Upending the conventional medical wisdom, two studies found that birth control pills do not worsen lupus and appear to be safe for the tens of thousands of women with the crippling immune disorder.

"For 30 years, we were all wrong," said Dr. Michelle Petri, lead researcher on one of the studies and director of the Lupus Center at Johns Hopkins University School of Medicine.

The studies, involving hundreds of women in the United States and Mexico, found that oral contraceptives do not increase flare-ups in women with lupus, a sometimes-fatal disease that mostly strikes women of childbearing age.

For decades doctors believed that the hormone estrogen in birth control pills could trigger flare-ups. Because of mouse experiments, a long-ago study using oral contraceptives with much more estrogen than today's pills, and the fact that lupus is mainly a disease of menstruating women, doctors had "a complete prohibition against oral contraceptives" for lupus patients, Petri said.

Forced to use less-reliable birth control methods, women with lupus ended up aborting about one-fourth of pregnancies, according to Petri.

The two studies were reported in Thursday's New England Journal of Medicine.

Lupus symptoms can range from facial rashes, joint pain and kidney inflammation to anemia, seizures and schizophrenic behavior.

In Petri's study at 14 U.S. sites, 91 women took estrogen-progestin combination pills, while 92 women in a comparison group got a placebo; all used barrier contraceptives as well. Over a year, seven women in each group had a severe lupus flare-up; each group had 1.4 mild or moderate flare-ups per year.

In the second study, conducted at the National Institute of Medical Science and Nutrition in Mexico City, 162 women were split in three groups. One got estrogen-progestin pills, the second got progestin-only pills, and the third got an intrauterine device, or IUD, without hormones. The IUD served as a sort of placebo.

Each group had similar results when it came to flare-ups, symptoms and side effects.

"Both studies clearly show that most women with lupus can take oral contraceptives safely," Petri said.

Like the women in the studies, about 90 percent of the roughly 300,000 American women with lupus have inactive or mild disease, she said.

Dr. Petros Efthimiou, a rheumatologist at University of Medicine and Dentistry of New Jersey, said more research is needed in women with moderate or severe disease.

He said the estrogen may have actually benefited the women by smoothing out the ups and downs that occur in estrogen levels during the menstrual cycle. Some doctors think estrogen peaks can trigger lupus flare-ups.

"Now we'll feel more comfortable with giving these women oral contraceptives," he said.