The addition of acidic substances to brown street heroin to facilitate the solubility of diamorphine in the injection preparation process is commonplace amongst UK injectors. Knowledge of the chemistry behind this process supports the need for this stage in the injection preparation process. It is currently illegal, under the Misuse of Drugs Act 1971, section 9A, to supply acidifiers and other paraphernalia to injectors in the UK. In the current climate of evidence-based practice, any consideration given to changing the law would look for evidence to illustrate that the paraphernalia was necessary. Although the theory behind the use of acidifiers suggests they are essential, no previous work using street heroin has actually been reported to illustrate this fact. Anecdotal information has found that drug users are being told by some service providers that the addition of acids is unnecessary. It is important that drugs services give credible information to their clients. The provision of inaccurate information in one area may lead to a lack of trust of all information provided. The small study reported here investigated, under controlled laboratory conditions, the effects of citric and ascorbic acids (vitamin C) on injections prepared with brown heroin, in order to demonstrate the need for acidifiers in the injection preparation process.