The purpose of this study is to learn more about the changes in the activity of genes in cells sampled from healthy individuals treated with lithium. By studying these cellular changes, the investigators hope to understand if lymphoblastoid cell lines are valid tools in psychiatric genetics research. Specifically, the investigators want to see how specially treated lymphoblastoid cell lines are influenced by external conditions and specifically lithium treatment at the moment of sampling. To do so, the investigators will measure the gene expression (i.e. how much gene is in the cell) of lymphoblastoid cell lines and compare the levels between those sampled before and after one month of lithium treatment.