BACKGROUND: In view of the theoretical rationale for beneficial effects of DHEA and DHEAS on cognitive function in ageing and dementia, we have undertaken a thorough investigation of well-conducted studies in this area. This will provide a basis for confirmation of any effect of DHEA/S administration in humans in properly controlled trials. The review will also provide a scientific basis for effective dosage, acceptable route and duration of administration, and side effect profiles. This review is especially pertinent at this time as DHEA is currently being sold in large quantities in health food stores, particularly in the USA. In some cases the recommended dose is different for men and women (50mg/day for men and 25mg/day for women) and the basis for this recommendation needs to be explored. OBJECTIVES: To establish whether administration of DHEA, or its sulphate, DHEAS, improves cognitive function or reduces the rate of decline of cognitive function in normal older adults or in individuals with dementia. SEARCH STRATEGY: Relevant electronic databases, journals, personal communications and conference abstracts were searched for randomised controlled trials investigating the effects of DHEA/S on cognition in older adults. SELECTION CRITERIA: All relevant randomised controlled trials of DHEA/S were considered for inclusion in the review. DATA COLLECTION AND ANALYSIS: Data for the specified outcomes were independently extracted by two reviewers (FAH & JvN) and cross-checked. Any discrepancies were discussed and resolved. No data pooling was undertaken owing to the lack of availability of the relevant statistics. MAIN RESULTS: There are four included studies, three cognition in normal older people, and Barnhart 1999 in perimenopausal women with decreased well-being. There were no studies in dementia. There were a few significant findings. Wolf 1997 found significant improvement following DHEA compared with placebo in both immediate recall (MD 0.8, 95% CI 0.16, 1.44) and delayed recall (MD 0.9, 95% CI 0.09, 1.71) of a visual memory test in women, estimated in a crossover trial after 2 weeks of treatment with each of DHEA and placebo. However there was no significant improvement in men, nor a significant effect on a verbal memory test. There was also no significant effect on four other cognitive tests. Wolf 1998 (2) found that placebo group performance deteriorated significantly on a test of selective attention following a psychosocial stressor (p<0.05), while deterioration was not evident in the DHEA group (p=0.85) after two weeks of treatment. However, when compared to placebo, DHEA produced a significant impairment on a visual memory test (p<0.01) following the stressor. No significant effect was found on a third cognitive task. Effects were not found on tasks when administered in the absence of a stressor. Barnhart 1999 employed three cognitive measures and found no significant effect of DHEA compared with placebo at 3 months. Findings to date suggest that DHEA replacement seems to be well tolerated with an absence of significant side-effects. REVIEWER'S CONCLUSIONS: The data offer no support at present for an improvement in memory or other aspects of cognitive function following DHEA treatment in normal older people. In view of the growing public enthusiasm for DHEA supplementation, particularly in the USA, and the possibility that any neuroprotective effect of DHEA/S may only be evident in the long term, there is a need to undertake high quality trials in which the duration of DHEA treatment is longer than one year, and the number of participants is large enough to detect effects if they exist. Recently, trials of DHEA supplementation in Alzheimer's Disease (USA), post-menopausal women (USA), normal older men (UK), and a one-year trial in normal older men and women (France) have been completed. As soon as the results are available these studies will be included in the review.