A 2003 meta-analysis examined 250 supplements; only six had enough studies to analyse and only two worked. Creatine was one. Modern trials put it at about 2.5 lb of extra lean mass in under-50s — and 3 lb in older adults.
Cochrane pooled 86 trials and 162,796 people: little or no difference to dying or to cardiovascular events, at high certainty. The 4-gram prescription trial that cut heart events used a disputed placebo, a 2025 trial found fewer heart events in people on dialysis, and the atrial fibrillation risk is clearest at prescription doses.
Two big trials and a meta-analysis agree that testosterone therapy lifts sex drive in men with confirmed low testosterone; its effects on energy and mood are small. The largest trial found no rise in heart attacks or strokes, but more heart-rhythm problems, lung clots and kidney injury, and the largest trial to count fractures found 43% more of them.
Twelve men trained both arms for 15 weeks, one arm recovering in a bath of exercise-induced testosterone and growth hormone. The arm with no hormone spike grew 12%. The hormone-bathed arm grew 10%. Two larger studies from the same lab found no link with testosterone either.
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.