More men are getting testosterone treatment – but there’s a catch

This is Everyday Science with Clare Wilson, a subscriber-only newsletter from The i Paper. If you’d like to get this direct to your inbox every week, you can sign up here. Hello, and welcome back to Everyday Science. From now on, all US military personnel aged 30 and over will have testosterone testing as part of their yearly health check, Defence Secretary Pete Hegseth has said. If levels are too low, they will be offered voluntary injections of the male sex hormone. Hegseth says this is necessary so troops can operate at their “absolute best”. But he isn’t the only one concerned about men’s hormone levels. Testosterone use has been rising both in the form of illegal online purchases by some gym goers and legitimate prescriptions to men worried about “low T”. Shorts But testosterone treatment has downsides as well as benefits. Testosterone has multiple functions in the body. In men, it is made in the testicles and is necessary for sperm production as well as having a role in the sex drive. It also helps support muscle and bone tissue and influences mood and energy levels. Farmers have long known that the testicles produced some substance important for virility, as they would remove them to produce more docile animals. In the early 20th Century, some doctors even offered men implants of monkey gonads as a cure for ageing. While there are no records of the success or otherwise of this supposed treatment, there was a grain of truth behind it. Men’s testosterone levels do naturally decline with age, by about 1 per cent a year. And if levels fall faster than average, then it can lead to symptoms such as erectile dysfunction and low libido, as well as fatigue and depression. “If you’re losing it at 5 per cent per year, then the symptoms come on much more severely,” said Dr Geoff Hackett, a urologist and former professor of men’s health at the University of Bedfordshire. How testosterone therapy works Modern testosterone replacement therapy (or TRT) no longer relies on monkey glands, thankfully; instead, the artificially made hormone is given by regular injections or a gel that is rubbed into the skin. The average level for a man in his twenties or thirties is about 17 nanomoles per litre of blood. If it falls below 12 nmol/L, when tested on two occasions, then men are eligible to start TRT through the NHS. And more and more men are taking that opportunity. The number of testosterone prescriptions dispensed in England rose by 50 per cent between 2020 and 2024, according to figures from the NHS Business Services Authority. Some men access it through private online doctors if they are too embarrassed to see their regular GP, said Hackett. “Men are harder to get to the GP in the first place,” he said. “And they aren’t good at standing up for themselves.” As with all medical treatments, there can be side effects from TRT, like hastening the onset of male pattern baldness and it can also affect mood. These effects are more likely in those taking steroids who may be using higher doses for body building or to improve their physical performance. Some studies have described the phenomenon as “roid rage”. For a long time, there were also concerns that testosterone raised the risk of heart attacks and prostate cancer. But a landmark trial in 2023 in over 5,000 men showed that does not happen. There was, however, a slightly higher rate of blood clots in the lungs in the men taking TRT, but the rate was still very small, at 0.9 per cent compared with 0.5 per cent in those on placebo treatment, after three years. Infertility risk If that trial put to bed safety fears, then perhaps Hegseth’s new testosterone screening plans have no downside? Not so fast, said Professor Allan Pacey, an andrologist at the University of Manchester. Testosterone therapy has a further side effect that may be of less interest to older men who traditionally were the main users, but may be seen increasingly as use rises. It reduces sperm count. That’s because of a feedback loop, seen with many different hormone systems in the body. Normally, cells in the testicles make testosterone, which encourages production of two further hormones in the brain’s pituitary gland that are needed for sperm production. If you add testosterone to the blood, that fools the pituitary gland into “thinking” the testicles are making more testosterone than they really are and so it reduces levels of those two pituitary gland hormones, thereby shutting down sperm production. The effect can happen with people taking prescribed TRT at the correct dose, but is even more likely with those using illicit testosterone, which could be sourced online, who may not be aware of the potential for this side effect. “The classic presentation is a bodybuilder walks into a fertility clinic, they’ve been trying for a baby with their partner for a few years, and it’s not been working,” said Pacey. “You do a sperm test, he discovers he’s got no sperm. You explain it, and then [his partner] is really mad with him.” Sperm levels do recover but it can take up to a year. Mass screening not necessary Pacey does not believe mass screening is necessary, because TRT should really only be offered to men with demonstrable symptoms as well as proven low testosterone levels. “Most men who’ve got a serious testosterone deficiency would probably be going to their GP with symptoms,” he said. Three Australian public health doctors have argued that the US focus on testosterone levels is a sign that the Trump administration has embraced “manosphere” beliefs that men’s virility is under threat from modern life. “The policy presents testosterone levels as a measure of ‘manhood’,” they have written on the academic website, The Conversation. “Testosterone therapy can lead to physiological dependence. This makes it difficult to stop treatment without symptoms such as fatigue, reduced libido and erectile dysfunction.”