NAC
Find NAC, short for N-acetylcysteine, in capsules and powder. We explain how it relates to the amino acid cysteine, which form suits daily use, why it smells of sulphur and what the label may and may not say.Read more →
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What N-acetylcysteine is and how to choose your NAC
NAC is short for N-acetylcysteine. It is a stable form of the amino acid L-cysteine, which your body also gets from protein-rich food such as eggs, cheese, chicken and yoghurt. The acetyl group is a small chemical addition that keeps cysteine stable in a capsule, which is why supplements use this form rather than plain L-cysteine. That also makes NAC one of the more distinctive products in our range of amino acids.
In the UK you will also come across acetylcysteine as a prescribed medicine. Food supplements are a separate category with separate rules. That has one honest consequence for this page: the European food safety authority (EFSA) has not authorised a health claim for cysteine. So we do not promise you an outcome. What we can be precise about is the form, the amount per serving and how to use it sensibly.
Forms and strengths in this collection
Nearly everything here is free-form N-acetyl-L-cysteine, which means it is already in a single usable form and needs no breaking down first. The real differences are practical:
- Capsules: a fixed amount per serving, and the shell keeps most of the sulphur smell inside.
- Powder: you set your own amount and can split it across the day, but the taste is sharp and sulphurous.
- Complexes: NAC alongside ingredients that act on the same pathway, such as selenium, vitamin C or alpha-lipoic acid.
Strengths on the UK market usually run from 300 mg to 600 mg per capsule. Most brands settle on 600 mg. A 300 mg capsule is useful if you want to start lower or spread your intake over two moments in the day.
How we choose the NAC we stock
Three things decide whether a NAC product appears on this page: the form, the amount per serving and whether any added ingredients earn their place. We prefer free-form N-acetyl-L-cysteine with the strength stated clearly on the front, so you know exactly what you take. Complexes only make the cut when the extra ingredients act on the same pathway, not when they pad out a label. We buy directly from the brands, our compliance team checks every product before it goes live, and independent labs spot-check batches. You can read how we select brands and products.
Who it suits and what to expect
NAC suits adults who eat little protein-rich food, including some vegetarians and vegans, and anyone who wants cysteine in a fixed daily amount instead of guessing from diet. It sits close to our other antioxidant supplements in the way people use it, as a steady daily habit rather than a short course.
Be practical about the details. UK labels state that NAC is not for children and not for use during pregnancy or breastfeeding. Take it with a meal if your stomach is sensitive. Speak to your GP first if you take any medication, including blood thinners, or if you have asthma or a stomach ulcer. The eggy sulphur smell when you open the pot is normal for this amino acid, not a sign of a bad batch. And give it two to three weeks of consistent daily use before you judge it: NAC is a slow, steady supplement, and that is exactly how it is meant to be used.
Frequently asked questions
NAC stands for N-acetylcysteine, a stable form of the amino acid L-cysteine. Cysteine is one of the amino acids the body uses to build proteins, and it is one of the few that contains sulphur. Supplements use the acetylated form because plain L-cysteine is less stable in a capsule or pot. On labels you will see it written as N-acetyl-L-cysteine, N-acetyl cysteine or simply NAC. All three refer to the same ingredient.
