How pure are street drugs?

There is no proper quality control over illegal drugs. It is often difficult to know whether a powder, pill, herb or liquid is a particular drug. Furthermore you may have no idea how strong the dose is or whether it contains other drugs or substances to bulk it out. Illegal drugs may contain:

  • Impurities – substances present in the drug as a natural result of how it was made rather than deliberately added. For example, opiate alkaloids may be present in heroin from refining opium into heroin.
  • Adulterants – these are drugs that deliberately mimic or enhance the effects of the drug being offered. Examples are the way caffeine and/ or ephedrine are often found in amphetamine or ecstasy.
  • Dilutents – these are mainly sugars such as glucose, lactose and mannitol. These are added to bulk out the deal and assist the process of dilution of the drug for injection.

While impurities and dilutents can, in themselves be dangerous, the likelihood of this happening has often been exaggerated. While rumours circulate about drugs cut with rat poison, strychnine and brick dust such contamination is rare. It is not in the dealer’s interest to have customers dropping dead from deliberately contaminated drugs. In contrast people will return to get drugs from dealers who offer good quality substances.

Purity levels

Back in 2014 the Druglink street drugs survey contacted police forces, drug workers, treatment services, drug expert witnesses and members of the Drug Expert Witness and Valuation Association from around the UK. The survey reported rising purity levels for heroin, cocaine and MDMA, and this trend was found to have continued in the 2016 DrugWise Street Drug Trends Survey. 

Bearing these purity levels in mind it is important to adhere to harm reduction advice when using these drugs and start with small amounts, such as a quarter of a pill, and wait for an hour or two before considering using more.

Please note that this is a guide to national patterns and should not be relied on to determine the content of substances circulating in your area. The purity of street drugs varies between different areas and can change within a matter of days.


As with previous years, the purity of amphetamine is low compared to drugs such as ecstasy. Even in the peak years, roughly 1997-2000, purity levels never rose above 15%; more usually they settle between 5%-10%.

An informant to our Street Drugs Trend Survey 2016 from Liverpool said:

“The purity level which drug powders level out to is the lowest which dealers can get away with, i.e. the level at which they can make most profit before users stop buying it because it has gotten too weak or too adulterated to inject and/or smoke and/or sniff. This varies with the drug (its chemistry and related effects). With heroin that seems to be around 20% to 30%, while for amphetamine it is more in the range 5% to 10%.”


Our survey found that purity levels for street cocaine (and therefore crack) are unprecedented with informants uniformly citing some purities regularly at anything between 70%-90%. Triangulating three laboratories testing UK-wide samples gives a UK average purity for cocaine at 64% and 74% for crack. Given that crack selling is an integral part of county line distribution, the reasoning behind the increased purity is probably similar as for heroin, despite the very different routes from producer country to street.

The two tier market in cocaine continues with prices at ‘student’, ‘pub dust’ or ‘monkey dust’ purity (the name depends on location) at around 40% and costing about £30-£40 a gram going up to around £80 a gram for purity in excess of 70%.


As with cocaine and heroin, purity levels for ecstasy have increased sharply over the past two years. Whereas in the early days of ‘rave culture’, the average dose was around 50-80 mg, now agencies such as the Welsh drug testing organisation WEDINOS and Police Scotland regularly report pill dosages in excess of 150mg and sometimes as high as 300mg


The heroin drought of 2010 resulted for a while in low grade heroin on the streets. Often cut with paracetamol and caffeine, purity levels averaged out in the mid-teens to low twenty per cent. By 2014, this had climbed in some areas to 40% while today, purity levels at 60% are being quoted. Triangulating data from three forensic laboratories reveals an average UK purity for heroin at 43%.

Further information on drug purity is provided in the United Kingdom drug situation: Focal Point annual report 2017 (PDF)

This report states:

“The average purity of powder cocaine at user-level in England and Wales has increased steadily over the last three years, from 36% in 2014 to a record high of 54% in 2016. Prior to this, purity had dropped steadily from 51% in 2003 to a low of 20% in 2009. Early indications suggest this trend will continue in 2017 (personal communication – NCA).

The conversion to crack cocaine occurs within the UK, therefore much of the supply-side factors affecting the purity of cocaine powder are the same for the base form. As such, the trend in purity of crack cocaine tracks that of powder (though crack purities are typically higher). Purity of user-level crack cocaine has risen from a record low of 26% in 2011 to 48% in 2015, and increased more sharply in 2016 to a record high of 71%. Early data from 2017 suggests that average purity remains exceptionally high.Heroin purity at user-level dropped from 35% in 2010 to a low of 18% in 2011 (the year in which supply was most affected by the heroin drought). Purity of heroin subsequently rose each year, more than doubling to an all-time high of 44% in 2015. The mean of 43% recorded in 2016 (as well as provisional data for early 2017) suggests that heroin purity has now stabilised, or perhaps even slightly decreased.”

A graph from the report illustrates changes in drug purity over time: