Scottish Government

4 Size and Value of Illicit Drug Market

4.1 Introduction

In this section we consider information on the amounts of drugs that drug users in Scotland would typically be using and combine this information with the prevalence estimates described in the previous section to provide estimates of the total amount of drugs used in Scotland in 2006. This amount will be considered as the street amount recognising the fact that for some drugs, the actual substance purchased by the end users would not be 100% pure. As we also have pricing data (of street drugs) we can estimate a monetary value for the total amount of drugs used, thus estimating the financial size of the market along with the physical size of it. All details of this analysis along with information on the data sources used can be found in the excel file accompanying this report.

4.2 Method for estimating the size of the illicit drugs market

The method for estimating the size of the illicit drugs market is based on quite a simple premise: combine information on the number of people using drugs with the amount they typically use to estimate the total amount of drugs used in the country. Combining this with information on the average price of drugs then allows a monetary value for the size of the market to be derived. Indeed, the approach is so straightforward you can skip a stage by directly combining information on the amount spent on drugs with the number of drug users to get the monetary value, and then use price estimates to calculate backwards to get the total amount used.

The actual analyses are, however, not so simple. They need to take into account difficulties in obtaining reliable estimates of the numbers of drug users; not just an overall total but numbers split by different types of drug (including those who use more than one type of drug). They also need to recognise that different types of drug user typically use differing amounts of drug and thus spend different amounts on drugs. This is obvious when comparing a 13 year old who has, on a few occasions, smoked a cannabis joint with a heavily addicted heroin user who injects their drugs several times a day. This issue becomes a bit more difficult when we begin to consider the point at which regular use of a substance could be considered problem use.

We therefore combine information on the number of drug users, split into the two groups of recreational users and problem drug users, with estimates of the amount of the drug used within a given year. We obtain the estimated amount of drugs used from a range of different sources, including the DORIS survey. Some sources provide information on the amount of a drug used within an individual drug use episode and this needs to be scaled up to provide information on the amount used per year by combining with information on the frequency of use.

4.3 Problem Drug Users

Heroin

From DORIS, problem drug users who use heroin use on average 64 days out of 90, which would equate to 261 days per year. On the basis of their responses within the DORIS survey, on average they use 0.89 grams per day, giving a total yearly use estimate (per heroin user) of 232 grams. Thus, the estimated 50,077 heroin users would use 11,635,465 grams of heroin (11,635 kg, or 11.46 tonnes). Data from the Scottish Crime and Drug Enforcement Agency ( SCDEA) suggest that heroin costs, on average, £47.35 per gram. Thus, the total cost of Scotland's heroin market is estimated to be £550,939,291 or £11,002 per heroin user.

There were a small number of respondents within DORIS whose average daily drug use amount appeared unfeasible. Those who were reporting unfeasibly large amounts of heroin per day (anything over an eighth of an ounce was assumed to be unfeasible) were removed from the analyses. Those who appeared to report very small amounts of heroin use (low outliers) were retained within the analyses as there was no strong justification for assuming that the responses were wrong.

The reported amounts used within the Scottish Drug Misuse Database were also examined. Again there were responses that were unfeasibly large. Perhaps it is the larger sample in the Scottish Drug Misuse Database or the possibility that those entering the DORIS data could more easily check back with the interviewer if there was any confusion about the amount, but there were proportionately more responses in the Scottish Drug Misuse Database that did not appear to be feasible. That was one reason why we did not use the Scottish Drug Misuse Database to estimate the amount of heroin (or indeed other drugs) used in a typical drug using day by problem drug users. The other reason is that there is a suspicion that problem drug users presenting at services may exaggerate their levels of heroin use in order to obtain a larger methadone prescription.

Other Drugs

The approach taken to estimate the number of days a problem drug user typically uses heroin was also taken for other drugs. Table 4.3.1 presents information from DORIS on the mean number of days per year a problem drug user uses specific drugs. The median and semi-interquartile range is also presented.

Table 4.3.1 Average number of days used in last 90 days by drug type

The amount used on a typical drug using day (episode) for drugs other than heroin was also derived from the DORIS sample, as shown in Table 4.3.2, again with the median and semi-interquartile ranges.

Table 4.3.2 Average amount used per drug using day (episode) by drug type

There are assumptions relating to the average amounts used for a typical day that they use those drugs ( i.e. drug using episode). One main issue (which is expanded upon below) is that many DORIS respondents reported their levels of drug use, particularly heroin use, in monetary terms rather than by weight. We therefore had to convert the monetary amount into a weight using a fixed price per gram as suggested by the SCDEA price estimates. Appendix 1 presents a summary of the issues when converting monetary expressions of the quantities used into weights.

This fixed amount per gram, which was calculated by taking the average of all reported prices from all Police Force areas, is likely to be an overestimate in some parts of the country and an underestimate in others. Moreover, the fixed amount relates to 2006 prices and not 2002/03 prices, the prices that drug users would be paying for their drugs when the first round of DORIS interviews were carried out. These issues were more pertinent for heroin use, but there are similar issues for the other drugs. For powder cocaine we would sometimes need to estimate how much cocaine would be in a typical 'line'. We took this value from an internet site ⁴ where it was suggested that the average 'line' contained between 35 and 100 milligrams of cocaine. We therefore assumed that there was 70 milligrams in a typical 'line'. Similarly we had to estimate how much crack cocaine would be in a typical 'rock'. This was derived directly from the DORIS data which suggested that there was, on average, 0.1 grams per £10 in rocks costing less that £100, 0.2 grams per £10 in rocks costing between £100 and £500 and 0.35 grams per £10 in rocks costing more than £500. Information on the average amount of amphetamines in a 'wrap' was also found on the internet, this time from the Independent Drug Monitoring Unit ⁵. It was assumed that there was 1 gram of amphetamine in the average wrap. As ecstasy is reported in this study as per tablet and not per gram, this issue does not arise for that drug. For cannabis it was assumed that there was 0.35 grams of cannabis in a joint. Sufficient data to split the reported amounts of cannabis use into herbal cannabis use (including skunk) or cannabis resin were not available from DORIS, or indeed any other readily available data source. Separate pricing data (and amounts in weight in a joint) were available from the Independent Drug Monitoring Unit website, however, this could not be used without separate information on amounts used. We therefore assume that the 0.35 grams per joint is a suitable estimate for the average amount used, whether it be herbal cannabis, skunk or cannabis resin.

There is, however, a greater issue with estimating the amount of benzodiazepines that a problem drug user uses in a typical day, as we are combining information about diazepam and temazepam use. We have examined the responses for diazepam use and temazepam use and used the higher amount for both the number of days (in the last 90 days) used and also the amount used per episode. Thus, in effect, we are ignoring any poly drug use (particularly within a specific day) where an individual uses both diazepam and temazepam.

4.4 Recreational Drug Users

In terms of the non-problem use we have had to resort to what Pudney has done and trawl the published and grey literature for average amounts used by non-problem users. One particularly useful source was the Independent Drug Monitoring Unit, a private company that, amongst other things, provides expert witness statements for courts, particularly on what typical amounts of personal daily use would be.

There were difficulties in estimating the number of days per year that an individual, who is not a problem drug user, uses particular drugs. The Scottish Crime and Victimisation Survey does not have enough respondents to examine this issue (apart from for cannabis use as we consider below). We use data from surveys carried out by the Independent Drug Monitoring Unit ( https://www.idmu.co.uk). They group their respondents into the following frequency of use in the last year categories:

• Ten times or less
• More than ten times but not monthly
• Monthly but not daily
• Daily

It is difficult to accurately convert the responses from these broad categories into actual quantities used per year, but we have made the following assumptions. If someone responded that they used ten times or less per year, we assumed that they, on average, used 5 times in a year. For those in the second group, we assumed that they used 11 times in a year. The monthly but not daily category is quite wide and we have assumed that this could cover anyone who uses from 12 days per year (i.e.once a month) up to 364 days a year. The average would therefore be 188 days per year. Combining the proportions from IDMU with these assumed averages we get the following:

Table 4.4.1 Estimated average number of days used per year for specific drugs

We also carried out an analysis from the Scottish Crime and Victimisation Survey (for those that suggested that cannabis was the drug they used most). The frequency groupings for that survey appear more useful. However the results from the Scottish Crime and Victimisation Survey suggest that the average cannabis user uses the drug 144 times per year. It may be that the sample in the Scottish Crime and Victimisation Survey under-represents those who use cannabis more frequently (or those that admit using cannabis under-report the amount they use).

In terms of amounts used per typical day by non-problem drug users, there is very little information available. For cannabis use, we used data from the Independent Drug Monitoring Unit which suggested that the average user uses 1 gram of cannabis per day. Again this has to be taken as an average over the different types of cannabis (herbal, skunk and resin). For amphetamines, it was taken to be 1.3 grams per day (Boys et al, 2002). For ecstasy, it was taken from the Independent Drug Monitoring Unit at an average of 2.92 tablets per day. Finally for benzodiazepines, it was taken as 0.07 grams per day, also from the Independent Drug Monitoring Unit website.

Price data

The price data comes primarily from the SCDEA, apart from the price estimates for Benzodiazepines. The SCDEA data contained price information from each Police Force area in Scotland for a range of quantities and types of drug. Even though there are significant geographical variations in price it was not possible to allow for this in the model. It was also not possible to determine the average quantity bought by users of the varying drugs from the available sources that could determine what price supplied by the SCDEA to use. Therefore the price used for each type of drug was calculated by taking the average price of all quantities given by the SCDEA that could be considered for personal use. These thresholds were taken from a consultation paper produced by the Home Office (2006). Although not used in regulation, these threshold levels are the only suggested levels available. In the absence of other information, this was used. As previously mentioned this average price will likely be an underestimate in some Police Force areas and an overestimate in others. A discussion on all of these issues raised above can be found in the discussion section at the end of this chapter.

The price per pill for benzodiazepines was taken to be 50 pence, with 10 milligrams taken to be the amount in the typical pill. This was primarily derived from information on diazepam. Other pricing and amounts used data that could be derived specifically for temazepam but as it is not possible to differentiate between diazepam and temazepam use in other aspects of the study, the 50 pence per 10 milligrams price was used for both drugs. This price does not however appear to contradict the available pricing data for temazepam. There were, however, some fairly major differences between the benzodiazepine pricing data on the Independent Drug Monitoring Unit website and the range of other websites with benzodiazepine pricing information. Where most websites suggest that 50 pence per pill seems appropriate, the Independent Drug Monitoring Unit website seems to suggest that the price would be about 50 pence for 20 pills. This was not seen as credible. Therefore we assumed a price of 50 pence per 10 milligrams, or £50 per gram.

The price data used in this study is presented in Table 4.4.2

Table 4.4.2 Price estimates for specific drugs

We are assuming that price data for problem drug users is the same as for non-problem drug users. However, as discussed later, this assumption may not be valid if problem drug users are able to source their drugs at a lower price than those who use drugs on a less regular basis.

4.5 Results

The total amount of illicit drugs consumed and the total amount spent on illicit drugs by all recreational and problem drug users in Scotland was estimated for each type of drug using the methods described in previous sections. The results are first summarised for problem drug users in table 4.5.1 below.

Table 4.5.1 Summary of the analyses to estimate the size of the problem drug use drugs market in 2006

Given that different units of measurement are applied to different types of illicit drugs, it does not make sense to estimate the total quantity of illicit drugs consumed by PDUs. However it does makes sense to do so when examining the total amount spent and it was in fact estimated that problem drug users in Scotland spent a total of around £900m in 2006. Since we have estimated that there are 55,328 problem drug users in Scotland, this equates to around £16,000 per PDU.

Comparisons between the amounts spent on different types of illicit drugs show that heroin has by far the biggest share of the market with around £550m being spent on it in 2006. This equates to 61% of the problem drug use market as shown in figure 4.5.1 below. Second to that is crack cocaine with PDUs spending around £180m and equating to 20% of the market. The remaining six types of illicit drug together make up the residual 19% of the market.

Figure 4.5.1 Percentage value of the problem drug use market attributed to specific drugs

Table 4.5.2 below shows the recreational drug market to be just over half the size of the problem drug market in terms of value where it was estimated that recreational drug users spent around £500m in 2006. Powder cocaine and cannabis have the largest shares in the recreational market in almost equal measure with recreational drug users spending around £210m each in 2006. This equates to around 40% of the recreational drug market as shown in figure 4.5.2.

Table 4.5.2 Summary of the analyses to estimate the size of the recreational drug use drugs market

Figure 4.5.2 Percentage value of the recreational drug use market attributed to specific drugs

In combining both the problem and recreational estimates above, it is possible to estimate the total size of the illicit drugs market in Scotland in 2006. Table 4.5.3 below shows that drug users in Scotland spent around £1.4bn on illicit drugs in 2006. Once again heroin holds the largest share of the total drugs market where the estimate of around £550m equates to 39% of the total illicit drugs market (see figure 4.5.3). Cannabis holds a 19% share, the second largest, of the total illicit drugs market with a total of nearly £270m being spent on the drug in 2006. This is followed closely by powder cocaine, which holds a 17% share of the market with an estimate of just under £250m spent on powder cocaine in 2006.

Of the total £1.4bn spent on illicit drugs in Scotland, 63% was by problem drug users and the remaining 37% by recreational drug users. This is shown graphically in figure 4.5.4.

Table 4.5.3 Summary of the analyses to estimate the size of the total drug use drugs market

These figures represent our best estimate of the size of different drugs markets based on the available data and given a range of plausible assumptions. However, as we emphasise in Appendix 2, the results are highly sensitive to the assumptions adopted and the "true" market size could be much higher or lower than suggested here.

Figure 4.5.3 Percentage value of the total drugs market attributed to specific drugs

Figure 4.5.4 Percentage value of the total drugs market attributed to problem drug users and recreational drug users

4.6 Data recommendations

The data used to estimate the size of the illicit drug market in Scotland comes from a range of sources, none of which were specifically established in order to size the drugs market. The first step in the process was to divide the drug using population of Scotland into two groups which we have labelled problem drug users and recreational drug users. As previously discussed, labelling the groups as such is not without problems; however it was a necessary step in creating a model with which to estimate the size of the drugs market. This is primarily because the available data used to inform the model often comes from a range of studies. Some studies focus on problem drug users (such as the national prevalence study or the DORIS study) while other studies do not specifically target heroin or crack cocaine users in their sampling (such as the SCVS) and thus may be more suitable to quantifying recreational drug use.

In terms of problem drug use, the prevalence information was derived by combining the national prevalence study (which estimated the number of opiate and / or benzodiazepine users in Scotland in 2006) and the DORIS study which asked a specific sample of drug users who were entering treatment (possibly for the first time) about the drugs they had been using in the previous 90 days. It is possible that the DORIS survey did not accurately reflect the true levels of drug use by Scotland's problem drug users, either because the sample was not representative of all problem drug users or, since the survey was carried out in 2002, is outdated. There may be bias in the results of DORIS as respondents may have not recalled their drug use accurately, either on purpose or simply because they had forgotten. Without carrying out individual prevalence studies for each of the drugs considered within the problem drug use definition it seems likely that deriving the number of problem drug users who use, for example, illicit methadone will need to be done by combining national prevalence estimates with either a representative survey of problem drug users or information from the Scottish Drug Misuse Database. It is clearly a recommendation of this study that any future estimates of the size of the drugs market in Scotland need to be informed by the results of future national prevalence studies. Studies have, so far, been carried out on a three-yearly basis (2000, 2003 and 2006) and if there is to a 2009 study then planning for it should be carried out as soon as possible. Clearly if a future prevalence estimation study takes a different approach to estimating prevalence then there will be issues about the comparability of the prevalence estimates and therefore the comparability of any resultant estimates of the size of the drugs market. Given the disparity in the responses (between the DORIS survey and the Scottish Drug Misuse Database) of problem drug users about their use of drugs other than heroin, there should be further studies done to look into this issue.

Both of the sources of information about the prevalence of recreational drug use (the SCVS and SALSUS) are part of ongoing series of studies that should continue to examine levels of drug use in the general population. All general population surveys are open to criticism about their ability to quantify a covert and illegal activity such as drug use; however we feel it is beyond the scope of this project to make recommendations about these series of studies, other than that they should continue to provide high quality information on the levels of use of drugs in the general population.

One issue that did arise (and which is discussed in Appendix 1) is how to accurately gauge the amounts of drug used from surveys such as DORIS. This was particularly pertinent in the case of heroin use, where many respondents quantified the amount they use in 'tenner bags'. Certain assumptions were needed in converting these responses into weights and the validity of the assumptions could be questionable and subject to variation over time and area of the country. For example a tenner bag in Glasgow could weigh more, or less, than a tenner bag in Aberdeen and it could perhaps be assumed that if the street price of heroin increased over time, then the amount in a tenner bag would decrease. A second issue that arose when examining the amounts of drugs the respondents in DORIS used was what to do with reported levels of daily drug use that appeared unfeasibly large. We have simply removed such unfeasibly large amounts from our analyses, something that may have skewed the results. A similar issue occurred within the Scottish Drug Misuse Database data; a data source we did not use to provide information on an average amount of drugs a problem drug user uses per day but does collate such information. Further work may be worthwhile in comparing the information from the Scottish Drug Misuse Database with other sources of information on the average daily amounts of drug use by problem drug users to see if this database can inform future studies.

The biggest issue with the data used to inform the models used to size the drugs market was about the amounts of drugs used by recreational drug users. The source of much of this information was from the Independent Drug Monitoring Unit which describes itself as a drug prices research company that conducts large scale drug user surveys throughout the UK and on the internet. We based the average amount of cannabis a user uses per day on information from that source. It is stated that the mean amount of cannabis used per day is 1 gram, however it is difficult to judge how appropriate it is to use that figure, given that a paper by Boys et al (2002) suggests the mean amount used per day is 1.58 grams. Further work is needed to refine the estimated amounts used per day, particularly by recreational drug users.

Finally we have needed to use the same prices of drugs, regardless of whether the person purchasing and consuming the drug is a problem drug user or a recreational drug user. It could perhaps be argued that different types of drug users are able to buy drugs at different prices. The price data we have used has come from the SCDEA and did not differentiate between the prices paid by problem drug users and those paid by recreational users. There may be merit in examining the price data from other sources, and the surveys carried out by the Independent Drug Monitoring Unit may be useful, particularly if they can be used to examine prices in Scotland.