Is it really crystal clear that using methamphetamine (or other recreational drugs) causes people to engage in unsafe sex?

Many studies have found associations between unsafe sexual behaviour and use of crystal methamphetamine (and many other recreational drugs). Researchers and authors of relevant articles in popular media have often interpreted these associations as meaning that using 'crystal' directly causes people to engage in unsafe sex, and that interventions should aim to reduce crystal use in order to reduce the prevalence of sexually transmissible infections such as HIV. There is consistent evidence that crystal users are a high-risk group in terms of sexual behaviour. However, most relevant studies have provided only circumstantial evidence regarding a causal relationship. Promoting the idea that a particular recreational drug is a major direct cause of unsafe sex may have the unintended adverse effect of creating an excuse for engaging in unsafe sex, thereby increasing its use, and may incur opportunity costs by preventing limited available health promotion resources from being directed more usefully. This paper examines the limitations, in terms of demonstrating causality, of various types of study that have been published on this topic in relation to crystal use in particular. Researchers who investigate relationships between recreational drug use and behaviour, including sexual behaviour, should be careful about the wording of their conclusions and recommendations, and should consider the possibly counterproductive ways in which their findings might be represented in the media.