This report describes two patients who presented with severe type B lactic acidosis and shock, initially thought to be due to bowel ischaemia/myocardial infarction and pulmonary sepsis, respectively. This led to a delay in the diagnosis of thiamine deficiency. In both cases there was a dramatic response to intravenous thiamine, confirming the diagnosis of Shoshin beriberi. Both patients admitted to drinking home-brewed alcohol during the time of COVID-19 restrictions on alcohol consumption. These cases highlight the need for early diagnosis and immediate empirical treatment with intravenous thiamine in patients presenting with unexplained severe metabolic acidosis and circulatory shock.