Background: The last decade has seen the emergence of a new phenomenon in recreational substance use with the availability of herbal and synthetic, unregulated, psychoactive drugs in the market place; alongside this, international concern has developed in relation to their use and associated harms. New Zealand (NZ) was one of the first countries to experience this new phenomenon, with products containing chemicals of the piperazine group – mainly benzylpiperazine (BZP) and trifluoromethylphenylpiperazine (TFMPP). In 2008, the NZ Government prohibited these substances, but allowed a 6-month amnesty period for possession. Our study aimed to obtain a measure of change in BZP use over time.

Methods: This study used a longitudinal, web-based survey, with data collected at two time points from the same participants. The first survey was carried out 3 months after BZP prohibition, and included retrospective questions for the 6 months preceding the survey. The second survey was conducted 9 months after prohibition and also included retrospective questions for the 6 months preceding the survey.

Results: 273 sets of paired data were identified. The use of BZP party pills (p < 0.0001) and legally available smokeable products (p = 0.002) reduced over time. A majority of users of party pills obtained them from friends or from their own stockpiled supplies. The misuse of prescription drugs (p = 0.02) increased over time, whereas statistically significant increases in stimulant or alcohol use were not noted.

Conclusion: Following prohibition of piperazine-based party pills, we noted a significant reduction in the proportions of participants using them. The observed increase in the misuse of prescription medicines may relate to their perceived ‘quality’, or as being less ‘illegal’ than illicit drugs.