NAC Benefits for Men: Fertility, Sperm and What Is Unproven

The strongest male-specific NAC research is about fertility and semen quality. Human trials have examined sperm motility, semen volume, concentration, morphology and oxidative/antioxidant balance. Evidence for testosterone, muscle growth or “male vitality” is far weaker.

NAC benefits for men at a glance

Claim	Evidence
Semen quality	Promising randomized and pooled evidence.
Sperm motility	Consistent positive signal.
Pregnancy/live birth	Not established from semen data alone.
Testosterone	No strong evidence of a meaningful boost in healthy men.
Muscle growth/bodybuilding	Not established.

The 120-man randomized trial

A key randomized placebo-controlled trial enrolled 120 men with idiopathic infertility.

Participants received NAC 600 mg/day or placebo for three months. NAC improved semen volume, motility, viscosity and antioxidant status. Sperm count and morphology did not significantly differ in that individual trial.

This is meaningful evidence for semen physiology, but semen measures are surrogate outcomes. The trial did not prove a higher live-birth rate.

What does the 2025 meta-analysis show?

A 2025 meta-analysis of randomized trials assessed NAC and L-carnitine monotherapy for idiopathic male infertility.

Only three NAC-versus-placebo trials contributed to the NAC comparison, but pooled results favored NAC for several semen parameters, including ejaculate volume, concentration, motility and morphology.

The small number of NAC trials means the pooled estimates should not be treated as definitive fertility outcomes.

Why NAC might affect sperm

Sperm cells are vulnerable to oxidative damage because their membranes contain large amounts of polyunsaturated fatty acids and because oxidative stress can impair motility and DNA integrity.

NAC can support glutathione-related antioxidant systems and redox balance. That mechanism fits the semen findings, but it does not prove benefit in men whose infertility is driven by genetic, obstructive, endocrine or other causes.

Does NAC increase testosterone?

There is no strong human evidence establishing NAC as a reliable testosterone booster in healthy men.

Infertility studies sometimes measure reproductive hormones, but improvements in oxidative stress or semen parameters should not be repackaged as evidence that NAC meaningfully raises testosterone.

Can NAC improve pregnancy rates?

Possibly in some contexts, but the evidence is much thinner than the semen literature.

Improving motility or concentration can be biologically relevant, yet pregnancy and live birth depend on both partners and many additional factors. A supplement should not be credited with fertility success solely because a semen-analysis number improved.

How long were fertility studies?

The key randomized trial lasted three months, which roughly corresponds to the timescale over which spermatogenesis and maturation can be meaningfully reassessed.

That does not mean three months is a guaranteed time to conception or that longer use necessarily produces better outcomes.

What about bodybuilding?

NAC has exercise and fatigue research, but it is not a muscle-building nutrient comparable to protein or creatine. In some contexts, antioxidant interventions may even interact with normal exercise signaling.

We keep that evidence under NAC for exercise performance rather than using male fertility data to support gym claims.

Bottom line

For men, NAC's most credible specific benefit signal is semen quality in idiopathic infertility. The evidence is promising but still based on a relatively small clinical literature, and semen improvements are not the same as proven live-birth benefit. Testosterone and bodybuilding claims are much less supported.