Researchers took the top 16 testosterone and 16 erection supplements at the most popular US online retailers, pulled out their 37 ingredients and found 105 trials — but “no whole supplement products have published RCT evidence.” And reports of better libido fell 91% once untrustworthy reviews were filtered out.
Of 3,334 men, 277 had a normal total testosterone but a low free one, and more sexual and physical symptoms on average; 96 had the reverse and mostly did not. A smaller study disagrees. Plus the three ways a lab gets a free number, and the one the guideline says not to use.
In men with obesity, losing weight by diet raised total testosterone about 72 ng/dL on average across 19 studies, and bariatric surgery about 208 across 26. Vitamin D did nothing in the trials. The famous sleep-deprivation figure rests on ten men and a p-value of .049.
In healthy men aged 19 to 39 the harmonised normal range is 264 to 916 ng/dL: the man at the top has three and a half times the man at the bottom. One reading under 300 is not a diagnosis; the guidelines ask for two early-morning tests and symptoms. And in 197,883 men, time of day moved the number more than decade of life did.
The US military now screens every service member over 30. The Endocrine Society’s guideline recommends against routine screening of men in the general population, at its strongest grade. And a glucose drink pushed 15% of men with normal testosterone into the hypogonadal range.
Cortisol falls in the pooled trials, most of them paid for or supplied by the extract makers. Whether people feel less stressed is contested. Sleep is the best-supported claim, testosterone rises in men but not women, and liver injury is very rare but can be severe.
Pooled across 15 randomised trials of berberine and barberry, people lost 1.9 lb more than a comparison group. Semaglutide, in the trial that made it famous, beat placebo by 28 lb. Both are measured the same way, from the best evidence available for each.
The trial behind the 2024 headlines was retracted in September 2025, four days after a meta-analysis pooled it, and a year on that meta-analysis still carries no correction. What survives: a real but modest effect on blood sugar after meals, and about 2 lb of weight across twelve short trials, most of it back within a month of stopping in the one trial that checked.
Partially hydrogenated vegetable oil genuinely harmed people: when 11 New York counties restricted trans fat in eateries, hospital admissions for heart attacks and strokes fell an extra 6.2%. The FDA has since banned it. The fear outlived it and reattached to the oil that's left, which is usually soybean, as the ingredient list will tell you.
Eggs raise LDL by about 5 to 8 mg/dL in the pooled trials, so "eggs don't affect your cholesterol" is wrong. Whether that matters for the heart is disputed: in six US cohorts the egg's link with heart disease followed the cholesterol in its yolk, and the big pooled analyses disagree. And two meta-analyses disagree about the one thing the "it's a wash" argument needs.