L-cysteine is an amino acid that contains sulfur. It can be formed in the body from methionine, which is also a sulfur-containing amino acid. Because cysteine can be easily oxidized into cystine, the stable form of L-cysteine, N-acetylcysteine (NAC), is preferred for nutritional supplements.

NAC is also the originator of glutathione, which is a combination of the three amino acids cysteine, glycine, and glutamic acid. A combination of three amino acids is referred to as a “tripeptide”.

Applications for L-cysteine

L-cysteine for hair growth

Cysteine and Hair GrowthCysteine is a fundamental ingredient in the synthesis of collagen. Collagen, in turn, is the most important element for the production of keratin in hair. Collagen is also required for supporting healthy skin and nails.

A study conducted with women suffering from diffuse hair loss found that taking cysteine in combination with millet seed extract and pantothenic acid can lead to a normalization in hair growth after just three months of therapy 1.

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Which are the most important nutrients for healthy hair?

L-cysteine, iron, silicon, L-arginine, zinc, biotin, pantothenic acid. These are the ones your hair needs to grow!
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Cysteine for cell integrity and quality of semen

Cysteine and sperm qualityCysteine is the direct precursor to glutathione. The tripeptide glutathione is one of the most powerful antioxidants and protects cells from oxidative stress.

General studies have been conducted to determine the effects of glutathione on the immune system and aging processes. More recently, additional studies have focused on glutathione’s effect on sperm development in men.

These studies have shown that taking glutathione can significantly improve sperm development 2. A study involving male students under exam stress showed that stress contributes to low glutathione levels in semen and low quality of sperm 3.

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How can I increase the likelihood of a pregnancy?

In addition to L-cysteine, other amino acids, vitamins, and antioxidants have clear positive effects on the chances of a pregnancy.
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In cases of cough, NAC is generally recommended at a dose of 600 mg per day as a medication to dissolve mucus. Please pay close attention to dosage recommendations of medications.

For long-term therapy, a dose of 50 mg – 100 mg L-cysteine is recommended. The amino acid is available in the form of a safe nutritional supplement.

Side Effects

In the form of N-acetylcysteine (NAC), cysteine stimulates production of secretions and thereby dissolves mucus. To relieve coughing, it is primarily used as an expectorant. When using an expectorant, be sure not to take a cough suppressant.

L-cysteine is well tolerated when taken in the long-term dosages indicated above.


  1. Gehring W, Gloor M. Das Phototrichogramm als Verfahren zur Beurteilung haarwachstumfördernder Präparate am Beispiel einer Kombination von Hirsefruchtextrakt, L-Cystin und Calciumpanthotenat (The phototrichogram process as evaluation of hair growth stimulating compounds using as an example the combination of millet fruit extract, L-cystine, and calcium pantothenate). Magazine for Skin Diseases. 2000. 75:419-423
  2. Lenzi A, Culasso F, Gandini L, Lombardo F, Dondero F. Placebo-controlled, double-blind, cross-over trial of glutathione therapy in male infertility. Human Reproduction. 1993. 8(10):1657-1662
  3. Eskiocak S, Gozen AS, Yapar SB, Tavas F, Kilic AS, Eskiocak M. Glutathione and free sulphydryl concentrations of seminal plasma in healthy medical students during and after exam stress. Human Reproduction. 20(9):2595-2600
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