This fact sheet is currently under review.
NAC (N-acetyl-cysteine) is a supplement used by people with HIV, usually as part of an antioxidant regimen. NAC is usually taken two or three times daily and is available in capsule and tablet forms in some health food stores. NAC is also available by prescription in liquid form from pharmacies.
What is NAC?
NAC is a supplement used by people living with HIV. NAC stands for N-acetyl-cysteine and is similar to the amino acid cysteine. Taking NAC helps to increase levels of the protective compound glutathione (GSH) in the body.
How does NAC work?
Before explaining how NAC works, we first need to give you some background information about GSH.
GSH is a compound that the body makes using various nutrients including the amino acid cysteine. GSH is the body's chief protector from the damage caused by toxic substances. Results from a number of studies suggest that in people with HIV the demand by the body for GSH exceeds the supply. Less-than-normal levels of GSH may result in impaired performance by cells of the immune system and perhaps increased sensitivity to the toxic effects of some drugs. When there is not enough cysteine available to make GSH, the body tears down muscles, which are rich in protein, to find the nutrients needed to make GSH. NAC works by acting as a source of cysteine and stimulating the production of GSH.
Why do people with HIV use NAC?
In the late 1980s, researchers found that people with HIV were likely to have higher-than-normal levels of highly active compounds called "free radicals." These compounds damage cells in much the same way that rust damages a car. Some people with HIV take NAC as part of an antioxidant regimen to help counter the damaging effects of high levels of free radicals. NAC continues to be studied in clinical trials with HIV-positive participants such as the Maintain study in Canada.
In laboratory experiments with cells and viruses, very high concentrations of NAC appear to reduce production of HIV. However, to achieve this concentration in the blood of people, large doses of NAC—5 grams every six hours—would have to be taken. In one short clinical trial, Norwegian researchers gave HIV-positive subjects two antioxidants: high-dose NAC (as listed previously) and vitamin C — 3 grams every six hours. These two antioxidants resulted in a modest decrease in viral load (less than one log). Unfortunately, taking large doses of antioxidants every six hours is not practical for most people with HIV over the long term. Moreover, such high doses of NAC are likely to cause nausea, vomiting and possibly diarrhea. Now that potent anti-HIV therapy (commonly called ART or HAART) is available in high-income countries, few people with HIV would consider intensive NAC therapy a suitable and practical option for lowering levels of HIV in their blood.
3. To maintain GSH, protein and muscle mass
HIV-positive people—whether or not they are taking HAART—can experience a loss of critical sulfur-containing amino acids, such as cysteine and methionine. Supplements of NAC may be able to replace lost cysteine, help maintain protein levels and possibly reduce muscle wasting. Together, all of these potential benefits may explain why one American study found that supplements of NAC—an average of 4 grams daily—prolonged survival for up to three years in the time before HAART was widely available. That study was the impetus for the widespread use of NAC by HIV-positive people and so it may be useful to briefly review findings from that study.
In the early 1990s, researchers at Stanford University in California conducted an eight-week randomized, placebo-controlled study of NAC in HIV-positive people. The dose of NAC used was about 4,400 mg daily. After the initial eight weeks, all participants were offered NAC for six months. Researchers collected data on the survival of participants for several years after they stopped using NAC. They found that this supplement significantly increased GSH levels within CD4+ cells. However, NAC did not significantly raise CD4+ cell counts. The data also suggested that people who used NAC were twice as likely to survive over the next two years compared to people who did not ever use NAC. At the time of the study, powerful anti-HIV drugs such as protease inhibitors were not available and most participants used AZT (zidovudine, Retrovir) with or without another nuke (nucleoside analogue). Due to the study design, firm conclusions about the effect of NAC on survival cannot be drawn and it is important to note that a large proportion of NAC users did eventually die. However, the trial did heighten interest in the use of antioxidants.
Researchers in Montreal also tested whey protein concentrates, which are rich in cysteine, in HIV-positive volunteers and found that they improved weight. In the time before ART was available, a sustained increase in weight was unusual in HIV-positive people.
4. To protect the liver and kidneys from the toxicity of Tylenol (acetaminophen) and other drugs
In some people, the pain reliever Tylenol (acetaminophen) can be toxic to the liver and kidneys even when used within normal doses. Use of NAC may help to reduce this problem. People with HIV who also have hepatitis sometimes use NAC, which may help to reduce liver injury that results from hepatitis or medications.
The medication tenofovir (Viread and in Truvada, Atripla and Complera) can sometimes affect the health of the kidneys of some HIV-positive people. Whether or not NAC can help decrease the risk of this damage has not been tested in studies.
5. Recovery from addiction
NAC is being studied for the treatment of addiction disorders.
At high doses, NAC may cause the following symptoms in some people:
- abdominal discomfort
In lab experiments with cells, high concentrations of NAC can weaken some activities of the immune system. There have been no studies of this in people.
If you are taking antibiotics, NAC should not be taken, as it will weaken their beneficial effects.
The best dose of NAC for people with HIV is not clear, but reviewing the data from clinical trials in people with HIV may be useful. In the previously mentioned American study, use of about 4 grams per day of NAC was associated with improved survival. However, anecdotal reports suggest that taking such large doses of NAC for prolonged periods could cause abdominal discomfort, nausea, vomiting and diarrhea.
According to results from two German studies, a dose of 3 grams every other day is effective at increasing GSH levels and does not appear to cause toxicity. Alternatively, some people with HIV take smaller doses of NAC, between 500 to 1,000 mg, twice daily.
Taking NAC with meals may reduce nausea. The manufacturer of the liquid form of NAC suggests that when it is taken in high doses it can be mixed with cola drinks or fruit juice to reduce the risk of nausea.
In drug stores, NAC is available in liquid form with a prescription and sold under the brand name Mucomyst. Health food stores may sell NAC in capsule form.
Author: Hosein SR
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Author(s): Hosein SR