Do fertility supplements work?

The idea behind them is sound

Oxidative stress is a genuine and well-established contributor to male infertility. When the production of reactive oxygen species outruns the body's antioxidant defences, sperm motility, membrane integrity, mitochondrial function and DNA integrity all deteriorate.¹²³

But there is a catch built into the biology, and it matters later on this page: sperm need some reactive oxygen species to work. Capacitation and normal sperm function depend on them.¹⁴ This is a balance, not a substance to be eliminated.

What the trials actually show

Consistent improvement in the numbers. Much less in the outcomes.

The largest meta-analysis covered 45 randomised trials and 4,332 infertile men. It found significantly higher sperm concentration, progressive motility, total motility and normal morphology with antioxidants — and higher pregnancy rates. But of the four studies that reported live birth, none demonstrated an effect.⁵

That distinction runs through the whole literature. Semen parameters are easy to measure, quick to change, and are what most trials report. Babies are the outcome couples came for, and are what most trials do not report.⁶⁷

The two trials that ought to be better known

MOXI was a placebo-controlled trial of exactly the sort of combination sold in pharmacies: vitamin C 500 mg, vitamin E 400 mg, selenium 0.2 mg, L-carnitine 1,000 mg, zinc 20 mg, folic acid 1,000 µg and lycopene 10 mg, taken daily for three to six months.

It improved nothing. Not semen parameters, not DNA fragmentation, not pregnancy, not live birth.⁸

SUMMER, published in 2025, tested Impryl — a product widely bought in the UK — taken daily for six months in men seeking fertility care. It did not improve ongoing pregnancy or any secondary semen outcome. More awkwardly, pregnancy rates were lower during the four-to-six-month window in which the treatment was supposed to be working best.⁹

Two well-conducted placebo-controlled trials of the multi-ingredient formulas people actually buy, and neither showed a benefit worth having.

So is there anything with a real signal?

Yes, and it is worth knowing which, because the market treats all of these as interchangeable.

Carnitines have the clearest evidence for semen quality. A network meta-analysis of 23 randomised trials ranked L-carnitine first for motility, with a gain of 6.52%, and first for morphology, with a gain of 4.96% against placebo.¹⁰ A separate network meta-analysis in men with idiopathic oligoasthenoteratozoospermia reached the same conclusion, ranking L-carnitine — particularly combined with acetyl-L-carnitine — highest for concentration, progressive motility and morphology.¹¹

CoQ10 is the best-supported single agent. A 2025 meta-analysis of 8 trials and 877 men found improvements in total sperm count, total and progressive motility, normal morphology, testosterone and inhibin B — but no significant improvement in semen volume or sperm concentration, and substantial variation between studies.¹² Compared head-to-head with selenium in idiopathic cases, both improved concentration and motility, with CoQ10 producing larger gains in antioxidant status.¹³

Vitamins C and E have supportive data, including better pregnancy rates with vitamin E across 11 studies and 832 patients.¹⁴ Selenium with vitamin E improves motility, morphology and vitality, though pregnancy data remain thin.¹⁵

N-acetylcysteine and alpha-lipoic acid sit in the second tier. NAC at 600 mg daily for three months improved count and motility while reducing abnormal forms, DNA fragmentation and oxidative damage.¹⁶ Alpha-lipoic acid improved motility and morphology across five randomised trials but did not significantly improve pregnancy.¹⁷

Why the results contradict each other

Three reasons, and understanding them tells you what to do.

"Antioxidants" is not one intervention. Ingredient, dose, duration, patient selection and endpoint vary enormously between trials, which makes pooling them unreliable.¹¹⁸

Almost nobody selects patients by whether they actually have oxidative stress. Most trials recruit infertile men and give them antioxidants regardless of redox status.⁶¹⁹ Yet men with elevated oxidation-reduction potential or DNA fragmentation appear more likely to improve, while men whose antioxidant levels were already normal gain little.²⁰²¹ The MOXI investigators found precisely this when they looked at plasma antioxidant levels against semen parameters.²²

Varicocele shows the same subgroup dependence. Some meta-analyses report modest gains in men with untreated varicocele;²³ another found no clear improvement in pregnancy or semen parameters in varicocele-associated infertility where oxidative stress had not been screened for first.²⁴

The pattern is consistent: give antioxidants to everyone and the average effect is small. Give them to men who demonstrably need them and the picture may be different — but that trial has largely not been done.

The risks nobody prints on the box

Side effects are real, if minor. A meta-analysis of 13 randomised trials found more nausea, headache and dyspepsia with antioxidants than placebo, although not enough to make men stop taking them.²⁵ Cochrane found the same for mild gastrointestinal upset.²⁶

More is not better, and may be worse. Push the balance too far and you get reductive stress — too few reactive oxygen species, disrupting the maturation and capacitation that sperm require.²⁷²⁸

And this is not theoretical. A scoping review examined 34 over-the-counter male fertility products. It found that 79% exceeded the recommended daily allowance for at least one ingredient, and some exceeded the tolerable upper limit.²⁷

Four in five products on the shelf are dosed above the recommended intake for something. That is the part I would want a man to know before he starts stacking two of them.

Bottom line

Antioxidants are promising and unproven. They reliably move the numbers on a semen report — most convincingly the carnitines and CoQ10 — and they have not been shown to reliably produce pregnancies or live births, including in two good placebo-controlled trials of the exact formulas people buy.

Food-first remains the better-evidenced route. Dietary patterns rich in fruit, vegetables, fish and whole grains are associated with better semen quality, while smoking, heavy alcohol, excess weight, heat and pollution all push oxidative damage the other way.²⁹³⁰

I am not against supplements and I will not tell you to throw them away. I will tell you what the evidence actually supports, which is much less than the packaging implies, and I would rather you spent the money on a proper assessment first. If a varicocele or a hormone problem is driving this, no antioxidant will touch it.