Anyone with a passing knowledge of biology knows that testosterone is the male growth hormone. It kicks in during puberty and is what makes blokes taller, stronger, hairier and generally moodier than they otherwise would be without it.

In men, testosterone levels generally remain fairly high until around the age of 30 when they start to lower (women also have testosterone, but in smaller amounts). It is responsible for fertility, bone density, sex drive, muscle strength and development, fat storage, and the production of red blood cells.

But testosterone’s applications don’t stop there. In the word of men’s fitness, testosterone boosters in the form of tablets, supplements or injections, can help signal our bodies to build muscle mass. Which sounds ideal if you’re tired of wolfing down turkey steak and chicken breasts in an attempt to add some size to your frame.

“Testosterone is associated with increased energy, fat loss, muscle gain, and improved mental function,” says nutritionist and functional medicine practitioner Steve Grant. “And who doesn’t want more energy, better body composition, increased strength and recovery and better cognitive performance?”

So if testosterone is such a wonder-drug, it makes sense that the more we can get in our systems, the better. Not so. While there have been countless scientific studies proving the benefits of testosterone, many of the wider effects are still up for debate. What’s more, the testosterone market is absolutely brimming with misinformation, from self-accredited experts documenting their bulking journeys on YouTube to websites selling an alarmingly broad range of unapproved products.

Scientific studies have for the most part been inconclusive on certain key questions around testosterone supplements. For instance, does upping testosterone provide you with this plethora of health benefits, or does being healthy simply promote increased levels of testosterone? A study published in the medical journal JAMA Psychiatry, for example, noted that men with depression also have low testosterone levels, but could not definitively say whether low testosterone levels cause depression, or depression causes low testosterone levels.