L-Cysteine HCL Monohydrate: Benefits, Side Effects & Dosage

What Is L-Cysteine HCL Monohydrate?

L-cysteine HCL monohydrate (commonly known as cysteine) is an amino acid the body uses to make proteins. Although it is produced naturally, most cysteine comes from dietary sources. Cysteine is one of the main building blocks of glutathione, a powerful antioxidant the body produces to fight off free radicals and prevent cellular damage. Without enough dietary cysteine, glutathione levels drop (x).

In addition to its antioxidant boosting effects, research shows that cysteine may have a number of other health benefits. Studies suggest that it may reduce inflammation and improve digestion (x). Cysteine may also be able to improve immune function in patients with conditions such as HIV by stimulating infection-fighting cells in the body.

Cysteine is present in most foods with high protein levels, such as chicken, legumes, spinach and eggs. However, it may only produce therapeutic benefits in higher supplemental doses. N-acetyl cysteine (NAC) is another common supplement, typically sold in capsule or powder form.

Benefits of L-Cysteine HCL Monohydrate

Fighting Inflammation

Researchers claim that cysteine may have a significant anti-inflammatory effect. Studies suggest that cysteine may be able to help reduce inflammation in ulcerative colitis patients (x). Although the research is promising, there are not enough studies to completely understand cysteine’s full anti-inflammatory effects.

Antioxidant Production

Cysteine is important for building some of the body’s most powerful antioxidants. It is one of the amino acids the body needs to build glutathione, which helps protect the body from free radicals. Cysteine has also been linked to fighting free radicals that may develop after exercising, which may help prevent inflammation and expedite recovery (x). One study analyzed patients who took cysteine supplements for one week. It led to a significant increase in antioxidant production and a subsequent drop in free radicals (x).

Digestive Support

Research further reveals that cysteine might help regulate digestion by increasing the amount of key nutrients that the body absorbs. One study specifically cited that when patients consumed large amounts of cysteine, it led to an increase in iron absorption after they ate meat (x). Iron carries oxygen throughout the body and fuels muscles. Low levels of iron can lead to anemia, a condition characterized by fatigue, weakness and pale skin.

Immune System Boost

Cysteine is crucial for producing glutathione, a powerful antioxidant, and it may give the immune system a boost. Studies claim that cysteine supplements may stimulate immune activity and lower the risk of infection in HIV patients (x).

Researchers suggest that cysteine stimulates cells that help the body fight infections naturally. Other studies argue that cysteine may be able to prevent the flu virus from spreading between cells, which could lower the risk of getting the flu and also help treat it (x).

Although the studies are promising, there is not enough research to completely understand the role that cysteine plays in the immune system. It should never be a first line therapy for immuno-suppressed patients, such as those with HIV.

Blood Sugar Regulation

High blood sugar can increase the risk of type 2 diabetes and can lead to obesity. It can also make the body less sensitive to insulin, the hormone responsible for regulating blood sugar. Studies have shown that cysteine may be an effective method to reduce inflammation in certain types of fat cells that produce insulin. Cysteine can help prevent insulin resistance by limiting damage to those cells (x). By regulating insulin, cysteine allows the body to keep blood sugar at a healthy level, which can lower the risk of diabetes and obesity. However, most studies on cysteine to regulate blood sugar use animal models, so researchers need to conduct more studies and compare them to human models to better determine its effects.

Mental Health Benefits

In addition to physical health, cysteine may also have a number of mental health benefits. Studies have shown that NAC, a form of L-cysteine, is often effective in reducing the frequency of addictive behaviors, including substance abuse (x). Other research has shown that NAC may be an effective way to reduce the severity of obsessive compulsive disorder (OCD) symptoms and anxiety, improving daily functioning and quality of life (x, x).

Although these studies are promising, there is not enough research to make definite conclusions on how cysteine may affect mental health. It is not a treatment for any mental condition and patients should not use it unless a doctor supervises directly.

Respiratory Health Support

Cysteine may be an effective treatment for some respiratory conditions because it can help remove excess mucus and clear blocked airways. Studies also infer that NAC may be an effective treatment for chronic obstructive pulmonary disease (COPD), a condition that constricts airways and makes it difficult to breathe (x). NAC reduces inflammation in the lungs and alleviates mucous overload. It can keep the airways from constricting and possibly improve overall respiratory function.

Research further attests that NAC is usually effective for people who suffer from bronchitis, a condition where the bronchial tubes are obstructed by mucous. NAC thins mucus and reduces inflammation, allowing air to pass through the bronchial tubes (x). NAC may also be beneficial for other respiratory conditions such as asthma, although researchers are still assessing how it may work (x).

Benefits of L-Cysteine HCL Monohydrate

Side Effects of Cysteine

Although L-cysteine is generally safe, there are a few common side effects that patients may experience.


Some cysteine users report headaches when they begin supplementation, but it often subsides as the body adjusts to higher cysteine levels. If the headaches remain, consider lowering the dose to see if the condition improves. If it does not, stop using the supplement (x).


Cysteine affects the central nervous system, which can cause a number of side effects, including dizziness and light-headedness especially when it interacts with other medications, such as nitroglycerine (x). If the symptoms do not improve, consider lowering or discontinuing the dose. Taking cysteine with food may help reduce the severity of side effects and prevent headaches and dizziness.


Some users also report nausea, especially on an empty stomach. Take cysteine with a meal to prevent this feeling. Patients that still feel nauseous after a few days should reduce the dose or stop using it (x).


Although it is rare, some people vomit while taking cysteine. This side effect is much more common in those who take cysteine without food. Many cysteine supplements are acidic and can cause gastrointestinal issues on an empty stomach (x).

Increased Homocysteine Levels

Regular cysteine supplementation can increase homocysteine levels in the blood. High homocysteine levels have been associated with an increased risk for heart disease (x). Patients at risk for heart disease or other cardiovascular conditions should consider having their homocysteine levels checked before taking cysteine supplements.

Interactions with Medications

Cysteine is safe to take with most medication. However, it may interact with certain classes of drugs. For example, it may enhance the effects of immunosuppressants, increasing the risk of infection. Patients that take prednisone or any other immuno-suppressant should speak to a doctor before taking cysteine supplements (x). Cysteine may also interact with common medications that treat chest pain, such as isosorbide and nitroglycerin. It may increase the side effects of those drugs, such as headaches and low blood pressure (x).



Cystinuria is a kidney condition in which the body produces high cysteine levels that build up in the urine and forms stones that get stuck in the kidneys, ureters or the bladder, commonly called kidney stones. Patients with cystinuria should avoid cysteine supplements (x, x).

Pregnancy and Breastfeeding

Cysteine may be safe during pregnancy, but it might cause side effects. Researchers have not produced enough evidence to determine whether it is safe for breastfeeding. It is best to consult a doctor (x, x).

L-Cysteine HCL Monohydrate Dosage

The recommended dosage for L-Cysteine HCL monohydrate powder is 500 mg, one to three times per day unless a physician advises a different dosage.

Why Take L-Cysteine HCL Monohydrate?

Cysteine is present in a number of different foods, including chicken, cheese, eggs and legumes.

Other amino acids in the body produce it as well, but physicians recommend that patients consume additional cysteine in their diets. Although cysteine is present in food, it may be difficult to reach doses high enough to experience therapeutic benefits. L-cysteine supplements make it easier to control dosages. Furthermore, supplements make it easier to consume consistent dosages of cysteine, which can maximize its therapeutic effects. Cysteine supplements are also more cost effective than dietary sources and they have a long shelf life with proper storage.

Cysteine is used for a wide range of specific health conditions, including respiratory illnesses and immune support. It may also offer benefits as a general health supplement by lowering inflammation and regulating blood sugar levels. Cysteine has also been credited for potential mental health benefits. It may help reduce obsessive thoughts and repetitive behaviors, as well as anxiety.

Studies show that it may improve memory and cognition. Cysteine may help regulate glutamate, which is a neurotransmitter that is important for learning and cognition. It may also be able to reduce inflammation in the brain (x).

The Bottom Line

L-cysteine HCL monohydrate is an amino acid that the body uses to build glutathione, a powerful antioxidant. It embodies a range of possible health benefits as a supplement, including fighting inflammation, regulating blood sugar and improving digestion. Studies suggest that L-cysteine might be effective for treating a wide range of respiratory conditions, including COPD, bronchitis and asthma.

Furthermore, cysteine may have a number of mental health benefits, potentially improving OCD symptoms and reducing anxiety. It may also be able to help boost memory and cognition by regulating glutamate, which is crucial for learning and brain function.

Although cysteine is generally safe, there are a few side effects that some patients may experience. Some users report nausea, dizziness and headaches. Always take the recommended dosage and report any side effects to a physician. Although cysteine may have health benefits, it is not a proper treatment for any health condition. Consult a doctor before taking supplements.

Author: BulkSupplements Staff