This study seems to show that minocycline helps to resist placing too much trust in attractive women.

Recently, minocycline, a tetracycline antibiotic, has been reported to improve symptoms of psychiatric disorders and to facilitate sober decision-making in healthy human subjects. Here we show that minocycline also reduces the risk of the 'honey trap' during an economic exchange. Males tend to cooperate with physically attractive females without careful evaluation of their trustworthiness, resulting in betrayal by the female. In this experiment, healthy male participants made risky choices (whether or not to trust female partners, identified only by photograph, who had decided in advance to exploit the male participants). The results show that trusting behaviour in male participants significantly increased in relation to the perceived attractiveness of the female partner, but that attractiveness did not impact trusting behaviour in the minocycline group. Animal studies have shown that minocycline inhibits microglial activities. Therefore, this minocycline effect may shed new light on the unknown roles microglia play in human mental activities.


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TL;DR of the paper:

98 human, male, japanese, Kyushu U students aged 20-30 took either (double-blind random assignment) minocycline pills or lactose pills for four days.

Then, during/after the interview on effects/side-effects of the pills, the interviewer "gave" them 1300 JPY and showed them a picture of a young female (of otherwise identical demographic). The male subject decided how much of the 1300 yen to "bet" by giving her, after rating how attractive she seemed and rating how trustworthy she seemed, and then if she cooperated they received 150% of this amount + 650 JPY¹, or nothing if she defected (and the woman kept what they gave her multiplied by three).² This exercise was repeated seven times, so one Game for each of the 8 pictures for each male participant.

Overall, mitocycline subjects seem to have given less money in general (at the mean), and lactose subjects seem to have given much larger fractions of 1300 JPY at the mean when they rated females more attractive - meaning that the effect is not only explained by a larger amount of males giving all the money, and may indicate that less males kept all the money.

The raw data is not available as far as I've found, so there's not much to go on to verify the statistical analysis.

1: Basic math should render it obvious that if the man gives less than 217 JPY, the woman will almost certainly defect, since cooperating otherwise would leave her with less money than she started with. See point 2 below for the logic of how the game worked.

2: As the game was explained to the male participants: Each of the two players start with 1300 yen, and the man chooses how much (or nothing) to give to the woman - this amount he gives is tripled, and then the woman decides whether to keep the new total (3 the gift + 1300) or split it 50-50 (and keep 1.5 the gift + 650). It is not specified, but I believe the men were led to believe that the woman would take her decision after learning how much they (the man) decided to share with her.


I wish we'd stop using lactose as a placebo.

Title could be a little more precise: Antibiotic seemingly improves men's decision-making in the presence of attractive women. The study does not speak to the drug's efficacy on women. As it stands, the title could be misread as saying that only men make decisions. (The study also apparently did not filter for the sexual orientation of the male subjects. And, likely on account of the researchers' location on Kyūshū, the subjects were all ethnically Japanese.)

As it stands, the title could be misread as saying that only men make decisions.

Not reasonably (ie. Such a reading would be fallacious). The actual potential misleading implication in the title is that it is a finding that both males and females have their decision-making improved in the presence of (other) women. I agree that it would be improved by changing it to, for example, "Antibiotic seemingly improves decision-making by males in the presence of attractive women."



We are in agreement here.


I don't know the mechanism of action, but it seems unlikely that this is acting as an antibiotic to have this effect.

More likely that minocycline is acting directly as a stimulant-blocker, dopamine-blocker or oxytocin-blocker.

Next experiment: examine the effect of stepped doses of modafinil and nasal administered oxytocin to see if they might 'rescue' the sweetness of the honey trap.

Agreed. , an incredibly potent dopamine reuptake inhibitor, was discovered while investigating antibiotics.

Also, reading here, I get the sense that this isn't the first time minocycline has been used to aid sober decision making.

Scientists think the drug may clear the brain of distractions like, in this case, arousal, to improve focus for making rational decisions. And these scientists aren’t the first to show that the antibiotic has effects other than getting rid of zits. Other studies have demonstrated that minocycline can improve patients’ focus on social cues, encourage sober decision making and improve the symptoms associated with schizophrenia and depression.

I'm interested in what other effects taking minocycline has. Often the same biological systems regulate or affect diverse phenomena. Case in point, I believe sickle cell trait offers resistance against Malaria, but also (under other circumstances) causes sickle cell anemia.

Does taking minocycline only improve rational decision making? If it does, does that increase fitness? I see three options which are worthy of some reflection.

  • Our trust mechanism are not optimal, minocycline improves our decision making and increases fitness.
  • Our existing trust mechanism offers good fitness. Perhaps trusting attractive females tends to pay off genetically, on average, and minocycline actually reduces genetic fitness (and perhaps increases things we consider more worthy).
  • There's some other third factor, yet unidentified, which increased rational decision making trades off against.

Anyone care to weigh in on this?

I'm wondering if it's harder for attractive women to trust men.

I also wonder if minocycline has the same effect on women taking it. I know that there are a few case studies in which minocycline has been tested on patients with Alzheimer's Disease to see if the drug improves cognitive function. I'm fairly certain it was tested on both men and women. I'll see if I can track down a few links.

Tetracycline antibiotics are known to cause Intracranial hypertension as a side effect. I wonder if there could possibly be a graded response where blood pressure is being increased, thereby improving blood flow to certain areas of the brain?