The endorsement of conspiracy theories may be increased by subjectively perceived stress. Yet, it is not known whether this correlation is caused by the effects of the acute stress reaction on the brain or other psychological, social, or methodological factors. The effect of an experimentally induced acute stress reaction on conspiracy thinking was tested on a sample (n = 115) of students of medicine. Although the stress procedure caused a substantial increase in salivary cortisol, there was no significant effect on endorsing conspiracy theories or adopting conspiracy interpretations of novel information. The results confirmed no effect of the acute stress reaction on conspiracy thinking, suggesting it may be absent or weaker than expected. The study demonstrated the viability of psychophysiological experimental design in conspiracy research and may inspire further examination of the physiological mechanisms underlying susceptibility to conspiracy theories.