The epicenter of fentanyl use in Mexico has been in Tijuana and Mexicali, two cities on the U.S. border characterized by drug use (Rafful et al., 2015; Goodman-Meza et al., 2022). In recent years, these cities have seen the largest seizures of fentanyl in the country (Comisión Nacional de Salud Mental y Adicciones, 2024a) as well as the exponential growth of its use and that of other adulterants such as xylazine.

Fentanyl is a much more potent synthetic opioid agonist than morphine and heroin, used for pain management in medical settings. Its illegal production in clandestine laboratories in liquid, pill or powder form has created a major opioid crisis in the United States, causing over 80,000 overdose deaths in 2023 (National Center for Health Statistics, 2023).

Xylazine is a non-opioid analgesic and sedative approved for veterinary use only. People exposed to this substance can develop skin abscesses and physiological dependence, present with symptoms compatible with a substance use disorder and experience severe withdrawal symptoms (such as irritability, anxiety, and dysphoria) after its abrupt discontinuation (Gupta et al., 2023). Its use has been detected in the United States, Puerto Rico, and the United Kingdom, with Mexico recently joining the list (Comisión Nacional de Salud Mental y Adicciones, 2024b).

The combination of the two substances has been recognized as a serious threat to human health and health alerts have been issued in the countries affected, together with recommendations to adjust medical treatments, implement harm reduction strategies and address health emergencies resulting from overdoses (Zhu et al., 2023).

In Mexico, the consequences of the modification of the drug supply, which has shifted from the use of heroin to fentanyl with xylazine, have been devastating for the most vulnerable communities on the northern border, Persons Who Inject Drugs (PWID), among whom overdose mortality has the greatest impact (Friedman et al., 2022).

In recent years, the Ramón de la Fuente Muñiz National Institute of Psychiatry (INPRFM), together with the Prevencasa, Programa Compañeros and Verter NGOs, the National Autonomous University of Mexico, the Tijuana Institute of Technology, the Center for Research and Advanced Studies and the Autonomous University of Baja California have monitored changes in the drug market, health consequences and the lived experience of people in Tijuana, San Luis Río Colorado, Mexicali and Ciudad Juárez:

• 2018. PWID mainly used black tar heroin, known as chiva in Mexican Spanish, without knowing it was heroin. They felt that the effects of white powder heroin, known as china white, were stronger. They got hooked more quickly¹ and experienced more overdoses. The main method for reversing an overdose was injecting salt and water. Only 1.6% had used naloxone² out of 600 people interviewed at rehab centers, where 2.7% had HIV and 80% HCV³ (Fleiz-Bautista et al., 2019).

• 2020. For the first time, we found heroin adulterated with fentanyl through the technique known as drug checking. Using immunoassay test strips to analyze the contents of eighty samples of white powder heroin residue in used syringes, we found that 93% of all the white powder samples contained fentanyl and that the population was being exposed to opioids without realizing it and without access to naloxone (Fleiz et al., 2020).

• 2023. For the first time, we detected the presenceof xylazine in 20% of the 300 samples of heroinand fentanyl analyzed using mass spectroscopy.This same year we also found a rapid increase infentanyl use, seven out of ten samples containedthis opioid, polydrug use with methamphetamines,coupled with overdoses, which the populationunsuccessfully tried to reverse with water andsalt, and an increase in the HIV index from 4.5%to 11% among PWID who used fentanyl and/ormethamphetamines and the development of skinabscesses that were more difficult to cure.⁴

These results revealed a complex, challenging reality:fentanyl consumption spread rapidly along the northernborder, like no other adulterant or psychoactive substanceever recorded in Mexico and showed how xylazine contributedto this health crisis shared with the United States.

Several factors have played a crucial role in this growingtrend: a porous border, the high availability on the streetsof the combination of these two substances, the low costof a dose (less than two dollars), the enhanced effects ofwell-being and relaxation that the population quickly identified,the social inequality that encourages these substancesto reach the most vulnerable people, thereby exacerbatingdisparities in health, housing, food and education, stigma (Volkow, 2020) and social pain associated with the “psychologicaldistancing from other people or social groups,”processed in parts of the brain that handle negative emotionalcomponents and physical pain (Zhang et al., 2019), increasing the need to use substances

The presence and production of fentanyl in Mexicohas been a topic of intense debate that has focused on thesubstance rather than the people and context. The scientificevidence is overwhelming: fentanyl and xylazine, aswell as their health consequences, are a worrying realityin a country that has created more unresolved controversiesthan actions, such as the failed attempts to declassifynaloxone in the General Health Law, the uninterrupted support for harm reduction programs, the limited availabilityof drug-assisted therapies such as methadone that was temporarilyunavailable, and the emotional pain of people thatwent unheard..

It is urgently required to address the perceived needsof PWID demanding access to a dignified life, which couldrepresent a hopeful sign for the reconstruction of peace processesin a region affected by insecurity, violence, and forpeople’s suffering.