The commonest side-effects experienced by people taking nevirapine (Viramune) are rash, nausea, fatigue, headache, vomiting, diarrhoea, abdominal pain and muscle pain.

Approximately 16% of people starting nevirapine get a rash in the form of red blotches, itchy lumps or speckles on the skin. This usually appears after one to four weeks of treatment. In most cases the rash goes away after two to four weeks on the drug, and thereafter most people experience very few or no side-effects.

The rash can be treated in many cases with anti-histamines. However about 7% of people taking nevirapine develop a more serious rash, which can occasionally require hospitalisation. Some cases of Stevens-Johnson syndrome have also reported. The rash usually goes away upon discontinuing the drug, but at least one patient has needed a skin graft. Patients experiencing severe rash or a rash accompanied by fever, blistering, sores in the mouth, conjunctivitis, facial swelling, muscle or joint aches or general malaise should consult a doctor, who may advise them to stop taking nevirapine.

Concurrent treatment with antihistamines during the first two weeks of nevirapine therapy has also been shown to reduce the risk of rash^[1]. However, treatment with the corticosteroid prednisolone has no effect on the number of patients experiencing rash, and can increase its severity^[2][3].

Beginning treatment with nevirapine at the same time as abacavir (Ziagen) is not recommended as both drugs can cause rashes, and it can be difficult to tell which drug is causing the reaction.

Women are at greater risk of developing the mild and severe forms of rash associated with nevirapine than men^[4][5][6][7]. Thus, women who commence treatment with nevirapine should watch carefully for signs of rash. A small study has also identified a genetic variant in a human leukocyte antigen gene that may increase the risk of hypersensitivity to nevirapine, including rash and liver problems^[8].

In addition to rash, liver toxicity can be a problem in patients beginning nevirapine^{[9][10][11][12]}. The greatest risk of liver toxicity occurs in the first six weeks of treatment and patients should receive liver enzyme monitoring every two weeks during the first month of treatment and monthly thereafter for the first 18 weeks of treatment. Less than 1% of patients in clinical trials have stopped nevirapine treatment due to liver toxicity. While elevated liver enzymes are more common in patients with hepatitis co-infection, these patients are not at increased risk of liver toxicity.

If any moderate or severe abnormalities in liver enzymes occur, nevirapine should be interrupted, and should only be restarted when liver enzyme levels return to baseline. Nevirapine treatment should be restarted at an initial dose of 200mg a day and liver enzymes should be closely monitored. The dose should be increased to 400mg a day with caution after extended monitoring.

During 2000, both the European Agency for the Evaluation of Medicinal Products and the United States manufacturer issued warnings regarding nevirapine-related liver toxicity. In early 2004, Boehringer Ingelheim updated the safety warning, stating that women with CD4 counts above 250 cells/mm³ are at twelve fold greater risk of nevirapine-related liver toxicity than men. Women with CD4 cell counts above this level should start nevirapine with caution, as should men with CD4 cell counts above 400 cells/mm³. This may be of particular relevance to people taking nevirapine as part of a post-exposure prophylaxis (PEP) regimen to prevent HIV infection^[13]. Pregnant women seem to be at particular risk of developing liver toxicity when starting nevirapine treatment^[14][15]. It is also less common in people with a genetic variation in the multidrug resistance-1 gene^[16].

Symptoms of liver toxicity include nausea, loss of appetite, fatigue, liver tenderness or swelling, malaise, yellowing of the whites of the eyes, dark greenish / brown urine, yellowing of the skin (jaundice), and greyish or white stools.

High-density lipoprotein (HDL or ‘good’) cholesterol may rise in people taking nevirapine^[17]. Nevirapine appears to have a better lipid profile than efavirenz^[18][19].