Studies exploring the neurochemical underpinnings of basic, evolutionary rewards (i.e. tasty food and sex) have consistently implicated the endogenous opioid system during peak moments of consummatory pleasure. Less is known about the role of opioids while listening to pleasant music, despite being rated one of the top 10 most rewarding human experiences. In fact, music is known to be so deeply and powerfully pleasant that it can elicit intense, emotionally-charged physiological sensations, or ‘chills’. We hypothesised that an opioid antagonist would decrease hedonic valence and/or arousal to self-selected, favourite musical pieces. Fifty male and female individuals participated in a music-listening task with a counterbalanced, placebo-controlled double-blind design. Participants were orally administered an opioid antagonist (50mg naltrexone) or placebo (40g d3-vitamin) over two sessions, a week apart. One hour after pharmacological intervention, participants listened to music while eye-tracking data was collected. The songs presented were self-selected pieces, highly pleasant and even chill-inducing for each individual participant. In addition, each individual listened to another set of (control) songs that were similarly provided by an age- and sex-matched individual. While listening to each musical selection, a participant looked at an on-screen visual analog scale termed the ‘chillometer’, directing gaze vertically along the ‘thermometer’ scale according to the felt moment-to-moment hedonic response. In the present study, music chills were found to last approximately four seconds with great inter-individual differences, a novel addition to the scientific literature on the duration of peak musical rewards. Results revealed that while hedonic valence was not systematically altered by naltrexone, there was a general diminished level of arousal to both song types, indexed by a smaller pupillary diameter and more so for ‘chilling’ moments, beyond the expected generic reductive effect naltrexone has on the pupil. Crucially, with naltrexone, pupil size during self-selected songs was smallest while experiencing music chills than for the other hedonic levels. These findings, taken together, suggest that the opioid system may modulate arousal more than hedonic valence, at least in relation to musical peak experiences as chills. Overall, our findings are only partially consistent with our initial hypothesis.