This study aimed to evaluate the efficacy and safety of Ganoderma lucidum for the treatment of hyperglycaemia and other cardiovascular risk components of metabolic syndrome using a prospective, double-blind, randomised, placebo-controlled trial. Eighty-four participants with type 2 diabetes mellitus and metabolic syndrome were randomised to one of three intervention groups: Ganoderma lucidum, Ganoderma lucidum with Cordyceps sinensis, or placebo. The dosage was 3 g/day of Ganoderma lucidum, with or without Cordyceps sinensis, for 16 weeks. The primary outcome measure was blood glucose (glycosylated haemoglobin [HbA1c] and fasting plasma glucose [FPG]); a number of secondary outcome measures were also tested. Data from the two intervention groups were combined. The combined intervention had no effect on any of the primary (baseline-adjusted difference in means: HbA1c = 0.13%, 95% CI [-0.35, 0.60], p = 0.60; FPG = 0.03 mmol/L, 95% CI [-0.90, 0.96], p = 0.95) or secondary outcome measures over the course of the 16-week trial, and no overall increased risk of adverse events with either active treatment. Evidence from this randomised clinical trial does not support the use of Ganoderma lucidum for treatment of cardiovascular risk factors in people with diabetes mellitus or metabolic syndrome. This Clinical Trial was registered with the Australian New Zealand Clinical Trials Registry on November 23, 2006. Trial ID: ACTRN12606000485538 and can be accessed here: https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=81705.