Inclusion Criteria:  Male or female Age 21-65 years At-risk for depression as measured by a score >6 on the UCLA 3-item Loneliness Scale Body Mass Index in the range of 18-30 Willing and able to give informed consent for participation in the study Registered with a GP and consenting to GP being informed of participation in the study Currently living in the UK and sufficiently fluent English to understand and complete the tasks Able to access and use a computer with Internet Able to complete online questionnaires and tasks  Exclusion Criteria:  Currently on any regular prescribed medications (except the contraceptive pill), unless unlikely to compromise safety or affect data quality in the opinion of the Investigator; History or current significant psychiatric illness (other than past [>6 months] episodes of depression or anxiety) Current alcohol or substance misuse disorder (< 6 months) History of, or current significant hepatic disease History of, or current significant neurological condition (e.g. epilepsy) History of haemorrhagic stroke or deep brain structures stroke Known hyperglycaemia/pre-diabetes Known hypersensitivity to the study drug (i.e. simvastatin) or sucrose Pregnant, breast feeding, women of child-bearing potential not using appropriate contraceptive measures Participation in a study that uses the same or similar computer tasks (apart from the N-back) as those used in the present study Participation in a study that involves the use of a medication within the last 3 months