When it comes to supporting fertility, making strategic supplement choices can help. If you’ve explored fertility supplements before, you may have come across N-acetyl-cysteine (also known as NAC). But what is NAC? Is it just another supplement, or does it actually deserve a spot in your routine? Let’s break down the claims and what the science says about NAC for fertility. What is NAC? What does N-acetyl-cysteine do? Does NAC help with fertility? What to look for in a NAC supplement for fertility? When to take NAC What is NAC? NAC is the supplement form of L-cysteine, an amino acid your body uses as a building block. Your body needs L-cysteine to make glutathione, often called the “master antioxidant.” (Antioxidants protect your cells from free-radical damage—learn more about them here.) NAC boosts levels of glutathione and also acts as an antioxidant (but spoiler: it actually does so much more). The supplement has a long history of use in hospitals to thin mucus in lung conditions and to support liver health (fun fact, it’s teh standard antidote for acetaminophen overdose).. But researchers are increasingly looking at NAC benefits for fertility. What does N-acetyl-cysteine do? NAC, or N-acetyl cysteine, works mostly behind the scenes in three main ways: It makes glutathione. Glutathione neutralizes oxidative stress, the cellular “rust” that can damage both eggs and sperm. It may improve insulin sensitivity. A 2023 meta-analysis found NAC improved metabolic markers in women with PMOS (formerly PCOS), and many people tolerated it better than metformin. It may help calm inflammation. Research has linked NAC to lower markers of inflammation and oxidative stress, including homocysteine, which is tied to egg quality and pregnancy health. Shop Now Does NAC help with fertility? For females Most NAC fertility research in women focuses on PMOS. A large 2025 meta-analysis found that NAC was linked to higher progesterone and a thicker uterine lining. (Both matter for pregnancy and implantation.) An earlier meta-analysis also found it may lower testosterone levels, which can help restore ovulation. In women with PMOS seeking fertility care, clomiphene citrate (Clomid) is often offered as a first-line treatment, but upwards of 40% experience resistance to treatment. Research shows that when Clomid is taken alongside NAC, ovulation rates rise significantly. The same study also found an additional benefit: NAC thins cervical mucus (the same way it breaks down thick mucus in the lungs in cases of bronchitis), allowing sperm to swim more easily toward an egg. In those preparing for egg retrieval, NAC supplementation reduced the chances of ovarian hyperstimulation syndrome (OHSS, a debilitating side effect of fertility medications), and significantly boosted egg retrieval count and pregnancy rates. In addition to NAC improving pregnancy rates, research has also demonstrated its benefit for recurrent unexplained pregnancy loss when taken alongside Folic Acid. Pregnant women supplementing with NAC and Folic Acid up to and beyond 20 weeks gestation had higher live birth rates compared to Folic Acid supplementation alone. For males Sperm are especially vulnerable to oxidative stress because of their fatty composition and lack of free radical defence. As a result, sperm require higher levels of antioxidants to combat the effects. A recent meta-analysis found that men taking NAC had better semen volume, sperm concentration, total motility, and morphology. In another study, infertile men were given NAC for 3 months. Similarly, semen and sperm parameters statistically improved, and so did hormones driving fertility (LH, FSH, testosterone). The caveat: research is limited to measuring sperm count, quality, and shape rather than pregnancy or live birth rates. While the data is encouraging, we need more long-term studies in this area. See Product Debunking Folic Acid Misinformation Read More What to look for in a NAC supplement for fertility? When choosing a NAC supplement for fertility, look for the right form: “N-acetyl-L-cysteine” with the milligrams per serving clearly listed. And as with any supplement shopping, look for third-party tested formulas and, if you’re trying to conceive, products formulated by experts like OB/GYNs and naturopathic fertility-focused doctors. NAC also works well alongside nutrients like other antioxidants (Vitamin E, Vitamin C), CoQ10, and Folic Acid (to name a few). Depending on your situation, a formula that fits your whole routine may serve you better than a stand-alone bottle. When to take NAC NAC is considered a biologically active supplement (it works well with the body’s natural processes) and, as a result, has a high safety profile. Still, you should speak with your naturopathic or fertility doctor prior to supplementing—especially if you are already pregnant or taking other medication. For women and men who are planning for conception, it’s best to start taking NAC 3 months in advance: the time that it takes for eggs and sperm to mature and when they’re particularly susceptible to support. (Though it’s never too late to start if you’re trying to conceive now!) From improving antioxidant status and lowering inflammation to supporting women through ovarian stimulation and increasing live birth rates, NAC’s wide range of uses and benefits make it a supplement worth considering. Speak with your naturopathic or fertility doctor to discuss if it’s right for you! Dr. Samantha Van De Wal, ND Inspired by her own PCOS journey, Dr. Samantha Van De Wal is a naturopathic doctor and mom committed to empowering others in their fertility and reproductive health. 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