'Day after' effects of pot smoking.

Fasten your seat belt: Pilots who get "high" on marijuana the day before taking control of an aircraft may have difficulty landing the plane safely, even though they feel alert and normal.

Furthermore, there is "a need for concern about the performance of those entrusted with complex behavioral and cognitive tasks within 24 hours after smoking marijuana," says Jerome A. Yesavage of Stanford University and his colleagues in the November AMERICAN JOURNAL OF PSYCHIATRY.

The investigators recruited 10 experienced private pilots and trained them on a computerized flight-stimulator landing task. All subjects had smoked marijuana before, but none was a daily user. They abstained from drug use for the test period, which began with a morning "baseline" flight. Each then smoked a marijuana cigarette containing 19 milligrams of tetrahydrocannabinol (THC), the active agent in marijuana. This is comparable to "a strong social dose," say the researchers. The landing task was repeated one, four and 24 hours later.

The worst performances compared with baseline occurred one hour after THC ingestion. But 24 hours later, the pilots still experienced significant difficulty in aligning the computerized airplane and landing it at the center of the runway. There were marked deviations from the proper angle of descent in the last 6,000 feet of the approach to landing, report the scientists. "In actual flight," they explain, "where there is wind and turbulence, such errors can easily lead to crashes." The pilots, however, reported no awareness of any marijuana aftereffects on their performance, mood or alertness.

It is not known how long it takes before people can perform complex tasks at baseline levels after smoking marijuana, note Yesavage and his co-workers. THC metabolites remain in the urine for up to 72 hours; plasma concentrations rapidly drop several hours after marijuana is smoked.

The widespread use of the drug suggests that pilot performance should be more closely studied, they say. More down-to-earth tasks, such as operating complicated heavy equipment or railway trains, may also be susceptible to a "day after" marijuana effect.

THC-positive urine screens have been found among railroad crews responsible for recent train accidents, note the researchers, and the pilot in a 1983 commercial air crash at Newark (N.J.) Airport was found to have smoked marijuana 24 hours before the accident. But at this point, they caution, data on the behavioral aftereffects of marijuana are preliminary.