Military Testosterone Policy Raises Questions About Aggression

The U.S. military has a new plan to check the hormone levels of every service member over the age of 30. Defense Secretary Pete Hegseth announced the policy in July, saying he wants to build a 'High-T Department of War.' The idea is to test soldiers for low testosterone and offer treatment to those who qualify. But many doctors and scientists are asking whether the plan could cause more harm than good.

Testosterone is a hormone that the body makes naturally. It helps control energy, muscle growth, and mood. As men get older, their testosterone levels often drop. A treatment called testosterone replacement therapy, or T.R.T., can bring those levels back up. The military wants to use T.R.T. to keep troops strong and sharp on the battlefield.

Some men who have used T.R.T. say it helped them feel much better. Van O'Neill started taking testosterone 20 years ago after tests showed his levels were low. He said the treatment gave him more energy right away. But he also noticed a serious downside — he became much easier to anger. 'I felt like I had a coiled spring in my body that was wound real tight,' said O'Neill, who is now 67.

O'Neill remembered one moment at a support group meeting when another member jokingly touched his head. He jumped up and shouted, 'Don't ever put your hands on me!' He was shocked at how close he came to hitting the man. Since then, he has gone on and off the medication. He said, 'You've got to be careful with this stuff.'

Scientists have studied whether testosterone causes aggression, but the answer is not simple. Most studies show that T.R.T. does not make the average man more aggressive. However, researchers have found that the hormone can increase aggression in men who are already prone to angry or impulsive behavior. Those men seem to have a lower limit for what sets them off when they are on the treatment.

Robert Sapolsky, a scientist at Stanford University, explained it this way: 'People who are already aggressive are likely to become more aggressive.' He also pointed out that this could be a problem in the military. A soldier might not fight harder in battle, but he might be more likely to get into a fight with someone in his own unit.

Researcher Justin Carré ran studies where men were given either a single dose of testosterone or a fake pill, called a placebo. Then the men played a computer game where they could either score points or attack a fake opponent. When the opponent stole a point, men who already had dominant or impulsive personalities and had been given testosterone were more likely to focus on attacking instead of scoring. Carré said, 'Testosterone makes aggression more rewarding, whether or not it's productive.'

Some doctors worry about how the military will watch for these behavioral changes if thousands of troops start T.R.T. at once. Dr. Tom Hildebrandt, a psychiatrist in New York, said it is important to understand what the hormone does to decision-making. 'If I were a general... I would want to know: How does that affect their decision making?' he said. So far, the Department of Defense has not commented on the possible effects on troop behavior.

T.R.T. also carries physical risks. The hormone can cause the blood to thicken, which is dangerous and must be watched closely. It also stops the body from making sperm, which could affect a soldier's ability to have children in the future. Medical groups do not recommend testing everyone for low testosterone, because doctors fear it could lead to unnecessary treatment and bad outcomes.

The use of testosterone therapy has grown fast across the United States. In 2000, there were fewer than one million T.R.T. prescriptions. By 2025, that number had grown to nearly 12 million. Much of this growth has been driven by online clinics and social media influencers who promote testosterone as a way to feel stronger and more confident.

Not everyone who uses T.R.T. has problems with anger. A doctor named Richard said the treatment changed his life after cancer stopped his body from making testosterone. But his wife noticed he was snapping at her more often after he started the treatment. He worked with his doctor over many years to adjust his dose and manage his mood. He warned that the military might struggle to do the same careful monitoring for thousands of troops: 'Subtle effects, on that kind of scale, can be really serious.'