Overall, two long-term effects—persistent psychosis and HPPD—have been associated with use of classic hallucinogens (see text box below). Although occurrence of either is rare, it is also unpredictable and may happen more often than previously thought, and sometimes both conditions occur together. While the exact causes are not known, both conditions are more often seen in individuals with a history of psychological problems but can happen to anyone, even after a single exposure. There is no established treatment for HPPD, in which flashbacks may occur spontaneously and repeatedly although less intensely than their initial occurrence. Some antidepressant and antipsychotic drugs can be prescribed to help improve mood and treat psychoses, however. Psychotherapy may also help patients cope with fear or confusion associated with visual disturbances or other consequences of long-term LSD use. More research on the causes, incidence, and long-term effects of both disorders is being conducted.
This process can be analyzed at the state level (see Peri and Sparber 2009). The analysis begins with the well-documented phenomenon that .-born workers and immigrants tend to take different occupations. Among less-educated workers, those born in the United States tend to have jobs in manufacturing or mining, while immigrants tend to have jobs in personal services and agriculture. Among more-educated workers, those born in the United States tend to work as managers, teachers, and nurses, while immigrants tend to work as engineers, scientists, and doctors. Second, within industries and specific businesses, immigrants and .-born workers tend to specialize in different job tasks. Because those born in the United States have relatively better English language skills, they tend to specialize in communication tasks. Immigrants tend to specialize in other tasks, such as manual labor. Just as in the standard concept of comparative advantage, this results in specialization and improved production efficiency.