Bulletin July 2019 Number 187

While we might be aware that so-called ‘legal highs’ are now the recreational drugs of choice for many, their impact on toxicology services is largely a hidden problem. This article explores their impact on drug testing strategies.

Definition of novel psychoactive substances and the law

The term novel psychoactive substances (NPS) encompasses several groups of different drugs, as illustrated in Table 1. These are grouped according to their effect, but not necessarily by similarities in their chemical structure. The term includes newly synthesised compounds, as well as older drugs that have only recently become widely available.
The United Nations Office on Drugs and Crime (UNODC) Early Warning Advisory on NPS reported that, in December 2018, there were up to 428 different NPS drugs available in the UK and North America. They also estimated that the numbers are still increasing, with one new substance becoming available per week.

While it should be acknowledged that many of the compounds identified by early warning systems might not become widely used, they still pose significant challenges in the field of toxicology worldwide. Early in this NPS epidemic, most new compounds were synthesised in China. However, more recent evidence suggests that production is shifting towards Europe, where there is the highest demand for these drugs.

On 26 May 2016, the Psychoactive Substances Act came into force in the UK. This took a different approach from previous drug legislation. It used a generic approach based upon the principles of chemical similarity to allow the legislation to cover a broader array of drugs, without naming them. This has allowed much greater flexibility in its application; however, the predicted reduction in the availability of NPS has notably not been evident.

Availability and use of NPS

The ready availability of NPS on the internet, the perceived higher quality of these compounds and reduced stigma associated with NPS use in comparison to more traditionally abused drugs, such as heroin, has made NPS the drugs of choice for many. This is compounded by the widely used former term for many drugs – ‘legal highs’ – which for many users gave a false impression of their safety and legitimacy. The internet is also used as an information exchange for users of NPS to share experiences of new compounds. So-called ‘psychonauts’ experiment with different drugs, drug combinations and doses to explore the boundaries of the drug-associated effects, often documenting their findings in great detail.

The patterns of abuse are also changing. The stereotypical drug abuser largely no longer exists. Most users are now multi-drug abusers, from very different backgrounds, which again makes use harder to identify. A trend that has emerged is the use of synthetic cannabinoid receptor agonists by the homeless and prisoners, which is becoming a significant problem for law enforcement and emergency departments across the UK.

NPS may be available in a variety of different forms, including powders, liquids, tablets, nasal sprays and even impregnated into book pages. This increases the challenge to law enforcement and in the investigation of deaths. The high potency of many NPS means that a low dose is used. This further increases the challenge in identifying these compounds as use is easy to conceal and importation is easier.

Identifying NPS in the toxicology laboratory

The rapidly changing trends in substance misuse makes identifying the compounds that an individual may have taken a complex but fascinating challenge. Traditionally, laboratories may have used a targeted screening panel to detect a defined range of compounds. Such panels typically included the compounds most commonly taken by substance misusers including opiates, cocaine and its metabolites, amphetamines, benzodiazepines and cannabinoids.

More recent screening panels have expanded the range of compounds detected to include compounds such as gabapentin, pregabalin, tramadol and oxycodone. However, these targeted screening approaches require the analyst to have a good idea of the compounds that are likely to be present in a sample prior to analysis. This makes them unsuitable for the detection of novel or uncommonly encountered substances such as NPS.

Targeted screening approaches may, therefore, be supplemented by untargeted screens, which are able to detect a wider range of compounds. Traditionally, these screening approaches used gas chromatography-mass spectrometry. However, liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) has now become the methodology of choice. The ability of LC-HRMS to detect the accurate mass of compounds in a biological sample to four decimal places provides a high degree of specificity for the detection of compounds. Using LC-HRMS, it may be possible to identify a compound that has been taken, using a combination of the measured accurate mass, the accurate mass of fragments detected following fragmentation of the compound of interest, the isotope pattern of the compound detected and the time taken for the compound to pass through the liquid chromatography portion of the system (the retention time). By comparing the parameters measured with a library of parameters collected from analysis of known compounds, the compound of interest can be identified. Laboratories are, therefore, heavily reliant upon the use of these libraries to identify novel compounds. Libraries must be accurate and kept up to date, with parameters collected from the analysis of pure compounds wherever possible.

Analysis of drug seizures, samples from living cases where the compound taken is known and the products of in vitro metabolism studies may also provide information. Close cooperation between laboratories and the publication of cases where novel or unusual compounds have been detected is vital if laboratories are to keep their libraries up to date. Worldwide databases are available that allow analysts to share intelligence on compounds that they encounter. Using this approach, the laboratory has an improved chance of identifying novel compounds in biological samples. However, measuring the concentration of such compounds requires a pure preparation of the compound that may not always be available. Thus, identifying a novel compound represents only half the battle.

Table 1: Novel psychoactive substance drug groups, common examples and their general effects

NPS group Common examples Effects
Aminoindanes MDAI, 5-IAI, ETAI Central nervous system (CNS) stimulants
Phencyclidine-type drugs Methoxetamine, eticyclidine, rolicyclidine Dissociatives, stimulants
Plant-based drugs Salvia divinorum, khat Varying
Phenethylamines 2C series, 4-FMA, 5-APB, benzodi-furans, PMMA Hallucinogens, stimulants
Piperazines BZP, TFMPP, MBZP CNS stimulants
Synthetic cannabinoid receptor agonists Spice (JWH-018), Black Mamba, AMB-FUBINACA, AMB-CHMICA, AKB-48, 5F-AMB and 5F-ADB Euphoria, dissociative
Synthetic cathinones Mephedrone, methylone, MDPV Stimulants, euphoria
Tryptamines MT, 5-MeO-DMT, AMT Hallucinogens

Other substances:

– novel opioids

– novel benzodiazepines


AH-7921, fentanyl analogues

Etizolam, diclazepam, pyrazolam


CNS depressants

Sedatives, hypnotics

NPS and the post mortem

Establishing the role of an NPS in post-mortem investigations is very challenging. There is very little data in the literature regarding the acute toxicity of most NPS. For some drugs, isolated case reports are available. However, multi-drug abuse is common and often measurement of the concentration of an individual compound has not been possible. This can make translating findings from case reports into routine toxicological practice difficult.

The vast majority of NPS have not been subjected to any form of pharmacokinetic study or formal assessment of their effects. This means that interpretation of concentrations might not be possible and any effects on driving, for example, have not been assessed. A feature of some drugs, such as gamma hydroxybutyrate (GHB), is the differing effects at different doses. GHB is used by some at low dose as a stimulant, but at higher doses as a sedative. The effect of dosing has not been studied for many NPS, which makes effects difficult to predict.

Chronic toxicity

Another challenge associated with NPS is the treatment of both addiction to such compounds and  any chronic toxic effects. Policymakers should ensure that NPS are included in substance misuse treatment strategies, which is even more difficult when their mechanism of action and best treatment approach may not be known. The novel nature of these compounds means that very little data are available on their chronic toxicity.

Similar to the now widely publicised association between ketamine use and bladder damage, and the risk of psychosis in users of highly potent cannabis strains, there is the potential of a ticking public health time bomb within large groups of individuals who may be at risk of long-term physical and mental health problems associated with NPS use.  
The use of NPS is a widespread and growing problem for society and science. It is clear that a multidisciplinary approach to this problem is essential and none more so than in the field of post-mortem toxicology. Here, the ability to detect drugs from this ever growing group is just one piece of the puzzle. The inability to measure very new drugs, along with a lack of knowledge of their potential toxic effects, hinders our ability to provide useful information. Therefore, working with histopathologists, coroners and law enforcement agencies in post-mortem investigations is key to understanding the role of NPS in sudden deaths.