Some meta-analysis on smoking and risk of stroke showed that current smoking raised risks of total stroke, subarachnoid hemorrhage, and ischemic stroke but did not raise risk of intraparenchymal hemorrhage. On the other hand, previous meta-analysis showed that smoking was inversely associated with risk of Parkinson's disease. Early research found that nicotine improved short-term cognitive function and inhibited amyloid formation. More recently, it has showed with meta-analysis that smoking raised risk of Alzheimer's disease. Cigarette smoking has a disadvantage for neurological disorders.