"Since the memorable occasion upon which young Eve palmed off the green apple on old man Adam, more or less fraud in food handling has occurred, as opportunity offered and occasion for profit suggested. In the adulteration of drugs even more elasticity of conscience has been necessary to permit the almost unlimited sophistication which has been practice from time immemorial."

Hanson, 1896

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People use drugs. This is an inescapable reality that has been tormenting policymakers and legislators around the world. From ancient times, human beings seek altered states of consciousness, frequently via the use of psychoactive substances (Escohotado, 1999). People eat, swallow, smoke, snort, and inject drugs to amplify, numb or distort the senses and change mood, even if this involves some degree of risk to their health. Different governments have tried different approaches, some more liberal and others more punitive, to restrict this type of behavior (OSF, 2011). However, there is a considerable fringe of society that consumes, and will continue to consume, drugs (UNODC, 2016).

Almost as old as drug use is the adulteration of drugs, the intentional and unintentional addition of components which are not usually part of a given substance. History is full of reports of adulteration, some more dangerous than others (Cole et al., 2011). Prohibition and the desire for profit seem to go hand in hand with adulteration. In the 1930s over 50,000 people in the United States of America (USA) suffered from partial paralysis due to a spinal cord cellular damage related with the consumption of Jamaica ginger extract. Jamaica ginger was a medicinal extract of ginger root that was used for respiratory infections and digestion problems, but contained more than 70% alcohol (Morgan, 1982). After the USA's National Prohibition Act, which prohibited the production, sale and transport of alcohol, was enacted in 1919, Jamaica ginger became a popular and cheap way of getting intoxicated and circumventing prohibition.

To enforce prohibition, authorities soon required a change in the content of the medicine to make it bitter and difficult to ingest in order to discourage people from drinking it. In an effort to bypass prohibition the bootleggers started replacing the ginger contents with other substances that could make the medicine more palatable, and at the same time pass the analytical control done by authorities. One of the adulterants that became commonly used in the Jamaican ginger extract was trorthocresyl phosphate (TOCP), later discovered to be toxic and damage nerve cells. When the cause of the epidemic paralysis was detected it was already too late for several thousand victims (Morgan, 1982).

Ultimately, it was acknowledged that alcohol prohibition was not working for a considerable number of people and ignoring the law gained social tolerance. The incidents resulting from adulteration and the violence related with organized crime that surrounded the sale of illegal alcohol, contributed to a strong popular opposition to Prohibition that eventually led the act to be repealed.

In the USA, alcohol was able to regain its legal status, however the situation with many of the psychoactive substances used by people is still an illegal one as in most countries around the world.

The production of illegal psychoactive substances and their chemical precursors, usually also controlled, can be achieved through different synthetic routes, depending on starting materials, with the quality of the final product being highly dependent on the know-how of operators, their skills and available resources. Frequently the purification procedure is inadequate or even nonexistent, which leads to the presence of impurities or other active substances produced by parallel reactions. These, along with chemical degradation and contamination during distribution processes, are the main causes of unintentional adulteration (Coomber, 1997). The intentional addition of other substances seeks to increase product volume, enhance or mimic the psychoactive effects or even to facilitate drug administration (Broséus, Gentile, & Esseiva, 2016; Cole et al., 2011). The lack of control of drugs composition poses several risks to people who use drugs, leaving the non-medical market in a state of chemical anarchy.

In 1974 Joan Marshman wrote "Although an illicit market system for drugs has long been part of our society, recent years have brought significant changes in the street drug scene. Together with the introduction of a wide variety of hallucinogens, an increase in the proportion of relatively inexperienced adolescent users, and an unprecedented interest on the part of the news media, has come a situation in which drugs purchased on the street frequently do not contain the pharmacologically active material(s) alleged to be present" (p.v.). More than forty years ago Marshman exposed the link between the repeated introduction of new substances into the market, mainly to circumvent drug laws, and the increase in drug misrepresentation and adulteration and the dangers this may pose, particularly to more vulnerable people.

Acknowledging that drug adulteration was becoming a relevant public health problem, universities, non-governmental organizations (NGOs) and private companies felt the need to establish systems able to detect and identify substances, monitor these illegal markets, and inform the community.

North America
The first services using Drug Checking with harm reduction purposes go back to the 60s in the United States, Canada and Germany (Brown & Malone, 1973; Falck, 1981; Kealy & Webber, 1975; Marshman, 1974). In the seventies, in North America, several different programs were offering anonymous analysis services. Some of the most relevant projects set in motion in this period were: "The Pacific Information Service on Street Drugs", a project of the University of the Pacific School of Pharmacy that collected most of its samples in drug counselling centers rather than from individuals, reinforcing the importance of providing drug checking integrated within a larger harm reduction or prevention service, which could guarantee the usefulness and pertinence of the information people received along with the analysis result; Do It Now Foundation's community-based "Street Drug Analysis & Dope Info", with a hotline available at any time to provide information for people who wished to test; "Analysis Anonymous", a low-cost testing service based on the belief that "the public should have unbiased information about illicit ('street') drugs" (Brown & Malone, 1973, p.671) offered by the privately operated PharmChem Laboratories; "Anonymous Drug Analysis and Poison Control Center", a project of the University of Maryland School of Pharmacy, which was state funded; a service run by Midwest Research Institute, and several others that were working in different regions with identical purposes (Brown & Malone, 1973; Falck, 1981; Kealy & Webber, 1975; Marshman, 1974).

Most of these early drug checking services worked under specific principles and methodologies that are common to the majority of services running today, such as: the voluntary submission of samples, ideally offering testing free of charge to guarantee access to all social groups, the service should not suffer day-to-day interference by public authorities or law enforcement agencies, submissions of samples should be anonymous to deflect the possibility of legal consequences to service users, and results of analysis should be made available to potential drug users, health workers and anyone interested in the "drug problem", preferably along with information about safer drug use and harm minimization (Brown & Malone, 1973; Falck, 1981; Kealy & Webber, 1975). Eventually, after a few years running, these projects were shut down due to many of the same constrains most community-based drug checking services deal with today: legal, economical, technical, and particularly ethical/moral, in that these services are frequently seen by some quadrants of society as quality control to users and dealers, and hence stand accused of promoting the use of illicit drugs (Marshman, 1974).

Despite this harsh legislative environment towards drug checking initiatives, since 1999, several organizations in the United States and Canada have tried once again to offer people who use drugs the possibility of having their substances analyzed. In 1999 the American community-based "Ecstasy Harm Reduction Project", later renamed Dancesafe, began selling testing kits and initiated a laboratory pill analysis program, allowing people who use drugs to anonymously send MDMA tablets to a laboratory for gas chromatography/mass spectrometry testing. In 2001, Erowid launched an anonymous drug analysis program and began publishing test results via EcstasyData.org, incorporating earlier data from Dancesafe and MAPS (E. Erowid, personal communication, Aug 20, 2019). Today, Dancesafe offers onsite drug checking in several different electronic music events (Saleemi, Pennybaker, Wooldridge & Johnson, 2017). Other community-based organizations like TRIP! Project, MindBodyLove, Island Kids, ANKORS, Calgary PartySafe, Bunk Police, GRIP are also offering drug checking integrated services to partygoers (Sage & Michelow, 2016).

Europe
In Europe, the first drug checking services appeared along the development of the electronic dance music scene. In the early 1990s the Dutch government promoted and funded the Drug Information and Monitoring Service (DIMS) with the aim of monitoring drug markets and implementing harm reduction strategies (Brunt & Niesink, 2011).

In the following years several harm reduction projects, mainly promoted by civil society, started offering similar services across Western Europe including ChEckiT in Austria (Benschop, Rabes, & Korf, 2002), Safer Nightlife in Switzerland (Hungerbuehler, Buecheli, & Schaub, 2011), Energy Control and AI laket in Spain (Rovira & Ibañez, 2002), TechnoPlus, Mission XBT and Keep Smiling in France, Modus Vivendi in Belgium (EMCDDA, 2001), and Ares do Pinhal and CHECK!N in Portugal (Martins, Valente, & Pires, 2015).

In 2010, in the framework of the European project "Nightlife, Empowerment and Well-Being Implementation Project" (NEWIP), the Trans-European Drug Information Network (TEDI) was created allowing a collaboration between several European Union community-based projects offering drug checking services, and facilitating the exchange of information and good practices. The TEDI database "collects, monitors and analyses the evolution of the various European drug scenes and reports on them on a regular basis". Drug Checking organizations share their data on the T.E.D.I. database, which was originally established in conjunction with projects that worked directly with drug users." (Ventura et al., 2012, p.10).

The TEDI network began with eight members and has almost doubled its numbers in less than five years, including new drug checking services in countries such as the UK (The Loop, Wedinos), Luxembourg (PIPAPO), Italy (Neurotravel Project), Slovenia (Drogart), Germany (Legal high inhalts stoffe) and Portugal (Kosmicare Association).

Rest of the world
Recently, the appearance in the market of a very large number of NPS (EMCDDA, 2015) and the opioid crisis that is particularly striking in North America (Barry, 2018), has leveraged the piloting of several drug checking initiatives in countries like Canada, Mexico, Brazil, Colombia and Australia, and brought the discussion around this issue to the spotlight.

Bearing in mind all of these different implementation experiences of drug checking as a harm reduction strategy, and the growing number of new substances appearing each year, one could imagine that drug checking would be widespread and its potential and efficacy would be by now hardly questionable. However, the criticism around these services has not subsided and there is still a very long way to go until they are available to the majority of those who wish to use them.

Some of the more relevant critiques faced by drug checking initiatives comes from the European Monitoring Center for Drugs and Drug Addiction (EMCDDA), which in 2001 stated that drug checking, despite "serving as a cornerstone for projects that have been trying to reduce risks in the party scene, most services suffered from a lack of impact evaluation" (EMCDDA, 2001). More recently, Pirona et al. (2017, p.89) observed that "challenges in wider adoption of onsite drug checking include legal obstacles (...) and the lack of evidence of these interventions in reducing harmful use or changing risk behaviours". The authors also state that "the quality and efficacy of the chemical tests and associated harm reduction messages depends greatly on the technology available on-site, and on the timeliness of the results delivered to users." (Pirona et al. 2017, pag.89). Again, in 2017 the EMCDDA stated in the European Guide to Health and Social Responses to Drug Problems that "any assessment of these arguments (about drug checking services) is hampered by the lack of robust studies and the difficulty in generalizing given the very different approaches and models used" (EMCDDA, 2017, p.140).

Around the world, drug checking is being performed using several different techniques and the advantages and shortcomings of most of them have been widely discussed in the literature (Brunt, 2017; Harper, Powell, & Pijl, 2017; Martins et al., 2017; Schneider, Galettis, Williams, Lucas, & Martin, 2016). Several new techniques are being explored and combined to enhance the detection capacity of the drug checking services (BAONPS, 2017a; Brunt et al., 2016). It is imperative to underline that whatever the technique used, the analysis of illicit drug formulations does not assure the safety of the product or guarantee protection of the person from harm (Schneider et al., 2016).These analytical limitations must be clearly explained to clients of any integrated drug checking service, and drug checking as a harm reduction strategy should never be offered separately from a brief consultation or counselling that should focus not only on the test result but further explore the client's needs and wishes when using the service (Martins, Valente & Pires, 2015). This privileged moment of contact with people that use drugs is fundamental to any integrated service and its what clearly establishes that drug checking services are not purity or quality control services, highly dependent of the analytical technique, but a important and strategic integrated health response (Martins, Valente & Pires, 2015).

Although an advanced quantitative analytical technique is an important part of drug checking, particularly when facing challenges like high dosage MDMA or the appearance of so many highly potent NPS (Schneider et al., 2016), even techniques with low reliability such as thin layer chromatography and colorimetric reagents, when combined, can work as an important harm reduction tool if used with caution and fully incorporated in a wider harm reduction strategy that should be available to people that use drugs (Martins et al., 2017, Saleemi, Pennybaker, Wooldridge & Johnson, 2017).

Still, some critics have argued that these services, even when using highly advanced analytical techniques, might provide a false sense of security for users, because in reality the individual reaction each person has to a drug, pure or adulterated, cannot be anticipated by a testing a drug sample (Winstock, Wolff, & Ramsey, 2001). It is undeniable that a drug analysis cannot foresee an individual reaction, but when accessing relevant information on a product's content, a specialized technician can provide clients with scientifically based information of the most common reactions individuals have to a particular substance, increasing awareness of its potential risks. To fulfill one of drug checking services' main objectives, which is to accurately increase the user's awareness of risk, it is mandatory to have information. In the current scenario of chemical anarchy and with a high number of uninformed and unexperienced people using drugs, it is imperative, in our perspective, to offer people who use drugs the most accurate and science-based information available about effects, doses, routes of administration and other specific advice about their drug use.

Opponents frequently argue that not everyone comes to a drug checking service (Winstock, Wolff, & Ramsey, 2001). It is a fact that many people, for several different reasons, might not access this type of harm reduction intervention and it is fundamental to question if drug checking services are reaching those who need it most (Kealy & Webber, 1975). There is already an interesting body of research published on the limitations of harm reduction programs, raising very pertinent questions about their nature and objectives, particularly when adopted as a mainstream public health strategy (Barratt, Allen, & Lenton, 2014, Race, 2008; Moore, 2008, Roe, 2005, Young, 2000). All of these issues should be accounted for when designing projects in this field. However, the availability and access to health care is a basic human right for everyone, even for those who don't wish to use it and particularly to those who have difficulties accessing it. Certainly, drug checking is not a panacea to all risks related with drug use, but it can definitely mitigate many of them, for some people and that is something.

Concerning the criticisms around the lack of robust impact studies around this topic, although randomized controlled trials, the golden standard for program evaluation, have not yet been performed regarding drug checking services, there are some preliminary results that indicate the potential of drug checking in promoting behavior change (Valente et al., 2019; Measham, 2019; Day et al., 2018; Martins et al., 2017; BAONPS, 2017b; Sage & Michelow, 2016; Saleemi, Pennybaker, Wooldridge & Johnson, 2017, Michelow & Dowden, 2015; Wiese & Verthein, 2014, Ritter & Cameron, 2006; Johnston et al., 2006; Benschop et al., 2002). It is worth mentioning that randomized controlled trials are very difficult to conduct in the natural contexts where these services are implemented and the random selection of participants would raise ethical issues, particularly if the participants selected for the control group would eventually take a dangerous untested substance. Also, until recently there has been a lack of interest from universities and other agencies in funding research in this area, so the burden of proof for drug checking's efficacy has been on the civil society organizations that perform it, groups that usually don't have the expertise or the human and material resources to do a complete evaluation.

It is undeniable that more robust measures are required to fully access the impact of drug checking services, and that it is difficult to generalize the results of the studies performed so far to all drug checking services. However, there is a very interesting body of research, that cannot be overlooked, showing drug checking as a potential effective service to:

• Increase government and health workers' skill in responding to the constant changes in the drug market, namely by enhancing monitoring capacities: drug checking services have been able to detect and alert for the presence of NPS as adulterants of commonly consumed drugs, such as MDMA, amphetamine or LSD (Brunt et al., 2016; Giné, Espinosa, & Vilamala, 2014; Martins et al., 2017) as well as help track the nature and evolution of the NPS market and of drug markets in general (Giné et al., 2017), establishing it as a fundamental complement to other monitoring strategies such as police seizures and waste water analysis. Drug checking has also been a useful tool for obtaining information about drug adulteration in hard-to-reach markets, like cryptomarkets (Caudevilla et al., 2016; Quintana et al., 2017; van der Gouwe, Brunt, van Laar, & van der Pol, 2017). In most epidemiological studies, it is also an extremely relevant tool to complement the self-report information provided by people who use drugs, helping to understand the divergence between what people report they have used and what they actually take (Barratt & Ezard, 2016). The information from drug checking services can support forensic toxicologists and medical doctors in understanding drug markets and designing intervention protocols (Brandt, King, & Evans-Brown, 2014), and governmental and civil society organizations to better design prevention and harm reduction campaigns (Keijsers, Bossong, & Waarlo, 2008). There is evidence that a fringe of people, particularly young users in the beginning of their drug use career, who haven't had contact with any other drug counselling services are interested in drug checking (Hungerbuehler et al., 2011), which also corroborates its potential as an interesting harm reduction tool.


• Promote change in drug taking behaviors and practices: one of the main objectives of community-based drug checking services is to prevent users from taking dangerous and highly adulterated substances. Like many prevention interventions, drug checking aims at changing people's behaviors by providing them with accurate information about their drug content, and with specific strategies on how to minimize the risk drug using carries. Some authors suggest that non-problematic drug use appears to be related to users' self-control and self-imposed rules (Cruz, 2014; Fishbein & Ajzen, 2010). These concepts are based on the assumption that humans are rational in their decision-making and use the information available to them. The theory of reasoned action (Ajzen & Fishbein, 1980) and the theory of planned behavior (Ajzen, 1991) describe intention as the deliberate disposition to exercise effort to perform a certain behavior, and suggest that behavioral intention is an immediate determinant of actual behavior. Both these theories have extensive empirical validation that supports their usefulness in explaining a number of behaviors, namely drug use (Armitage & Conner, 2001), and they serve as an important theoretical base for several drug checking services. Studies focusing on the impact of drug checking on clients' behaviors show that most users report the intention of not using the substance when the result was unexpected and indicative of dangerous or unknown compounds (BAONPS, 2017b; Benschop et al., 2002; Martins et al., 2017; Michelow & Dowden, 2015; Sage & Michelow, 2016; Saleemi, Pennybaker, Wooldridge & Johnson, 2017, Wiese & Verthein, 2014). Recently Martins et al. (2017) presented data from Boom Festival in Portugal showing that after an alert was published at the festival warning patrons that DOx and 25x-Nbome were being sold as LSD, the number of people wanting to test their alleged LSD increased considerably, and their reported intention of not taking the substance when it wasn't LSD was greater than 70%. So, assuming that intention matches behavior, these results are an important indication that drug checking services have a very relevant impact on users behaviors', fulfilling their most relevant objective, promoting healthier behaviors.

Besides the criticisms that have been addressed, drug checking services face other obstacles to their full implementation. A country's legal framework is one of the main constraints drug checking services have been dealing with throughout the years and there are very different specifications depending on the country or region where one wishes to implement a project. Limits on handling and possession of illegal compounds represent a major obstacle. Prohibitionist countries do not allow people to handle or transport illegal substances without a hard-to-obtain governmental license, and usually harm reduction technicians working in drug checking services are not eligible to apply for it. However, through lobbying or via other strategies certain projects have been able to circumvent this type of limitation, namely through forging collaborations with laboratories or universities that hold special permits, or by searching for techniques that do not require the handling of substances or possession of analytical standards, such as colorimetric reagents, FTIR or RAMAN spectroscopy (BAONPS, 2017a; Harper, Powell, & Pijl).

However, even in countries where the legal framework is favorable to the existence of these services such as Portugal, where not only the possession and consumption of drugs is decriminalized but also a specific legal framework has been created to accommodate a series of harm reduction responses, including experimental drug checking services, there was no government-funded drug checking project running until April 2019. Decision makers and governmental institutions do not recognize drug checking as a priority for dealing with the current situation of drug markets and are not committed to financially supporting a drug analysis service. The Portuguese example clearly shows that policy reform is not enough to guarantee the full implementation of drug checking services; it is important to mobilize local decision makers and partners, promote advocacy initiatives, and, in general, raise awareness about drug checking as a public health response.

When looking back at the history of harm reduction responses, the majority, if not all, of these initiatives had to face numerous obstacles, namely the prejudice that they might work as promoters of drug use. Needle exchange programs or substitution treatments have endured the same process until being worldwide accepted as valuable and evidence-based health responses (Hedrich, 2010). Although initially there was lack of institutional commitment for the provision of clean consumption materials or accurate information about drugs, what happened with the introduction of needle exchange and harm reduction programs was a huge reduction of the transmission of blood-borne viruses in people that use drugs, establishing them as a cost effective and fundamental measure not only promoting the health of users but also of surrounding communities (Laufer, 2001; Strathdee & Vlahov, 2001).

The principle behind the advocacy for drug checking services is the same, as Barratt and Ritter (2017, p.101) noted, "We have the capacity to test and disseminate accurate information that could help people avoid harms and help health workers treat people more effectively. Do we really care more about deterring use of MDMA than we do about the safety of people who use it?". Isn't there a moral obligation to provide people with potentially life-saving information if we have the means to provide it? When it is known that people will inevitably buy and use drugs either within a repressive or more liberal legislative system (Quintas, 2011) and that production and distribution of those drugs will be carried out by people without the required knowledge and skills, with profit as a main driving force, what measures should be taken by a government that wants to protect its citizens? We, along with other authors and organizations have argued that the regulation of the production, supply and use of drugs should be the first approach to tackling most drug-related issues—not in a carefree and liberal way, but in a careful, sophisticated and restrained way, with control over products, vendors, outlets and where drugs can be consumed (Rolles, 2009). Although important enough to mention, the discussion of this argument is outside of the scope of this text. In the immediate impossibility of implementing these regulations, it makes sense to advocate for the adoption of pragmatic measures to protect people who use drugs. Providing drug analysis services to potential drug users who are forced to resort to the illegal market to get their drugs and providing infrastructure and resources that help them to take important decisions about their drug use with as much factual information as possible, seems to be one of the most sensible responses possible.

Drug checking has a history almost parallel to the war on drugs, and in the current legal framework the provision of integrated drug analysis harm reduction services targeted for people who use drugs can definitely be considered one of the best available tools to reduce harms and empower users to take informed decisions.