Like other drugs for HIV, Efavir works by impairing the virus's ability to multiply. However, when taken alone it may prompt the virus to become resistant. Efavir is therefore always taken with at least one other HIV medication, such as Retrovir or Crixivan. Even when used properly, it may remain effective for only a limited time. Efavir is one of the growing number of drugs used to fight HIV infection. HIV, the human immunodeficiency virus, weakens the immune system until it can no longer fight off infections, leading to the fatal disease known as AIDS (acquired immune deficiency syndrome).

Like other drugs for HIV, Efavir works by impairing the virus's ability to multiply. However, when taken alone it may prompt the virus to become resistant. Efavir is therefore always taken with at least one other HIV medication, such as Retrovir or Crixivan. Even when used properly, it may remain effective for only a limited time. Efavir is one of the growing number of drugs used to fight HIV infection. HIV, the human immunodeficiency virus, weakens the immune system until it can no longer fight off infections, leading to the fatal disease known as AIDS (acquired immune deficiency syndrome).

Like other drugs for HIV, Efavir works by impairing the virus's ability to multiply. However, when taken alone it may prompt the virus to become resistant. Efavir is therefore always taken with at least one other HIV medication, such as Retrovir or Crixivan. Even when used properly, it may remain effective for only a limited time.