Objective: To present an economic evaluation of a hypothetical national school-based drug prevention program based on the Gatehouse intervention.

Methods: Gatehouse intervention was compared to ‘current practice’. A 17-state Markov model that simulates the experience of 10-year-old Australian children in 2003 for 90 years was constructed to estimate the annual cannabis use prevalence at four levels: non-use, light use, weekly use and daily use. By applying the relative risks according to the different levels of use, three probable consequences were modelled: schizophrenia, heroin and poly-drug use and road traffic accidents. The potential health benefit was calculated using Disability Adjusted Life-Years (DALYs). The intervention effects were modelled by applying the same efficacy as found in the original trial (OR=0.71; 95%CI:0.52,0.97) to the initiation of cannabis use for individuals aged between 14 to 18 years in the participating schools. Costs associated with the implementation were calculated by scaling-up resource use as specified in the trial and adding additional costs required for a national program (eg.co-ordination activities). The anticipated cost-offsets attributable to health consequences that would have incurred in the absence of intervention were incorporated, with or without the inclusion of drug consumption cost estimates. An annual discount rate of 3% was incorporated for future benefits and costs. Both probabilistic uncertainty and sensitivity analyses were performed.

Results: Preliminary findings suggest that a national Gatehouse intervention could avert an estimated 1,194 DALYs at a cost of approximately $41.2 million over the 2-year intervention period. This corresponds to a median incremental cost-effectiveness ratio (ICER) of $34,800 per DALY averted. The intervention was considered a ‘dominant’ intervention (more health gains plus overall cost-savings) compared to current practice when the cost-offsets included drug consumption costs.

Conclusion: Using the efficacy observed in the trial, the Gatehouse intervention is likely to be cost-effective if implemented nationally in Australia.