The most important facts in brief 

  • In 2019, synthetic cannabinoids were tested for the first time as an additive in
    cannabis flowers or hashish in various Swiss drug-checking services. 
  • Since the beginning of 2020, the Drug Information Centre of the City of Zurich (DIZ) has increasingly analysed cannabis samples that the users believed had been spiked with synthetic cannabinoids. 
  • Synthetic cannabinoids were found in more than half (50 out of 91) of the samples in the course of laboratory analyses. 
  • Synthetic cannabinoids are largely unexplored and are suspected of causing severe side effects and even death. 
  • The assessment that cannabis is a substance with a comparatively low risk of overdose has become obsolete since the emergence of synthetic cannabinoids. 
  • The DIZ advises all cannabis users to be cautious and to observe the safer-use rules when consuming. 
  • From 1 October 2020, a total of 10 cannabis samples can be handed in weekly at the DIZ. 

Initial situation

Since 2008, so-called synthetic cannabinoids have been circulating on the illicit drug market in Switzerland. Originally used as an additive in incense mixtures (e.g. "Spice"), they were mainly consumed by experienced users (so-called "psychonauts") out of interest in the effects. Synthetic cannabinoids cannot be detected in common urine tests, which is why these substances were also used by people who have to submit urine samples regularly. 

In 2019, synthetic cannabinoids were tested for the first time as additives on cannabis flowers or hashish in various Swiss drug-checking services. Since the beginning of 2020, enquiries and analyses on synthetic cannabinoids have been accumulating at the Zurich Drug Information Centre (DIZ) of the city of Zurich. The Zurich Forensic Institute has also noticed a significant increase in seizures since the end of 2019. Due to the limited capacities at the DIZ, currently (as of September 2020) around 10 people per week have to be turned away who want to hand in suspicious cannabis samples for analysis. Feedback from other drug-checking services in Europe and from the EMCDDA suggests that the increased occurrence of synthetic cannabinoids is a phenomenon that has so far mainly been observed in Switzerland. 

The term "synthetic cannabinoids 

The term "synthetic cannabinoids" has become internationally established for this group of substances. However, it is not clear-cut, because cannabinoids that are formed naturally in the hemp plant and have a significantly lower risk potential (THC and CBD) can also be produced synthetically. The group called synthetic cannabinoids is similar in its mechanism of action to THC, the psychoactive ingredient in cannabis. This group binds to the same receptors (CB1/CB2) as THC, but in some cases with more than 100 times stronger binding, which explains the significantly stronger effect. Synthetic cannabinoids thus imitate the effect of THC, but differ in their structure. Because of their mechanism of action, they are also called cannabimimetics (mimic = to imitate) or cannabinoid receptor agonists. 

91 substance samples submitted to the DIZ and analysed 

In the first eight months of 2020, the DIZ analysed 91 cannabis samples suspected of having been spiked with synthetic cannabinoids. The clients declared their sample before analysis as follows: 

  • 85 Dispensing of "conventional weed" (cannabis flowers with a content of more than 1% THC) 
  • 5 Duties of hashish 
  • 1 Dispensing of "legal weed" with a THC content of less than 1 % ("CBD weed") 

83 persons stated that they had bought the substance in private (among acquaintances, etc.). 6 persons bought cannabis "on the street", one person on the internet and one person at a party. 

Analysis results: Over 50 % of the samples spiked with synthetic cannabinoids 

Synthetic cannabinoids can only be determined by means of complex methods such as gas chromatography and mass spectrometry. The laboratory analysis of the 91 samples provided led to the following result: 

More than half of the samples (50) tested positive for synthetic cannabinoids. 

  • bei 48 Proben handelte es sich um «CBD-Gras» (THC < 1%) 
  • 1 sample had a THC content of over 1%. 
  • 1 sample showed both high CBD levels and high THC levels. 

The 50 samples that tested positive contained between 1 and 5 different synthetic cannabinoids. 34 samples contained 1 synthetic cannabinoid, 8 samples 2, in 7 samples 3 different synthetic cannabinoids were detected, one sample contained 5 different ones. Little is known about interactions and additional risks of mixed use of different synthetic cannabinoids. However, it can be assumed that the risks of consumption increase the more different synthetic cannabinoids are present. Most frequently (n=27), F-MDMB-PICA was detected in the analysis, which is suspected to be responsible for several deaths in Europe and North America. Little is known so far about the mode of action and toxicology of these and the other substances analysed (see graph). 

The various synthetic cannabinoids are only determined qualitatively in the laboratory (no quantitative measurements), which is why no statements can be made about potency. 

Synthetic cannabinoids analysed in the 50 samples according to frequency of occurrence. 

Symptoms after consumption 

The users reported to the DIZ because they had experienced serious side effects during use that had not been experienced before, such as palpitations, strong inner restlessness, panic attacks, disorientation, unconsciousness, hallucinations and unusual strong feelings of intoxication. These were mainly experienced as particularly intense in the first 10 to 30 minutes after use. Occasionally, clients had to seek emergency medical care due to the strong symptoms. 

Risk assessment 

Synthetic cannabinoids that are not declared as such can lead to risky overdoses and/or strong side effects that are often harmful to health. This effect is intensified by the sometimes uneven distribution5 of the substance on the flowers, which can lead to high concentrations. 

In contrast to naturally occurring THC, acute and severe poisoning is common with synthetic cannabinoids. Their use can lead to fainting, palpitations, high blood pressure, seizures, nausea with vomiting, loss of mental capacity, confusion, delusions, acute psychoses, craving for further use, aggressive and violent behaviour and even heart attacks. 

The high potency of synthetic cannabinoids increases the risk of overdose. In addition to their high potency, some synthetic cannabinoids have a particularly long degradation time of the substance (detectability) in the blood and can lead to a prolonged psychoactive effect. 

  • Have cannabis tested at a drug-checking service if suspected. 
  • When using newly purchased cannabis products for the first time, only "test" them (take two or three puffs) and then wait 20 minutes. If the effect is unusual, refrain from further use! 
  • Avoid mixed consumption! Mixed consumption (also with alcohol or medicines) is particularly risky because of the unpredictable and as yet unknown interactions. 
  • Mix cannabis products well before consumption (use a grinder) to avoid a strong concentration of possible synthetic cannabinoids on individual flower parts. Particular care should be taken with residual material that has fallen off the outer flower parts, as a particularly high concentration of synthetic cannabinoids is suspected in them. 


Only a laboratory analysis provides reliable information about the composition of cannabis. Synthetic cannabinoids cannot be detected visually. The price is also no indication that it could be a misdeclaration. Consumers named an average purchase price of CHF 10/g in the DIZ. This corresponds to the market prices for illegal, THC-rich weed. 

The assessment that cannabis is a substance with a comparatively low risk of overdose has become outdated since the emergence of synthetic cannabinoids. Especially if users are not aware that they are ingesting a much more potent substance than assumed (misdeclaration), there is a high risk of overdose. More than half of the suspicious samples tested in the DIZ contained one or more synthetic cannabinoids. In the other samples, the suspicion was not confirmed. This shows that also in cannabis use, set and setting can influence the experienced effect. 

Overall, the current development is worrying from the point of view of the DIZ and requires additional harm reduction measures. The DIZ is therefore expanding its offer: From October 2020, a total of 10 cannabis samples can be handed out weekly. The offer is anonymous and free of charge and includes, in addition to the substance analysis, an obligatory counselling interview with a specialist. The results of the cannabis drug checks are evaluated on an ongoing basis. 


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