No Evidence of Interactive Effects of Oxytocin and Naltrexone on Social Gaze in Autism: A Naturalistic Eye Tracking Study

Human connection relies on a silent, rapid exchange of signals. We read faces, interpret tones, and gauge intentions to navigate the social world. Among these signals, eye contact holds a unique power; it signals attention, trust, and a willingness to engage. For many people, looking someone in the eye is a natural, almost automatic part of conversation. For others, particularly those with autism spectrum disorder, this same act can feel overwhelming or confusing, leading them to look away. Scientists have long suspected that the brain's chemical systems play a major role in how we manage these social cues. Two specific chemical systems have drawn significant attention: one involving oxytocin, a hormone often linked to bonding and trust, and another involving the body's natural opioids, which help regulate how rewarding social interactions feel. While animal studies have suggested that these two systems might work together to influence how much an animal looks at another, it has remained unclear whether this partnership exists in humans, and whether tweaking these chemicals could help people with autism feel more comfortable making eye contact.

To investigate this, a team of researchers at the University of Vienna and MedUni Wien set up a unique experiment involving seventy-three adults. Thirty-four of these participants had been diagnosed with autism spectrum disorder, while the others were neurotypical controls. The study was designed as a series of four separate visits for each person. During each visit, the participants received a different combination of treatments in a double-blind fashion, meaning neither they nor the researchers knew which treatment was being given at the time. The treatments included a dose of oxytocin delivered through a nebulizer, a dose of naltrexone taken as a pill, both drugs together, or a placebo that looked and tasted the same but contained no active medicine. Naltrexone is a medication that blocks the brain's opioid receptors, while oxytocin is the hormone associated with social connection. The researchers chose a dose of fifty milligrams for the naltrexone and ten international units for the oxytocin, timing the administration so the drugs would be at their peak strength during the main part of the experiment.

The core of the experiment was a naturalistic face-to-face conversation. Each participant sat down for a seven-to-ten-minute semi-structured interview with a researcher of the same sex. While they talked, the participants wore a mobile eye-tracking headset that recorded exactly where their eyes were looking. The researchers were interested in whether the participants looked at the interviewer's eyes, mouth, or face in general, or if they looked away at the background. They also collected saliva samples at three points during the session to measure cortisol, a hormone that indicates stress levels and the activity of the body's stress response system. This allowed the team to see if the drugs were actually working inside the body, even if they didn't change how people looked at each other.

The results of the study offered a clear picture of how these participants interacted, but they did not confirm the researchers' initial hopes. The study found that, on average, adults with autism did display different gaze patterns compared to the neurotypical group, but the difference was not a simple lack of eye contact. Instead, the most noticeable difference was that the participants with autism, particularly the women in the group, spent more time looking at the background of the room rather than the person they were talking to. This pattern was consistent throughout the interview, suggesting it was a stable way of managing the interaction rather than a momentary lapse. However, when the researchers looked at the effects of the medication, the story changed. Neither oxytocin, naltrexone, nor the combination of the two had any measurable effect on where the participants looked. The drugs did not increase eye contact, nor did they reduce the tendency to look at the background. The hypothesis that combining these two chemicals would produce a stronger effect on social attention was not supported by the data.

While the drugs did not change the gaze behavior, the study did confirm that the medications were biologically active. The participants who received naltrexone showed a reliable increase in cortisol levels during the session, indicating that the drug successfully engaged the body's stress response system. This finding is important because it proves that the lack of change in eye contact was not due to the drugs failing to work inside the body. Instead, it suggests that the complex behavior of looking at someone during a conversation is not easily shifted by a single dose of these chemicals, even in a controlled setting. The study also highlighted a significant difference between men and women within the autism group. The women with autism showed higher levels of autistic traits and social anxiety than the men, and it was primarily this group of women who exhibited the distinct pattern of looking away from the face. This suggests that the experience of social interaction and the way attention is allocated may vary considerably between genders within the autism community.

Ultimately, this research provides a sobering but necessary update to our understanding of social chemicals. It demonstrates that while the brain's opioid and oxytocin systems are active during social interaction, simply blocking or boosting them with a single dose does not automatically alter how a person with autism looks at another person. The study did not find evidence that these drugs could be used as a quick fix to improve eye contact in a natural conversation. Instead, the findings point toward a more complex reality where social attention is influenced by a mix of individual traits, gender, and the specific context of the interaction. The researchers conclude that future studies will need to look more closely at individual differences and perhaps try different doses or methods to understand how these chemical systems truly shape the way we connect with one another.