Statins are among the most prescribed medications worldwide. Both beneficial (e.g. antidepressant and pro-cognitive) and adverse (e.g. depressogenic and cognitive-impairing) mental health outcomes have been described in clinical studies. The underlying neuropsychological mechanisms, whether positive or negative, are, however, not established. Clarifying such activities has implications for the safe prescribing and repurposing potential of these drugs, especially in people with depression.

In this double-blind, randomized, placebo-controlled experimental medicine study, we investigated the effects of simvastatin on emotional processing, reward learning, working memory, and waking salivary cortisol (WSC) in 101 people at-risk for depression due to reported high loneliness scores (mean 7.3 ± 1.2 on the UCLA scale). This trial was largely conducted during periods of social distancing due to the COVID-19 pandemic (July 2021–February 2023), and we employed a fully remote design within a UK-wide sample.

High retention rates, minimal outlier data, and typical main effects of task condition (e.g. emotion) were seen in all cognitive tasks, indicating this approach was comparable to in-person testing. After 28 days, we found no statistically significant differences (F’s < 3.0, p’s > 0.20) for any of the measures of emotional processing, reward learning, working memory, and WSC.

Study results do not substantiate concerns regarding adverse neuropsychiatric events due to statins and support the safety of their prescribing in at-risk populations. Although other unmeasured cognitive processes may be involved, our null findings are also in line with more recent clinical evidence suggesting statins do not show antidepressant or pro-cognitive efficacy.

Evidence suggests inflammation may be a key mechanism by which psychosocial stress, including loneliness, predisposes to depression. Observational and clinical studies have suggested simvastatin, with its anti-inflammatory properties, may have a potential use in the treatment of depression. Previous experimental medicine trials investigating 7-day use of statins showed conflicting results, with simvastatin displaying a more positive effect on emotional processing compared with atorvastatin. It is possible that statins require longer administration in predisposed individuals before showing the expected positive effects on emotional processing.

Here, we aim to test the neuropsychological effects of 28-day simvastatin administration versus placebo, in healthy volunteers at risk for depression owing to loneliness.

This is a remote experimental medicine study. One hundred participants across the UK will be recruited and randomised to either 28-day 20 mg simvastatin or placebo in a double-blind fashion. Before and after administration, participants will complete an online testing session involving tasks of emotional processing and reward learning, processes related to vulnerability to depression. Working memory will also be assessed and waking salivary cortisol samples will be collected. The primary outcome will be accuracy in identifying emotions in a facial expression recognition task, comparing the two groups across time.