If you take one of the new "legal highs" in combination with another drug (an opiate such as heroin, say) it can be hard to predict the effects.
It is hard enough for those working with drug users to keep up with the effect of many of the novel psychoactive compounds appearing on the market, let alone the effects of so-called "poly drug use".
How does a drugs worker know about the effects of drugs as they interact with each other? The answer is perhaps surprising. "We talk to people who are using them," one told me yesterday. "That's how you find out, people saying 'this is what happened to me'."
It is hard to overstate the problems facing drug advice agencies in relation to so-called New Psychoactive Substances (NPSs). The term "legal highs" has become less appropriate with increasing Government efforts to control their sale and supply. However, the rapidity with which new substances are designed and marketed - often with very minor chemical changes, but with a change of name and potential changes to effects and side effects - makes it difficult for drug workers to respond.
Advice agencies which used to have to deal with a limited range of relatively traditional drugs now find that they are unsure about the names and effects of drugs clients are taking.
As a conference today on trends in drug use will hear, there is increasing concern about the rapid proliferation of NPSs. A leap in their use among existing problem drug users is one concern, with users of more established "downers" including heroin and diazepam, now taking up the new drugs in tandem with their existing habit.
But a survey to be revealed at the Scottish Drugs Forum event in Glasgow will also point to the considerable impact they are having on vulnerable young people. By talking to people outside drug work, SDF researchers assessed the impact NPSs are having on under-16s in touch with homelessness services, council services for care leavers, and young people with social work involvement in their lives.
They found 82% of workers in these sectors said NPSs were having a significant impact on the daily lives of young people they worked with. In many cases the effects were so severe it was making it difficult to work with them at all.
The most recent drug death statistics for 2012 did not flag up the immediate danger of NPSs. Of 47 deaths last year involving such substances, 32 of those cases involved other drugs, and in 15 cases NPSs definitely played no part in the death. In only two cases was it the only substance present.
But many drug workers don't feel they know enough about the long-term effects of such drugs. Asked what NPSs they were concerned about, workers came up with a huge list of names.
These young people could be Scotland's future long-term drug users, SDF director David Liddell told me. Drug agencies want to intervene earlier to prevent that.
But there is a pressing need for investment in research and training to equip traditional drug work services for a very different challenge.
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