Opiates include morphine, pethedine, heroin and derivatives of the opium poppy, as well as synthetic opiates such as methadone. The research on long term effects of opiates is limited. Some researchers have found long term opiate users to have impaired visuospatial and visuomotor functions. Other research has related long term use of opiates to high level cognitive impairment affecting the brain's ability to integrate and coordinate a range of cognitive skills.