LIthium as Bridging thErapy Prior to Radioactiveiodine in hyperThYroidism

Inclusion Criteria: Adult patients aged 18 years old and above with thyrotoxicosis who have been planned for definitive radioactive iodine: * consented for radioactive iodine as a definitive treatment * able to comply with requirement of radioactive iodine treatment * FT4 level below 40pmol/L Exclusion Criteria: * pregnancy or lactating mother * moderate to severe and active thyroid eye disease based on EUGOGO criteria, requires steroid cover * renal impairment, egfr \<45mls/min (stage 3b) * underlying activity malignancy * underlying active schizophrenia or bipolar disorder * patients on medication that may interact with lithium (refer appendix) * patients on medications that may interfere with radioactive iodine effectiveness such as amiodarone and less than a month of intravenous contrast medium * previous radioactive iodine less than 6 months * previous history of adverse effect following exposure to lithium or carbimazole * thyroid carcinoma