list.

Many of the drugs contained in Schedule I are widely unknown by the general public. Some of the drugs are used in the manufacturing of other products. These drugs are kept under strict control by manufacturers and law enforcement agencies, as they pose serious health risks to the general public. It is not common to come in direct contact with any of these drugs at pharmacies, drug stores, or within a hospital setting, as they are highly controlled and, in many cases, illegal.

Schedule I contains some of the most well-known recreational drugs subjected to restricted use around the world. Government agencies have banned many of these drugs due to misuse or dangerous side effects; however, many still proliferate via the illegal drug trade

Schedule I drugs include the following:

  • Morpheridine: This is a drug that used to be common as an analgesic. It was an ingredient found in related pain-relieving drugs and products. It is no longer used, as it was replaced by more effective options with less serious side effects. It has similar side effects to opioid pain relievers, such as decreased respiratory rates and other sedative–like properties. Morpheridine is banned in multiple countries around the world.
  • Peyote: Peyote, as a drug, is derived from the small cactus plant with the same name. This drug has intense psychoactive properties. While it has and continues to be used around the world in religious practices, it is banned from use recreationally and in pharmaceutical medications in the US. This is primarily due to its ability to alter perception. Long-term exposure may cause serious issues with brain function.
  • Heroin: According to the National Institute on Drug Abuse, heroin is a painkiller derived from the Asian opium plant. It is still used as a painkiller in some countries due to its high level of efficacy, and it is found in some cough medicines due to its strong effects on the respiratory system. Heroin is no longer used in most medical applications in the United States because of the nature of its potential side effects that include addiction and overdose.
  • Morphine: An opiate painkiller, morphine continues to be used in several medical applications due to its strength as a painkiller. However, it is used as a last resort after lesser painkillers have proven ineffective, and it is rarely used legally outside of a hospital setting. It is administered in the smallest possible dose to minimize potential side effects.
  • Marijuana: Despite its Schedule I status, marijuana is beginning to be used in legal medical applications in several states. It is, however, still an illegal drug in many states. According to Stanford University, marijuana’s classification as a Schedule I drug is questioned because of the medical benefits it potentially offers. In some states, such as California, marijuana dispensaries legally distribute marijuana to eligible patients. According to the Journal of Global Drug Policy and Practice, the marijuana available from dispensaries does not undergo testing and regulation like other legal medications. Many entities recommended this testing and supervision are put into place to ensure purity and quality of the drug.

Schedule II

Schedule II contains many medications that remain medically useful despite potential side effects. Some of the drugs in Schedule II are found in moderate amounts in various medications, especially pain relievers. These drugs are intended for use only in extreme situations where other medications fail to work, and they require a prescription. Patients using these medications often need careful supervision to prevent misuse.

Opium and its derivatives, as well as methadone, are used in medical applications. Opium has strong properties as a painkiller, while methadone reduces unpleasant symptoms of opiate withdrawal.

Schedule III


Schedule III drugs are used in medications and medical treatments without side effects from normal use; however, misuse can quickly lead to adverse side effects. Schedule III drugs contain most of the substances that directly affect the central nervous system, either as a stimulant or a depressant.

Those prescribed these medications should be supervised carefully by physicians to monitor for misuse or potentially adverse side effects. Some of the more recognizable drugs classified as Schedule III include codeine and reduced amounts of morphine and opium when they are mixed with other drugs to provide modified potency and effects.

Schedule IV

Schedule IV contains substances that are used more often in medications, as they have almost no side effects during normal use. Additionally, these drugs are not often misused in the same manner that other drugs are.

The substances are usually found as ingredients in medications to enhance the effectiveness of other ingredients. It is uncommon to interact with the substances on Schedule IV, unless as an ingredient in a medication.

Schedule V


Schedule V contains a wide range of substances, including drugs from other schedules in minimal amounts. These amounts are so minor that it is difficult to get the full effect of the drug unless it is taken in a significant amounts. Schedule V drugs include medications used as an ingredient in other pharmaceuticals.

These drugs include any substances that include less than 200 mg of codeine, or less than 100 mg of dihydrocodeine and ethylmorphine per 100 g of the substance. According to the Cochrane Database of Systematic Reviews, these medications are primarily used in postoperative settings.  This includes substances that include less than 2.5 mg of diphenoxylate with 25 mg of sulfate per dose. Opium is included when it is in a substance at a rate of less than 100 mg per gram of the overall substance.

Schedule V drugs present the lowest potential for abuse, and most are easily available, such as antidiarrheal medications or over-the-counter painkillers.

Reassessing Schedules

While the five-schedule system has seen widespread use and success in establishing a guideline for categorizing drugs, there are several provisions regarding the rescheduling and reassessment of drug schedules. The Attorney General of the United States has the ability to make temporary changes to the schedules in response to emerging situations, including the development of a new drug.

According to the Federal Register, the DEA can change the classification of a drug based on more current information. For instance, hydrocodone combination products were changed to Schedule II status from Schedule III status in 2014, based on the increased rates of hydrocodone abuse, addiction, and overdose.