Nitazens in Spain. Current situation as of May 2025.

In Episteme Social, the emergence of nitazens in Europe took us by surprise while researching fentanyl. This research culminated in the report “Fentanyl in Spain. Evidence, perceptions, and realities.” The study’s findings led us to hypothesize that, in Europe, and by extension Spain, a public health crisis caused by nitazens was more likely than one caused by fentanyls. The main reason is that it was easier to buy nitazenos than fentanyl on the dark web (Martínez Oró: 2024 66-78). This hypothesis encouraged us to apply for funding from the Government Delegation for the National Plan on Drugs, in the 2024 call for grants to NGOs for supra-community programs on addiction. The aim was to carry out a study to assess the threat posed by nitazens in Spain. The main product is the report entitled “From fentanyls to nitazenos. Study of the threat posed by nitazens in Spain.” Available here (link).

Benzimidazole opioids, also called nitazens, are a class of synthetic opioids with a benzimidazole structure. They were first synthesized in the 1950s by CIBA Pharmaceuticals when it was looking for alternatives to morphine. Nitazens are selective µ (mu) opioid receptor agonists. Broadly speaking, they can be up to several hundred times more potent than morphine. Their potency means that they are compared to fentanyl, although they have no structural relationship. They have never been used in clinical medicine due to their considerable risk of overdose. This makes it impossible, unlike fentanyls, for drugs to be diverted to informal markets.

The main objective of our study is to “analyze the threat posed by nitazens to Spain.” After conducting an exhaustive review of the scientific and gray literature and interviewing eighteen professionals, we can conclude that a health crisis caused by nitazens is even more likely than one caused by fentanyls. The main reason is that large criminal gangs have no interest in synthetic opioids, including nitazenos, because consumers demand heroin. Heroin stocks in Afghanistan, although lower than in previous years, are sufficient to supply European markets. This does not prevent the possibility that, in Spain, as in other countries in Europe, there may be an outbreak of overdoses resulting from the adulteration of certain drugs with nitazens. So far, Spain has been free of any health emergency caused by nitazens. However, this does not mean that these synthetic opioids cannot appear at any time as a result of their availability on the dark web.

From 2021, but especially from 2023 onwards, in different parts of Europe, following various outbreaks of overdoses among heroin users, nitazenos burst onto the drug policy scene in an unprecedented manner. From that moment on, outbreaks of overdoses in multiple locations across Europe, with no apparent connection, became frequent. At that time, national and international agencies were keeping a close eye on fentanyl and its analogues. The opioid crisis in the United States, with nearly a million deaths, justified this. The emergence of nitazens as an adulterant in low-quality heroin shipments or fake drugs represented a new threat to public health and a new challenge for addiction managers and professionals.

In different parts of Europe, such as the United Kingdom and Ireland, mid- and low-level dealers in the distribution chain have access to very low-quality heroin. In order to improve its potency, they came up with the idea of buying nitazens on the dark web. The aim was to use them as adulterants to obtain heroin that was, in theory, of higher quality. The results of this strategy have been disastrous, causing outbreaks of overdoses and the associated deaths. In addition, consumers demand heroin, and the effects of nitazens, apart from a few rare cases, are despised both for their effects and for the low safety margin they offer. Therefore, the detection of nitazens in Spain, for the time being, can only be the result of a dealer who, with the bizarre idea of making heroin more potent, ends up causing dozens of overdoses.

In short, the threat posed by nitazens to Spanish public health in May 2025 is relatively low. The main threat to Spain is that a small-scale trafficker could adulterate a batch of heroin with nitazens. At the moment, we have no evidence of this happening. And this scenario seems remote, given the events that have taken place in Europe and the fact that we have no previous experience with fentanyls. We must maintain surveillance systems to be able to respond to its hypothetical emergence. Furthermore, some resources, in a more or less formal manner, have been equipped with protocols to deal, in the first instance, with fentanyl overdoses and, in recent months, with nitazens. Once again, as in any study on the threat of a drug carried out in Spain, it is clear that Spain has an excellent addiction care network. If nitazens were to arrive, there is no doubt that outbreaks of overdoses, especially fatal ones, would have less impact than in other European countries.

Nitazens have attracted a great deal of professional attention due to their dangerous nature. Nitazens have caused outbreaks of overdoses in several European countries. In Spain, there have been no outbreaks of overdoses or deaths associated with nitazens to date. We therefore conclude that the threat posed by nitazens in Spain is relatively low, for the following four reasons.

Firstly, some voices have suggested that, given the shortage of Afghan heroin, nitazens, in the absence of fentanyls, would be the synthetic opioids called upon to fill the market niche. Afghan heroin continues to supply European drug markets. In 2024, the harvest increased by 20% compared to 2023. And if Afghanistan were to stop supplying Europe with heroin, other countries such as Myanmar and Pakistan would become the main producers. As long as heroin is available on the Spanish market, the vast majority of opioid users will reject the idea of experimenting with synthetic opioids. For the time being, the supply of heroin in Spain remains stable and there are no signs that it will disappear.

The second. In Europe, nitazens have been used as an adulterant, especially in heroin and fake benzodiazepine pills and other drugs. In Spain, we currently have no evidence of heroin or other drugs being adulterated with nitazens. Adulteration of heroin with nitazenos is more likely, but it is almost impossible for us to detect nitazens in fake drugs because there is no demand, and therefore no market, for fake drugs. This situation allows us to be relatively optimistic. Spain has not yet experienced any outbreaks of overdoses. In view of developments in Europe, where overdoses involving nitazenos are becoming less frequent, we can cautiously state that the risk of an outbreak of overdoses involving nitazens in Spain is becoming less likely.

The third. In Europe, during these months of 2025, outbreaks of nitazens overdoses have decreased. Our hypothesis is that low-level traffickers are abandoning nitazens as adulterants. Overdoses are too recurrent, which attracts the attention of law enforcement authorities. Therefore, nitazenos have proven to be unsatisfactory as adulterants for other drugs. This situation allows us to hypothesize that, in the coming year, nitazens could lose a significant presence in European drug markets. Such a situation would encourage, if it has not already done so, Chinese chemists to seek a functional alternative to continue supplying European drug markets. Nitazens emerged as an alternative to fentanyls, but in view of their abuses, it seems clear that they have not fulfilled their purpose. It is therefore to be expected that the Chinese industry will bring new drugs onto the dark web market, whether or not they belong to the synthetic opioid family. There are still five families of synthetic opioids to be explored as drugs of abuse.

The fourth and final reason, although in our opinion the most important, is that if nitazens were to become a reality, the powerful Spanish addiction treatment network could offer effective, efficient, and high-quality responses to the threat. Opioid substitution treatments with methadone and buprenorphine, the availability of naloxone in different forms, highly qualified professionals, and a network of resources distributed throughout the country are the best guarantee against any threat from synthetic opioids or any other substance. The number of overdoses is the key indicator for confirming that Spain is free of nitazens. Overdoses will become irrefutable evidence when users consume heroin adulterated with nitazens. For the time being, the number of overdoses remains stable.

In short, nitazens appeared as an alternative to fentanyls. But it is clear that this is a family of synthetic opioids that is far too dangerous. Its narrow safety margin between active and lethal doses means that low-level traffickers dismiss it as a drug adulterant. In short, we conclude that nitazens will gradually lose their presence as an adulterant in controlled drugs. At least as an adulterant in heroin, which, in the case of Spain, is much more likely than counterfeit pills containing nitaz