Cocaine supplies to and within Australia increased after 2006-07, and there is some evidence that cocaine demand may also have risen. However, the extent, nature and public health implications of any changes in cocaine demand remain unclear. Equally unclear, is whether such changes may have been fuelled by declines in two of Australia's other stimulant markets. We examined general population trends in cocaine use and harmful practices and use of related stimulants between 1998 and 2010, and conducted age-period-cohort analyses using five repeated cross-sections of Australia's National Drug Strategy Household Survey. The results indicate past year cocaine use prevalence has increased significantly since 2004, to its highest point in the past 12 years; 2.1% in 2010. But frequency of cocaine use has not increased. Moreover, most harmful practices (injecting, high-quantity use) have remained stable. Changes in the cocaine market appear related to changes in the Australian methamphetamine and ecstasy markets, including declining purity of ecstasy. For example, the cohorts of people most likely to exhibit recent cocaine use were also most likely to have used ecstasy and methamphetamine (those born from 1976 to 1984). The findings indicate that an increase in cocaine demand does not necessarily lead to substantial increases in public health harm: and indeed that the public health implications from the recent increase are likely to be negligible. Moreover, the findings suggest changes to either ecstasy or methamphetamine supply may lead to more shifts in demand for Australia's cocaine market.