More and more men tell me they're just on a low dose of testosterone. And they often make the mistake of calling it TRT (testosterone replacement therapy). If a man doesn't have low testosterone and the symptoms that come with it, there is nothing to replace.
Put another way: if your body produces testosterone and what you want is higher levels, we're not talking about replacement. We're talking about a cycle.
And before we go on, there's no moralising on this side. We're just going to call things what they are, with no illusions.
Your body produces somewhere between 3 and 10 mg of testosterone a day, depending on the person. In work by Vierhapper published in the Journal of Clinical Endocrinology & Metabolism in 1997, the average came out at 3.7 mg a day.
A replacement dose exists to substitute that production, not to go past it. In practice that's 75 to 100 mg a week of injectable testosterone, with a defined target: to put you in the middle of the normal range, around 400 to 700 ng/dL on your blood work. And it's only justified when two things are true at once: repeated morning blood tests with low values (the usual reference is below 300 ng/dL) and symptoms behind them, such as low libido, erectile dysfunction, constant fatigue, low mood, loss of muscle and strength. This is what the Endocrine Society, the international endocrinology society, sets out in its 2018 revision.
A man with 280 ng/dL and no complaints is not a candidate for replacement.
In former anabolic steroid users whose bodies stopped being able to produce, as is my case. In young men who show up at the clinic with severe hypogonadism. Past steroid use is now the most common cause, and recovery is a lottery: most men return to their own values 1 to 2 years after stopping, and there's a portion that never does. A Danish study published in PLOS One in 2016 followed up former users years after they had stopped and found them still with low testosterone and all the symptoms.
In men with problems in the testicles themselves: genetic conditions such as Klinefelter syndrome, damage from infections, trauma, chemotherapy. Or with problems in the pituitary, the gland that gives the order to produce.
And in older men who meet the same requirements. Testosterone declines with age, from the early thirties onwards, something like 1% a year in the reference study on this, the Baltimore Longitudinal Study of Aging, published by Harman in 2001. At 60 or 70, there are men genuinely below the threshold and with symptoms, and those men are candidates for replacement like anyone else. Notice the measure is the same, repeated low blood tests plus symptoms. Being 55 and feeling less energetic than at 25 is not, clinically, enough for replacement.
Men who start using drugs usually begin at 250 mg of testosterone a week. It sounds like little when you hear it, especially next to the doses of men who compete.
Do the maths with me. 250 mg a week is about 36 mg a day, and since part of the weight in the vial is the ester, what actually goes in as testosterone is around 26 mg a day. Your body makes 3.7. We're talking about seven times what you produce, and double what any replacement would ever give you.
There's nothing "low" about this. It's the starting dose of a cycle, and it's called low only next to the doses of men already halfway down that road.
Your body controls production with a warning system. The brain measures how much testosterone is circulating and sends orders to the testicles through two hormones, LH and FSH. When testosterone arrives from outside, the brain reads high levels and stops sending the order. With no order, the testicles stop their own production and also stop making sperm.
This isn't a risk that might happen. It's the guaranteed effect, and it's so reliable that testosterone has been trialled as a male contraceptive. The World Health Organization ran that trial in the 90s: 200 mg of testosterone a week left about three quarters of the men with no sperm at all after six months. Notice the dose, which is less than the 250 mg we talked about.
Two consequences follow that you can see. The testicles shrink, because they've been left with no work. And fertility disappears for as long as it lasts, with the average time to a zero count sitting around three and a half months.
In replacement done under medical supervision this happens too, which is why a man who still wants children has to discuss it with his doctor before starting. There are ways to protect sperm production during treatment, such as hCG, which mimics the order the brain stopped giving.
The difference between the two cases is the starting point. A man on replacement already wasn't producing, and the system was already off before he began. A man on a cycle was producing normally and switches off a system that was working, counting on switching it back on when he stops. Sometimes it comes back. Betting on that is how I ended up with no production of my own for the rest of my life.
Replacement, done properly in the men who need it, has been studied. The TRAVERSE trial, published in the New England Journal of Medicine in 2023, followed 5,246 men with hypogonadism and high cardiovascular risk, and testosterone produced no more heart attacks, no more strokes and no more deaths than placebo.
At cycle doses the picture is different.
Heart. In 2017 Baggish published work in Circulation with 140 experienced weightlifters, 86 of them users. The heart pumped worse in users, with an average ejection fraction of 52% against 63% in men who had never used, and 49% in those using at the time of the scan. They also had more plaque in their coronary arteries. The Dutch HAARLEM study showed that left ventricular function improves after stopping. The plaque in the coronaries does not go away.
Kidneys. In 2010 a team published ten cases in the Journal of the American Society of Nephrology of bodybuilders with years of use: severe protein loss in the urine and kidney failure, with biopsies showing focal segmental glomerulosclerosis, scarring in the kidney's filter. Most improved after stopping and losing weight, but not all.
Brain. Norwegian researcher Astrid Bjørnebekk studied the brains of 130 long-term users with MRI and found less brain volume and a thinner cortex than in weightlifters who had never used. In later work, she used models trained on almost 1,900 healthy men to estimate a brain's age from the images: the users' brains came out older than they were.
Sleep and clearing the brain. During sleep, the space between brain cells increases by around 60% and the brain uses the time to wash out the waste it accumulated during the day, including beta-amyloid, the same protein that builds up in Alzheimer's disease. It's called the glymphatic system and it was described in work by Xie published in Science in 2013. A 2019 review in Neuroscience and Biobehavioral Reviews raised the hypothesis that high dose use favours the build-up of these proteins and raises the risk of dementia years later. That is a hypothesis built on mechanisms, not a result proven in people. What is established is the other end: users sleep worse, and sleep is when this clearing happens.
Head and behaviour. Pope's trial, published in the Archives of General Psychiatry in 2000, gave 600 mg of testosterone a week or placebo to 56 men, with neither them nor the investigators knowing what they were getting. Most of the men didn't feel much. A small group became slightly wired: more irritable, sleeping less, mind racing. And a smaller group still had a strong reaction, with irritability, aggression measured in tests, and behaviour the investigators classified as hypomania, a state of excitement in which a person becomes elated, impulsive and short-fused. There's no way to know in advance which of these groups you'll fall into.
On length of use. The damage tracks the total accumulated over a lifetime, not the peak dose. In Baggish's work, coronary plaque rose with every ten years of accumulated use, and in more recent Danish data the changes were more marked in men with over five years of use. A low dose kept up for years is a long exposure, and in that there's nothing safer about it than a short cycle.
The rest of the list applies to both cases, with different severity depending on dose: the blood thickens and haematocrit rises, blood pressure rises, good cholesterol drops, acne appears, and some men develop breast tissue. In replacement this is watched with routine blood work and the dose is adjusted. In a cycle bought off the internet, nothing is watched.
There's an industry living off this confusion. Online clinics that ask you a few questions, order a few tests and send testosterone to your door with the label of treatment.
They've been studied. In 2023, in JAMA Internal Medicine, a team led by urologist Justin Dubin posed as a patient across seven American men's health platforms. The fictional patient had normal testosterone and said he wanted children soon. Six of the seven offered him testosterone anyway. About half of the providers didn't warn him it would wreck his fertility.
The business model explains the result. The consultation is cheap or free, and the money comes from selling the product. The people assessing you are the people selling to you.
A prescription doesn't turn a cycle into treatment. What defines replacement is the diagnosis behind it: repeated low blood tests, symptoms, and someone following you who doesn't earn more by selling you more.
Show me the blood work. Not from some afternoon, from two different mornings, fasted. And tell me what you're feeling.
The man who asks me this is usually in his early thirties with normal blood work. He sleeps five hours a night, hasn't followed a training plan in two years and eats badly.
That counts. One week of sleeping five hours a night is enough to lower testosterone in young healthy men, in work by Van Cauter published in JAMA in 2011. Sleep, food and training move the numbers.
If the blood work really is low and the symptoms are there, the way forward is a doctor. An endocrinologist or a urologist, not an online clinic that makes its living writing prescriptions.
And if the decision is to use drugs knowing what they are, without calling it treatment, that's an adult's decision and I'm not the one who's going to make it for anyone. I just want the difference to be understood. Replacing what's missing and adding to what's already there are not the same thing.
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