N-Acetyl Cysteine (NAC) for Lupus (SLE)

N-acetylcysteine (NAC) has been tested in two randomised trials in adults with systemic lupus erythematosus (SLE). In a US pilot of 36 patients, the 2.4 g and 4.8 g a day groups, analysed together, saw SLEDAI and BILAG disease-activity scores and fatigue fall over 3 months, while 1.2 g a day and placebo did not change disease activity [1]. In an Iranian trial of 80 patients, 1,800 mg a day for 3 months left BILAG and SLEDAI scores lower than in patients on their usual therapy alone [2].

Both results point the same way, but both trials were small and short. The Iranian control group got no placebo, the US results pool two doses, and neither trial counted flares, steroid use or long-term kidney damage. NAC is a reasonable thing to discuss with a rheumatologist as an add-on, not a treatment in its own right.

NAC supplies cysteine, the building block that limits how much glutathione, a key antioxidant, the body can make. In lupus, T cells are short of glutathione, their mitochondria show abnormal membrane potential, and mTOR, a growth signal that drives abnormal T-cell behaviour, is overactive. In the US trial NAC changed T-cell mitochondrial membrane potential, lowered mTOR activity (P = 0.0009), raised FoxP3 in CD4+CD25+ T cells and reduced anti-DNA antibody production (P = 0.049) [1].

Follow-up work from the same group found lupus lymphocytes burn extra oxygen through mitochondrial complex I, which NAC dampened in the lab [5]. In blood samples from the trial, NAC lowered kynurenine relative to placebo, a metabolite that switched on mTOR in lab-grown immune cells [4]. A review co-written by the trial's senior investigator ties these findings together [6].

Most of this work comes from one laboratory and measures cells and metabolites, not symptoms. Lower mTOR activity or kynurenine shows that NAC reaches the pathways linked to lupus, not that a supplement prevents flares or protects the kidneys.

A small uncontrolled study also reported better blood-vessel function and lower CRP after NAC in lupus [7], but it gives no dose, duration or randomisation in its abstract. Only larger clinical trials can show whether these changes matter to patients.

The US trial compared 1.2, 2.4 and 4.8 g of NAC a day for 3 months. Only the 2.4 g and 4.8 g groups, analysed together, showed lower disease activity, everyone tolerated up to 2.4 g, and a third of patients on 4.8 g had reversible nausea [1]. The Iranian trial used 1,800 mg a day, taken as three doses 8 hours apart, for 3 months [2].

The US result is for the 2.4 g and 4.8 g groups combined, so neither dose was shown to work on its own; 1.8 g a day is the only dose tested alone, and doses up to 2.4 g a day were well tolerated. Nothing is known about use beyond 3 months in lupus, and in both trials NAC was added to standard treatment. NAC is a question for your rheumatologist, not a swap for prescribed treatment [10].

In 2012, 36 adults with SLE were randomised to placebo or NAC at 1.2, 2.4 or 4.8 g a day for 3 months, with disease activity scored monthly and again a month after stopping. Placebo and 1.2 g did not change disease activity. Taken together, the 2.4 and 4.8 g groups had lower SLEDAI scores at months 1, 2, 3 and 4 (P = 0.0007 at month 1), lower BILAG scores at months 1 and 3, and lower fatigue scores at months 2 and 3 [1].

The abstract reports these changes for the pooled higher-dose groups rather than as a head-to-head comparison with placebo, and each arm held only about nine people. A secondary analysis of 24 of these patients found self-reported attention-deficit scores, which tracked with fatigue and disease activity, fell on NAC compared with placebo (P = 0.037) [3].

In 2023, 80 adults with SLE were randomised to NAC 1,800 mg a day or to their normal therapies for 3 months. BILAG (P = 0.023) and SLEDAI (P = 0.034) fell from baseline on NAC, and both were lower than in the control group at 3 months (P = 0.021 and P = 0.030). Within the NAC group, organ scores improved from baseline in the skin, nervous system, joints, heart and lungs, kidneys and blood vessels, CH50 complement rose, and no adverse events were reported [2].

The trial is described as double-blind, but the abstract says controls received their normal therapies and mentions no placebo, so patients and assessors may have known who took NAC. Subjective scores are especially open to that bias. It is, however, an independent result from a different group and country.

No trial has lasted longer than 3 months, enrolled more than 80 people, or counted flares, steroid doses or organ damage; the only kidney data are a within-group fall in the renal BILAG score in the Iranian trial [2]. For lupus nephritis there is only a single case report [8], and a review of non-immunosuppressive add-ons treats NAC as a candidate to explore, not an established therapy [9]. A 2022 review co-written by the US trial's senior investigator says a longer trial is being pursued [6].

For other supplements studied in lupus, see vitamin D for lupus and omega-3 for lupus.

NAC was well tolerated in both lupus trials: everyone tolerated up to 2.4 g a day in the US trial, with reversible nausea in a third of those on 4.8 g [1], and no adverse events were reported on 1,800 mg a day [2]. The oral acetylcysteine label lists nausea, vomiting and other stomach symptoms, and, rarely, rash or hives; NAC should be stopped if an allergic reaction appears [11].

The label also advises that people at risk of stomach bleeding, such as those with peptic ulcers or oesophageal varices, need their risk weighed before oral NAC, and inhaled acetylcysteine occasionally and unpredictably triggers bronchospasm, including in people with asthmatic bronchitis. Animal studies found no harm to the fetus, but there are no adequate controlled studies in pregnant women, and it is not known whether NAC passes into breast milk [11].

No interactions between NAC and lupus medicines were reported in the trials, which added NAC to patients' usual treatment [1][2], but none was designed to look for them. Standard care follows the EULAR recommendations: hydroxychloroquine for all patients, steroids kept as low as possible, and immunosuppressants or biologics such as belimumab or anifrolumab when needed [10].

Because both lupus and its treatments are monitored closely, tell your rheumatologist before starting NAC so any change in your tests can be interpreted correctly.