From the actual NTSB report:

Potentially Impairing Drugs: This drug type included prescription and over-the-counter (OTC) drugs that, with typical therapeutic use, produce typical effects that could diminish a pilot’s cognitive or psychomotor performance. Illicit drugs and controlled substances were also included. Additionally, certain drugs not currently approved by the US Food and Drug Administration (FDA) have typical psychoactive effects known to adversely affect cognitive and psychomotor performance. These drugs were also classified as potentially impairing.

Drugs Used to Treat Potentially Impairing Conditions: This drug type refers to drugs used to treat medical conditions that may affect a person’s performance. A conservative approach was taken to identify the drugs in this category, with attention to maintaining consistent classification with previous NTSB reports for ease of longitudinal comparison (NTSB 2020a, 2014). For example, although cold or allergy symptoms may impair performance, antihistamines and decongestants were not classified as indicating a potentially impairing condition. Drugs classified as indicating a potentially impairing condition included drugs used to treat depression, anxiety, seizures, migraines, and other neuropsychiatric conditions, as well as drugs used to treat nausea and vertigo, and sedating pain drugs. Among the cardiovascular drugs, only those primarily used to treat arrhythmias were classified as indicating a potentially impairing condition. Blood thinners and diabetes medications were not automatically classified as indicating a potentially impairing condition under the conservative assumptions of previous NTSB reports, and this was not changed

Although addiction to or withdrawal from illicit drugs may be impairing, illicit drugs (not used therapeutically) were not classified as indicating a potentially impairing condition. Although individuals may sometimes use FDA unapproved drugs in an attempt to treat symptoms of a medical condition, these drugs also were not classified as indicating a potentially impairing condition. No attempt was made to ascertain anything about the presence, degree, or success of treating any condition, and no attempt was made to ascertain if there was impairment at the time of the accident. 15 Section 2.1.3.2 of this report describes the specific drugs within the FDA unapproved drug category and whether they were considered potentially impairing. 16 A few drug classification changes were made to resolve minor inconsistencies within categories or between previous report iterations; these changes are noted in appendix A.

Safety Research Report Controlled Substances: All drugs that are federally regulated are divided into five schedules under the Controlled Substances Act based on the drug’s accepted medical use and potential for abuse or dependence. Drugs in Schedules II through V are available for medical use and for this research update were categorized as controlled substances. Examples include opioids used for pain treatment and benzodiazepines used to treat anxiety. All of the identified controlled substances were also classified as potentially impairing drugs. Illicit drugs (not used therapeutically), although controlled substances, were excluded from such classification for purposes of this report to keep the report’s discussion of controlled substances separate from the discussion of illicit drugs.

Illicit Drugs: This drug type, which also was a drug category as discussed in section 2.1.3.2 of this report, included Schedule I drugs that, according to the DEA, have “no currently accepted medical use and a high potential for abuse.”18 Their use can lead to psychological or physical dependence. Examples include heroin and delta-9-tetrahydrocannabinol (delta-9-THC), the primary psychoactive chemical in marijuana. In this research update, three Schedule II drugs—amphetamine, cocaine, and methamphetamine—and one Schedule III drug ketamine—were also defined as illicit when evidence indicated likely nonmedicinal use.

This research update did not otherwise evaluate whether drugs had been used illicitly. Illicit drugs were also classified as potentially impairing drugs. Importantly, pilots should not infer that they may safely or legally use a drug based on its classification in this report. Even drugs not classified under any of the above types may have impairing effects, may be used to treat impairing conditions, or may carry restrictions on use by pilots under FAA policy.