An important factor in the health risks associated with Spice is the disparity of the mixtures with regard to the content of the active ingredients. Consequently, we do not know which dose of ‘Spice’ or JWH‐018 is typically used to achieve a desired high. Several studies reported that JWH‐018 is four to five times more potent than THC (Aung et al., 2000 ). Therefore, a JWH‐018 dose, four to five times smaller than common THC doses used in controlled studies, was expected to produce comparable effects. THC has repeatedly been administered in controlled experimental studies (e.g. Ramaekers et al., 2006a , 2016 ) in doses up to approximately 35 mg (500 μg·kg −1 bodyweight). In the current study, single doses of 2 and 3 mg JWH‐018 were administered. It was expected that a dose of 3 mg JWH‐018 would produce pharmacological effects comparable to a dose of 15 mg of THC. The latter has been shown to produce significant behavioural effects in controlled studies while keeping adverse events to a minimum (Ramaekers et al., 2006b ).

Two self‐experiments, describing the effects of JWH‐018, have been published. In one study, the researchers self‐administered Spice Diamond which contained JWH‐018 and the C8homologue of CP47,497 and reported cannabis‐like effects after 10 min. These effects slowly diminished over a period of 6 h (Auwärter et al., 2009 ). In the second study, two cannabis‐naïve volunteers smoked 50 μg·kg −1 JWH‐018 (resp. 3.6 and 4.3 mg per person) and reported typical cannabis‐like physical effects including thought disruptions (Teske et al., 2010 , Personal correspondence with the author).

Unfortunately, clinical trials assessing the effects of Spice objectively are lacking. Much of what we know is based on case reports or hospital admission reports, stating that its effects are similar but stronger than those of cannabis (Zimmermann et al., 2009 ; WHO, 2014 ). Adverse effects reported include tachycardia, agitation, hallucination, hypertension, minor elevation of blood glucose, vomiting, chest pain, seizures, anxiety, panic attacks and acute psychosis (Auwärter et al., 2009 ; Zimmermann et al., 2009 ; Sobolevsky et al., 2010 ; Every‐Palmer, 2011 ; Simmons et al., 2011 ; Hermanns‐Clausen et al., 2013 ; WHO, 2014 ). In most cases, these symptoms disappeared after a couple of hours (Harris and Brown, 2012 ).

Labels on Spice products often claim that they contain ‘natural’ psycho‐active material taken from a variety of plants. However, chemical analyses show that although it contains dried plant material, the active ingredients are synthetic (or designer) cannabinoid compounds ( http://www.drugabuse.gov/publications/drugfacts/spice‐synthetic‐marijuana ). In 2008, a German company reported the synthetic cannabinoid JWH‐018 as an active ingredient of Spice (Steup, 2008 ). JWH‐018 is one of the synthetic cannabinoids synthesized by J.W. Huffman, as part of research into cannabinoid receptor‐ligand binding (Wiley et al., 2011 ; Rosenbaum et al., 2012 ). It is an aminoalkylindole and produces cannabis‐like effects when smoked (WHO, 2014 ). Effects of JWH‐018 are evident after much lower doses than the typical THC dose (Ginsburg et al., 2012 ; Ford et al., 2017 ), and the side effects reported after JWH‐018 use are similar to the side effects associated with cannabis use (Rosenbaum et al., 2012 ). However, as JWH‐018 acts as a full CB 1 receptor agonist, it could lead to life‐threatening conditions such as, for example, seizures or convulsions (Havenon et al., 2011 ). In addition, the fact that the constitution of Spice products constantly changes with respect to active ingredients and dosages means that people can easily overdose and experience serious side effects (Sedefov et al., 2009 ; WHO, 2014 ). Due to these factors, from about 2008 quite a few countries have added several synthetic cannabinoids, including JWH‐018, to the list of controlled substances (Sedefov et al., 2009 ).

Recreational cannabis use is prohibited in most countries, and is one reason why potential users have turned to synthetic cannabinoids available on the market as legal highs. ‘Spice’ products were among the first herbal blends that were freely advertised over the internet. ‘Spice’ refers to a wide variety of herbal mixtures that produce experiences similar to cannabis. It is sold under many names, including Spice, K2, fake weed, Yucatan Fire, Skunk, Moon Rocks and others, and package labels often indicate that they are ‘not for human consumption’. Spice products have become very popular in several countries not only due to its easy access and portrayed safety but also due to the fact that they are not detectable in standard drug tests (Lindigkeit et al., 2009 ; Sedefov et al., 2009 ; Griffiths et al., 2010 ; Vardakou et al., 2010 ; Vandrey et al., 2012 ).

This questionnaire asks subjects to rate their liking and wanting of cannabis use during their present condition and in general. Subjects are asked four questions: how pleasant is using cannabis right now? How much do you want to use cannabis right now? How pleasant is using cannabis in general? How much do want to use cannabis in general? Subjective valence of liking and wanting is scored on a 5‐point scale: 1 = somewhat; 2 = slightly; 3 = moderately; 4 = very; and 5 = extremely.

The POMS is a self‐assessment mood questionnaire with 72 items, rated on a 5‐point Likert scale, with 0 being ‘not at all’ to 4 ‘extremely’. Subjects have to indicate to what extent these items were representative of their mood at that moment in time. Eight mood states are classified and quantified by calculating the sum score of associated items for each mood state, that is, anxiety, depression, anger, vigour, fatigue, confusion, friendliness and elation. Two composite scales are derived, arousal and positive mood (De Wit et al., 2002 ).

Ten black‐and‐white pictures are presented subsequently in 10 different locations on a computer screen. After presentation, each picture is presented alone with two possible locations where it appeared. Participants' task is to choose the correct location, a measure of immediate recall phase. This procedure is repeated six times with different stimuli and locations. After a 30 min delay, the recall phase is repeated; this test serves as a delayed recall measure (adapted from (Kessels et al., 1999 ).

The TOL is a decision‐making task that measures executive function and planning (Shallice, 1982 ). The task consists of computer‐generated images of begin and end arrangements of three coloured balls on three sticks. The subject's task is to determine as quickly as possible whether the end arrangement can be accomplished by ‘moving’ the balls in two to five steps from the beginning arrangement by pushing the corresponding number coded button. The total number of correct decisions is the main performance measure.

The SST measures motor impulsivity, which is defined as the inability to inhibit an activated or pre‐cued response leading to errors of commission. The current test is adapted from an earlier version (Fillmore et al., 2002 ) and has been validated for showing stimulant and sedative drug effects (Ramaekers and Kuypers, 2006 ). The task requires subjects to make quick responses to visual go signals and to inhibit their response if a subsequent visual stop signal, that is, ‘*’, appeared in one of the four corners of the screen. Dependent variables are go reaction time, stop reaction time, response accuracy, omission (not responding on go‐trials) and commission errors (not inhibiting a no go trial). Stop reaction time represents the estimated mean time required to inhibit a response. Stop reaction time is calculated by subtracting the stop signal delay from the reaction time on go‐trials associated with n‐th percentile of the reaction time distribution (Logan, 1994 ).

The DAT measures the ability to divide attention between two tasks performed simultaneously (Moskowitz, 1973 ). Subjects have to perform the same tracking task as described above but now at a constant level of difficulty. As a secondary task, the subject monitors 24 single digits which are presented in the corners of the computer screen. The subjects are instructed to react to the target number ‘2’ by removing their foot as fast as possible from a pedal switch. Mean absolute tracking error (in mm) and number of control losses are the performance measures of the primary task. Number of correct responses and mean reaction time (ms) of the responses to the target number are the performance measures in the secondary subtask.

The CTT measures the subject's ability to control a displayed error signal in a first‐order compensatory tracking task (Jex et al., 1966 ). Error is displayed as a horizontal deviation of a cursor from the midpoint on a horizontal, linear scale. Compensatory joystick movements null the error by returning the cursor to the midpoint. The frequency at which the subject loses control is the critical frequency or λ c . The test included five trials of which the lowest and the highest score were removed; the average of the remaining scores is taken as the final score.

An independent data safety monitoring board (DSMB) was installed to inspect and evaluate all vital, safety and behavioural data collected throughout the study. Data were submitted to the DSMB when the third and the last participant had completed an active dose condition. The study was continued only after a positive evaluation from the DSMB. The 3 mg dose condition was initiated after all subjects had successfully and safely completed the 2 mg dose condition.

Laboratory safety was determined at baseline and at the end of the test day. Blood and urine samples were used to perform haematology, clinical chemistry and urinalysis. Reference ranges were used to determine whether laboratory values were within the normal range. In case a measured parameter was outside the normal ranges, the medical supervisor decided whether or not it was considered a clinically significant deviation. In this decision, the other parameters, the overall condition of the participant and the baseline values were taken into account. At the end of the test day, participants were given a diary in which they were asked to take note of any possible side effect that they experienced up until 72 h after administration of the drug.

A Dyna‐Vision ambulatory patient monitoring system (Techmedic International, The Netherlands) was used to continuously measure and transmit ECG and vital signs in real time to the medical supervisor. The signal was transmitted to the laptop as well as the smartphone of the medical supervisor. A patch with sensors was attached to the subject's chest and connected to a receiver which was carried by the participant around his/her neck or middle. The system transmits three lead ECGs, saturation of peripheral oxygen, plethysmogram, respiration and skin temperature and beat‐to‐beat non‐invasive blood pressure. Alert signals were given every time one of the measures was above or below the normal range. The medical doctor would determine whether the value was clinically significant or not. The medical supervisor was present at the facility during the whole test day and could check on the participant whenever he/she experienced any complaints or when any of the ECG or vital sign measures indicated a value outside the normal range.

Test days took place at the testing facilities at Maastricht University. Participants would spend the day in a test room equipped with a bed, chair and table with laptop. The test room was adjacent to a bathroom and a room where the researchers were seated. Drug tests were performed upon arrival using a urine drug screen (assessing the presence of morphine, cocaine, cannabis, methamphetamine and amphetamine), and subsequently, an intravenous catheter was placed in the lower arm. Urine and blood samples were taken at baseline and at the end of the test day to determine laboratory safety (haematology, clinical chemistry and urinalysis). Oral fluid, blood and urine samples were taken at regular intervals during the test days to determine pharmacokinetics. Blood pressure and heart rate were measured at regular intervals during the test day using an Omron upper arm blood pressure monitor. Cognitive tests and subjective questionnaires were taken at regular intervals up until 12 h after administration (see Tables 1 and 2 ). In between test batteries, subjects could relax at the site, where they could watch TV, read or use the internet. Test days always started at the same time in the morning and were separated by a minimum wash‐out period of 7 days to avoid cross‐condition contamination (average of 37 days between test days, with a maximum of 92 days).

Prior to the first test day, subjects were trained extensively in all cognitive tests in order to become familiar with all tests and minimize practice effects. Subjects were not allowed to use alcohol or caffeine on the test day or the day prior to testing. Smoking was prohibited for 30 min prior to and during test days. Subjects were instructed to continue their cannabis use as normal but were requested to abstain from cannabis from about 5 days prior to the test day, to make sure they were negative on the test day. Subjects were asked to arrive at the site well rested. On each test day, subjects were instructed to have a standard breakfast before coming to the site. They received a lunch and dinner at the site.

JWH‐018 powder was mixed with a small amount of Knaster plant material and heated in a 10 cm glass pipe (‘crack pipe’). Glass pipes were only used once and replaced for every new administration. A 30 cm plastic tube was connected to the end of the pipe, while the bowl of the pipe contained the treatment. While the air holes were closed off, the bowl was heated for about 15 s. When the vapour was formed, the air holes were opened and the subject was instructed to immediately inhale the vapour in one take via the plastic tube. Drug preparation and administration was done by a different researcher from the ones performing the drug tests.

The study was conducted according to a placebo‐controlled, single‐blind, within‐subjects design and was performed in healthy, regular users of cannabis. On separate test days, each subject inhaled the vapour of a placebo, 2 and 3 mg of JWH‐018. An escalating dosing scheme was used, making sure that no subject received the high dose of JWH‐018 before having received the low dose. Subjects were quasi randomly assigned to receive one of the following treatment orders: 0–2–3 mg; 2–0–3 mg; or 2–3–0 mg.

A total of seven occasional users of cannabis were recruited via advertisements placed around Maastricht University. Participants were screened using a health questionnaire and underwent a medical examination (including an ECG, haematology and blood chemistry, urinalysis and drug and pregnancy screening). The following inclusion criteria applied to participants: occasional use of cannabis (minimal 1 year experience, with a minimum and maximum use of 24 and 104 times a year); free‐from psychotropic medication; good physical health as determined by medical examination and laboratory analysis; absence of any major medical, endocrine and neurological conditions; body mass index (weight/length 2 ) between 18 and 28 kg·m −2 ; and written informed consent. Exclusion criteria were as follows: history of drug abuse (excluding cannabis) as assessed by drug urine screens and questionnaires; excessive drinking (consumption of >20 alcoholic units a week); pregnancy or lactation or failure to use contraceptives; hypertension (diastolic > 90 mmHg; systolic > 140 mmHg); and history of psychiatric disorders.

The study was approved by the standing Medical Ethics Committee of Maastricht University and was carried out in compliance with the current revision of the Declaration of Helsinki (amended in 2013, Fortaleza) and the International Conference on Harmonization guidelines for Good Clinical Practice. A permit for obtaining, storing and administering JWH‐018 was obtained from the Dutch drug enforcement administration. All subjects gave written informed consent and received financial compensation for their participation.

Profile of mood states were taken at baseline and repeated four times after drug administration. Separate paired sample t ‐tests showed that subjects reported more fatigue after the high dose compared to placebo at 5 and 12 h after administration (M = −1.33; t 5 = −2.39; P = 0.031 and M = −1, t 5 = 5; P = 0.020) (see Figure 3 A). They also reported more fatigue after the high dose compared to the low dose at 12 h after drug intake (M = −1.4;t 5 = 2.746 P = 0.026) (see Figure 3 B). Arousal was reported to be higher 12 h after administration, after a low dose of JWH‐018, compared to placebo (M = −3.6; t 5 = 2.794; P = 0.025) and the high dose (M = 4.8; t 5 = 5.58 P = 0.0025).

Mean pharmacokinetics for JHW‐018 after administration of 2 and 3 mg doses is given in Figure 1 . A detailed report on the pharmacokinetics of this study has been published elsewhere (Toennes et al., 2017 ). In short, there was no clear dose–concentration relationship across the 2 and 3 mg doses. Overall, drug concentrations reached their maximum 0.08 h after inhalation and were lower after the 3 mg dose as compared to the 2 mg dose. Analysis of the residuals in the inhalation devices revealed that a substantial proportion (sometimes up to 70%) of the doses was not inhaled (Toennes et al., 2017 ).

Although subjects were instructed to abstain from cannabis as of 5 days prior to each test day, two subjects tested positive for THC on the drug test taken at baseline. Baseline measurements showed that these participants had 2.1 and 0.51 ng·mL −1 THC in serum, which indicates that last use of cannabis was probably a couple of hours or days before the start of the test day. THC concentrations below 2 ng·mL −1 are not associated with psychomotor impairment (Ramaekers et al., 2009 ). This indicates that psychoactive effects of THC were negligible at the start of the test day, which was indeed confirmed by the baseline subjective high scores of these participants.

Discussion

The current study is the first controlled clinical trial with the synthetic cannabinoid JWH‐018. We selected JWH‐018 as it is one of first psychoactive substances that was found in the popular Spice products. Though JWH‐018 has largely been replaced by a host of other synthetic cannabinoids since its introduction, it never fully disappeared from the market. Traces of JWH‐018 are still regularly found in products containing synthetic cannabinoids (Musshoff et al., 2014; WHO, 2014). Thus, the long‐standing history of JWH‐018 was one of the main reasons to select this compound for a phase 1 evaluation rather than any other synthetic cannabinoids. In addition, JWH‐018 is one of the few synthetic cannabinoids for which animal toxicology and receptor potency data were available prior to this trial (Aung et al., 2000; Atwood et al., 2010; Ginsburg et al., 2012; Wiebelhaus et al., 2012; WHO, 2014). Given that typical doses of JWH‐018 taken for recreational use are unknown, we estimated relevant doses of JWH‐018 that were minimally active on such toxicology and potency data.

The administration doses of of 2 and 3 mg JWH‐018 produced relatively low concentrations of this drug in serum. Concentrations of metabolites, of which some have been found to have CB 1 receptor activity (Brents et al., 2011), were also low (Toennes et al., 2017). Drug concentrations were certainly lower than some of those that have been reported in actual case reports (Hermanns‐Clausen et al., 2013; WHO, 2014). However, concentrations in case reports are probably higher, as these often come from people who have overdosed with the drug. Nevertheless, the current low concentrations were partly caused by suboptimal delivery of JWH‐018 with the glass crack pipe. This could be due to differences in puff volume (Azorlosa et al., 1995) or active substance escaping the smoking device. Analyses of the delivery devices, however, revealed the presence of substantial amounts of residual JWH‐018. This demonstrates that subjects did not inhale the full amount of the JWH‐018 doses. Administration of both doses of JWH‐018 was done in the same way, and subjects were given the same instructions. Pure JWH‐018 was mixed in a glass pipe with some Knaster and heated for about 15 s. The resulting smoke was inhaled in one take. Nevertheless, the residues in the pipes indicated that a considerable amount of the active substance was not inhaled. As this was a post hoc analysis, we unfortunately have no way of knowing whether this was more the case for the high dose than the low dose (Toennes et al., 2017). However, it may very well explain why drug concentrations were lower in the 3 mg dose as compared to the 2 mg dose condition. It can therefore be concluded that our method of administration might not have been optimal for administering the JWH‐018 powder. However, when users are smoking herbal mixtures of JWH‐018, a considerable amount of the psychoactive substance probably goes up in smoke as well. In fact, the maximum concentrations measured in the current study are very comparable with the concentrations found in subjects who smoked a similar dose of JWH‐018 in an herbal mixture in an earlier study (Teske et al., 2010; Kacinko et al., 2011). Yet, as stated before, higher concentrations have also been reported in hospital cases (WHO, 2014).

In terms of vital signs, low concentrations of JWH‐018 were well tolerated by the subjects. ECG, vital signs and laboratory safety measures did not show any clinically significant deviations from the normal ranges. Side effects after JWH‐018 administration were limited to one report of headache and two of tiredness/low energy. Subjects did report subjective feelings of high for 2 h after JWH‐018 administration, particularly in the low dose condition. This confirms that drug concentrations in the low dose condition were high enough to elicit a behavioural response. Yet maximal levels of subjective high were only half of those that have typically been reported in controlled cannabis trials in our lab (Ramaekers et al., 2009, 2016). Likewise, the duration of subjective high has been two or three times longer in previous studies with cannabis (Ramaekers et al., 2009, 2016). Other subjective evaluations only revealed incidental elevations in fatigue and arousal after JWH‐018 administration. This indicates once again that JWH‐concentrations in the current study may have been too low to produce a stronger subjective or physiological response that one would typically expect after a recreational dose of cannabis.

Despite the low serum concentrations, JWH‐018 did cause behavioural impairments. JWH‐018 impaired motor performance (CTT), divided attention (DAT) and response inhibition (SST), particularly after the 2 mg dose. Executive functioning (TOL), spatial memory (SMT), speed and information processing (DSST) were not affected by JWH‐018. This demonstrates that the JWH‐018 concentrations in the current study are about the minimum levels that are needed to produce behavioural impairment. Overall, however, impairments were relatively mild and present in a subsample of neurocognitive functions which are usually impaired after regular doses of cannabis (Fried et al., 2005; Ranganathan and D'souza, 2006; Ramaekers et al., 2006a,b, 2009). The behavioural data therefore also indicate that higher doses of JWH‐018 would be needed to achieve a behavioural impairment profile that is similar to a typical cannabis dose.

Preclinical studies have shown that JWH‐018, inhaled or injected, demonstrates potent THC‐like effects in mice. These effects include hypothermia, locomotor suppression, analgesia and antinociception (Brents et al., 2011; Wiley et al., 2012; Marshell et al., 2014; Vigolo et al., 2015). However, comparing preclinical data with the current results is tricky, as dosages administered to animals are not easily translated to doses used in humans. Using an inter species dose scaling, Ossato et al. (2015), demonstrated that side effects such as convulsions, myoclonia and hyperreflexia were only evident in mice after doses which are comparable to 0.5 mg·kg−1 in humans. Low doses, which are comparable to doses between 0.0008 and 0.08 mg·kg−1 in humans, impaired motor functioning and working memory in mice (Ossato et al., 2015; Barbieri et al., 2016). These effects of low doses of JWH‐018 are somewhat comparable to the results we show in humans. The doses used in the current study are within the latter range (2 and 3 mg equals approximately 0.03 and 0.04 mg·kg−1), but as already discussed, the actual dose that was inhaled was much lower due to suboptimal delivery of the drug.

The current study was the very first attempt to assess physiological, subjective and behavioural effects of JWH‐018 in a placebo controlled study in humans. As this was a first‐in‐man study, the number of participants included was kept to a minimum. Larger sample studies are needed to better define health risk profiles of synthetic cannabinoids and novel psychoactive substances (NPS) in general. EMCDDA (2009) guidelines recommend that individual health risks of NPS should be directly assessed in pharmacological studies in humans and animals as a function of a number of key risk variables such as dose and frequency of use (EMCDDA, 2009). Human studies should furthermore include psychological and behavioural measures. Moreover, the EMCDDA guidelines also advise to assess the risk of novel NPS relative to traditional drugs of abuse. Yet, to date, systematic toxicological and pharmacological studies with NPS in humans and animals are virtually missing which hampers full scale evaluation of NPS risk, also in relation to scheduled drugs. As a consequence, current science is lagging behind in providing reliable and well‐validated information on individual health risks of NPS that are badly needed to provide a full‐scale risk assessment according to EMCDDA guidelines. The present study clearly demonstrates that controlled studies with NPS in humans are feasible and can be carried out safely in a phase 1 setting. The present study design therefore can serve as a blueprint for follow‐up research with other NPS and with higher doses/concentrations of JWH‐018. Phase 1 trials are particularly useful for NPS for which typical user doses are unknown, and dose‐finding is needed in the laboratory as in the present case. Previous controlled studies with mephedrone, another classical NPS, have also demonstrated that phase 1 trials significantly contribute to drug and risk profiling of NPS (de Sousa Fernandes Perna et al., 2016; Papaseit et al., 2016).

In summary, JWH‐018 dosing in the present study resulted in drug concentrations that were generally low and not fully representative of common use. Yet initial impairments of neurocognitive function and subjective feelings of high did emerge despite the low levels of JWH‐018 in serum. The administration of higher doses is needed to obtain a more representative risk profile of JWH‐018. The phase 1 approach for evaluating risk profiles of synthetic cannabinoids can serve as a blueprint for future research.