Background: Given the bioactive properties and limited work to date, Hericium erinaceus (Lion’s mane) shows promise in improving cognitive function and mood. However, much of the human research has concentrated on chronic supplementation in cognitively compromised cohorts. Objective: The current pilot study investigated the acute and chronic (28-day) cognitive and mood-enhancing effects of Hericium erinaceus in a healthy, young adult cohort. Design: This randomized, double-blind, placebo-controlled, parallel-groups design investigated the acute (60 min post dose) and chronic (28-day intervention) effects of 1.8 g Hericium erinaceus in 41 healthy adults aged 18–45 years. Results: Analysis revealed that following a single dose of Hericium erinaceus, participants performed quicker on the Stroop task (p = 0.005) at 60 min post dose. A trend towards reduced subjective stress was observed following 28-day supplementation (p = 0.051). Conclusions: The findings tentatively suggest that Hericium erinaceus may improve speed of performance and reduce subjective stress in healthy, young adults. However, null and limited negative findings were also observed. Given the small sample size, these findings should be interpreted with caution. Further investigation in larger sample sizes is crucial, however the findings of this trial offer a promising avenue of interest.