(This is just another outcome of Harm Reduction Only Ideology – The ever-increasing permission models that enable and EQUIP (like Needle Distribution Programs) ongoing drug use isn’t seeing drug use and its intensity reducing, only increasing. This is not only bad policy practice, it is contrary to all the aims of national and international drug policy intents – Welcome to drug use normalisation 101)
A recent national study has revealed serious health consequences tied to a practice many people underestimate. The National Drug and Alcohol Research Centre at UNSW Sydney published the research in January 2026. It examined the co-injection of drugs among people who regularly inject substances across Australia. The findings show just how widespread this behaviour has become, and who faces the greatest risk.
What Is Co-Injection of Drugs?
Co-injection means mixing two or more drugs inside a single syringe before injecting them. This differs from using multiple substances on the same day. With co-injection, the body receives everything at once, in the same dose. That simultaneous intake puts the body under serious pressure. It must process several substances at the same time, with no ability to manage the combined effects.
The 2025 Illicit Drug Reporting System (IDRS) surveyed 865 people across all Australian capital cities. The study found that 18% of participants had combined two or more drugs in the same syringe within the month before their interview. Most of them did this more than once. For a significant number of people, co-injection is not a one-off event but a repeated pattern.
The Most Common Drug Combinations
Among those combining drugs in the same syringe, the top combination was methamphetamine crystal mixed with heroin. This makes sense given the data. Opioids and stimulants already rank as the two most commonly injected drug classes in Australia. Research from Melbourne between 2017 and 2019 confirmed a similar trend. Studies in Seattle also recorded a sharp rise in the co-use of methamphetamine and opioids over the same period.
The data also picked up diphenhydramine, an antihistamine with sedative effects sometimes found in over-the-counter sleep capsules. GHB, ketamine, and various pharmaceutical stimulants showed up as well. Of those who combined drugs in the same syringe, 84% mixed two substances. Around 13% used three drugs at once.
Who Is Most Likely to Co-Inject?
The study linked several factors to a higher likelihood of co-injection of drugs. Men reported this practice at notably higher rates. Daily injectors stood out too. They held roughly four times the odds of combining substances in a single syringe compared to those who injected less often.
Needle sharing played a significant role as well. People who shared syringes in the past month were more than twice as likely to have co-injected. Researchers also identified “bingeing” as a key risk factor. Bingeing means using drugs continuously for 48 hours or more without sleep. Those who had binged were around four times more likely to combine substances in one syringe. Together, these patterns show that co-injection tends to cluster among people with the most intense and high-risk drug use habits.
Why Co-Injection of Drugs Is So Dangerous
Mixing stimulants and opioids in the same syringe puts major strain on the cardiovascular and respiratory systems. When someone takes two substances at different times, the body can begin to clear one before the other arrives. Co-injection removes that buffer entirely. A stimulant pushes the heart rate up and sharpens alertness. At the same time, an opioid suppresses breathing and slows the central nervous system. That direct conflict between the two substances makes certain combinations deeply unpredictable and potentially fatal.
Earlier studies connected the co-injection of methamphetamine and opioids to poorer physical and mental health outcomes over time. They also flagged an elevated risk of overdose. The 2025 IDRS data tell a similar story. The behaviour clusters tightly around other high-risk patterns, especially daily use and binge episodes. Both of those patterns carry their own serious long-term health consequences.
Understanding the Bigger Picture
Co-injection of drugs is not a fringe activity. A meaningful number of regular injectors in Australia engage in it. It tends to happen among people whose drug use is already the most intense. The mix of stimulants and opioids in a single syringe represents one of the more dangerous forms of polydrug use seen in the country today. The health consequences, both immediate and long-term, need far greater public awareness.
Drug use patterns keep shifting across Australia. The risks tied to co-injection of drugs will stay relevant as long as that shift continues. Understanding exactly what people put into their bodies, and how, stays critical. The 2025 IDRS data give us a national snapshot. It is both timely and relevant, not only for researchers and clinicians, but for anyone who cares about public health.
(Source: WRD News)