Lithium (Li) is an alkali metal. First described as a mood stabilizer in 1949, it remains an efficacious treatment for bipolar disorders. Recent emerging evidence of its neuroprotective and neurogenic effects alludes to lithium's potential therapeutic use in stroke and neurodegenerative diseases. One intriguing clinical application is in the treatment of Alzheimer's disease. Ongoing clinical trials are evaluating lithium's abilities to lower tau and beta-amyloid levels in cerebrospinal fluid in Alzheimer's patients. Lithium reduces brain inositol levels by inhibiting the enzyme inositol monophosphatase. This suggests that inositol monophosphatase inhibition is a key mechanism of Li's therapeutic action and that design of new inositol monophosphatase inhibitors may be a practical strategy to create new compounds with Li-like therapeutic effects. Lithium reduces the severity of some behavioral complications of Alzheimer's disease (AD). And there are growing indications that Li may be of benefit to the underlying pathology of AD, as well as an array of other common CNS disorders, including stroke, Parkinson's disease, and Huntington's disease. Physiologically, it exists as an ion in the body. Despite these demonstrated and prospective therapeutic benefits, Li's mechanism of action remains elusive, and opinions differ regarding the most relevant molecular targets. Lithium inhibits several enzymes; significant among these are inositol monophosphatase (IMPase), glycogen synthase kinase-3 (GSK-3), and the proteasome. Lithium has a narrow therapeutic range, and several well characterised adverse effects limit the potential usefulness of higher doses. Acute ingestion in Li-naive patients is generally associated with only short-lived exposure to high concentrations, due to extensive distribution of Li throughout the total body water compartment. Conversely, chronic toxicity and acute-on-therapeutic ingestion are associated with prolonged exposure to higher tissue concentrations and, therefore, greater toxicity. Lithium toxicity may be life threatening, or result in persistent cognitive and neurological impairment. Therefore, enhanced Li clearance has been explored as a means of minimizing exposure to high tissue concentrations. Although haemodialysis is highly effective in removing circulating Li, serum concentrations often rebound so repeated or prolonged treatment may be required. Continuous arteriovenous haemodiafiltration and continuous venovenous haemodiafiltration increase Li clearance, albeit to a lesser extent than haemodialysis, and are more widely accessible. Lithium reduces brain inositol levels by inhibiting IMPase, suggesting that IMPase's inhibition is a key mechanism of Li's therapeutic action and that design of new IMPase inhibitors may be a practical strategy to create new compounds with Li-like therapeutic effects. (PMID: 17688381, 17316163, 8110911, 17288494).