A new study has found that administering testosterone to weakly affiliated Democratic men reduced their identification with the Democratic Party and made them feel significantly warmer toward Republican presidential candidates. The hormone had no similar effect on strongly affiliated Democrats or Republicans. These findings suggest that short-term changes in biology can influence political preferences—at least for those who are less firmly attached to their political identity.
The research was published in the journal Brain and Behavior and adds to a growing body of work examining how neuroactive hormones shape human behavior in subtle but measurable ways. In this case, the hormone under investigation was testosterone, which is best known for its role in shaping male traits such as muscle growth and sexual function but also influences behavior through its action in the brain.
The scientists behind the new study had previously found the hormone oxytocin boosted interpersonal trust overall and led Democrats with initially low trust levels to express greater trust in both Democratic and Republican politicians, as well as in the federal government.
They were interested in testosterone because of its wide-ranging effects on decision-making, competition, and social behaviors. Higher testosterone levels have been associated with traits such as risk-taking, dominance, and reduced empathy, all of which may influence how people evaluate political messages and candidates. Past studies have shown that men with higher testosterone tend to be more competitive and less supportive of redistributive policies, which are typically associated with liberal platforms.
“My current work is examining how small factors change decision-making,” said study author Paul J. Zak, a professor at Claremont Graduate University, director of the Center for Neuroeconomics Studies, and author of The Little Book of Happiness. “We had shown in a 2013 publication that administration of the neurochemical oxytocin changed political preferences for weakly affiliated Democrats. Testosterone is the ‘anti-oxytocin’ in terms of its behavioral effects and to confirm our previous finding that weak Dems are more susceptible to influence, we ran the current study.”
To investigate, the research team recruited 136 healthy young men with no serious health conditions. The average age of participants was 22, and they were ethnically diverse. Before starting the experiment, the researchers collected blood samples to measure each participant’s natural testosterone levels. Participants were also asked about their political affiliation—whether they identified as Democrats, Republicans, or Independents—and how strongly they felt connected to their chosen party. On average, Democrats made up 44% of the sample, while Republicans were just over 8%, with the rest identifying as Independents or having no clear affiliation.
To test how testosterone might influence political preferences, participants were randomly assigned to receive either a single dose of synthetic testosterone gel or a placebo gel that looked and felt the same. The experiment was conducted in a double-blind fashion, meaning neither the participants nor the researchers knew who received testosterone and who received the placebo. The gel was applied to the participants’ shoulders and upper back, and they returned the next day for follow-up tests, including a second blood draw to measure testosterone levels after the treatment.
The researchers used surveys to assess political feelings. On the second day, participants rated their warmth or favorability toward a set of prominent Democratic and Republican presidential candidates using a “feeling thermometer” scale ranging from 0 to 100. Higher scores meant greater favorability. Participants also rated how strongly they identified with their political party and completed measures of mood and anger to rule out emotional side effects of testosterone.
Before any treatment was given, the researchers noticed that weakly affiliated Democrats—those who said they didn’t feel strongly tied to the Democratic Party—had higher natural testosterone levels than their strongly affiliated counterparts. In fact, weakly affiliated Democrats had about 19% higher basal testosterone on average than strong Democrats. This difference did not appear among Republicans.
When researchers looked at what happened after testosterone was administered, they found that the hormone significantly changed political attitudes—but only in one group. Among weakly affiliated Democrats who received testosterone, the average strength of their identification with the Democratic Party dropped by about 12%. These individuals also reported a striking 45% increase in warmth toward Republican presidential candidates.
“The size of the change in preferences was very large, indicating it was not a fluke,” Zak told PsyPost.
In contrast, strongly affiliated Democrats and all Republicans, whether they received testosterone or placebo, showed no meaningful changes in political affiliation or feelings toward the opposing party.
“As in our oxytocin administration study, testosterone had no effect on any Republicans or strong Democrats,” Zak said. “These appear to be true believers, even weakly affiliated Republicans.”
The researchers concluded that testosterone appears to make weakly affiliated Democrats more open to Republican candidates and less connected to their own party. This specific response did not seem to be driven by mood or emotional changes. Measures of positive affect and self-reported anger remained stable across all groups, suggesting that the shift in political attitude wasn’t due to increased aggression or happiness. It also wasn’t explained by general changes in emotional intensity.
This change in political views was not observed in Independents or Republicans. Among these groups, testosterone did not alter feelings toward either Democratic or Republican candidates, nor did it influence party identification. This suggests that the effects of testosterone are selective, emerging only in people with a particular combination of weak political identity and biological traits—specifically, higher natural testosterone levels.
The researchers believe these results reflect how hormone levels may amplify or unmask existing but latent preferences, especially in people who are undecided or only loosely aligned with a political party. One possible explanation is that testosterone interacts with brain regions involved in decision-making and risk, such as the striatum. In prior research, testosterone has been shown to increase dopamine activity in this region, which is involved in anticipating rewards and making bold choices. This might explain why testosterone shifted attitudes in a group already showing greater biological sensitivity.
Another possibility is that some weakly affiliated Democrats may feel social pressure to identify with a liberal party but hold more conservative views privately. The testosterone administration may have reduced that internal conflict, allowing them to express preferences that were already present but not consciously endorsed. Since testosterone has been linked to dominance and self-assertion, it may have given participants the psychological confidence to report attitudes that diverged from their stated affiliations.
“People’s stated preferences may not correspond to actual behaviors,” Zak explained. “We showed that people who self-identified as weak Democrats had basal testosterone higher than all other groups, suggesting they are ‘wolves in sheeps clothing’ or wanted to be ‘cool’ by stating their liberality even in an anonymous survey. We changed this self-report with testosterone. There is some evidence that men who are physically stronger, typically those with higher testosterone, are more likely to support conservative views and our testosterone treatment mimicked this effect.”
“Second, weakly affiliated Democrats appear to be the swing voters politicians covet and they, unlike the other political groups tested, are more effectively unconsciously influenced by neurochemical changes based on both of our published studies. If political operatives want to influence these swing voters, they should think about ads and live events that increase testosterone. Many of the Trump rallies, at least what I saw online, were very ‘muscular’ with America-first slogans. So, our controlled study provides some insight into why so many voters swung towards Trump.”
But, as with all research, the findings come with limitations. One major constraint is the sample itself. Most participants were young men, many of whom were college students. Republicans were underrepresented in the sample, which means the results may not generalize to the broader population. Testosterone was only administered to men because the gel used in the study is only approved for males. Future research will need to examine whether similar effects occur in women, or in older adults, or in more politically balanced samples. The study also measured only self-reported attitudes, not actual voting behavior or campaign support.
However, the results raise intriguing questions about how campaign messaging and social environments might influence swing voters by triggering biological changes like testosterone increases.
“We are not advocating drugging voters,” Zak said. “Testosterone is a controlled substance and was used here to determine the causal effect on political preferences. Yet, many competitive settings increase testosterone so our work does correspond, in a controlled way, to experiences outside the lab. For example, winning a sporting match, even chess, raises testosterone, as does watching ‘your team’ win a game on TV.”
Looking ahead, the research team hopes to explore how these effects play out in other populations, including women and older adults. They are also interested in linking hormonal changes to actual political behaviors, not just reported preferences. Their broader goal is to understand the ways in which unconscious biological processes shape decision-making. “My group continues to examine decision inconsistency and where this comes from in the brain so that people can make better decisions and live happier lives,” Zak said.
“The most general interpretation of our findings is that people are malleable in ways they themselves do not consciously understand,” he added. “So, we should be kind to everyone as we’re not aware of our unconscious emotional motivations for our preferences and behaviors. I say that ‘everyone is a weirdo’ and that makes life interesting!”
The study, “Testosterone Administration Induces a Red Shift in Democrats,” was authored by Rana Alogaily, Giti Zahedzadeh, Kenneth V. Pyle, Cameron J. Johnson, and Paul J. Zak.
