The paradoxical psychological effects of LSD

This study examined the psychological effects of LSD during the acute drug state as well as any residual effects experienced two weeks later.

Using experimentally-validated questionnaires, the researchers found that the acute effects of LSD resembled certain aspects of psychosis, such as delusional thinking, yet these did not persist once the effects of the drug wore off. However, other elements of the LSD experience, such as heightened mood, appeared to be much longer-lasting, as participants continued to show increased optimism and openness two weeks after taking the drug. 

These findings indicate that the immediate effects of LSD may provide a useful tool for studying psychosis, and that the longer-term effects of the drug tend to generate improved psychological wellbeing.