Updated

An investigation into the deaths of four California women who died after taking RU-486 (search) has added extra fuel to the fiery debate over the so-called chemical abortion pill.

"The FDA should have never approved this dangerous drug. It has one purpose only — that is to kill a human being — and now we are finding out that it is killing two human beings, the baby and the mother," said Wendy Wright, policy director of the anti-abortion Concerned Women for America (search).

That charge has led to complaints that issues surrounding RU-486 seem to be more about politics than health.

"It has been FDA-approved at a significant delay from many other Western nations because of the politics involved. That said, it was approved because it's incredibly safe, it's effective and has a very low risk of adverse events," said Dr. Deborah Nucatola (search) of the University of Southern California medical school.

While RU-486 opponents suspect under-reporting of dangerous side effects, supporters point out that, despite the investigation, there is no proven relationship between the drugs and the infections that killed the four women. Lack of proper medical supervision while taking the drugs may have figured in the deaths.

"Four-hundred and sixty-thousand American women have already used it safely and effectively since September of 2000 when it was approved by the FDA," said Vicki Saporta of the National Abortion Federation.

The chemical abortion procedure actually involves two drugs. Mifeprex (search), which stops the pregnancy, is taken orally in a doctor's office up to 49 days after a woman becomes pregnant. Several days later Misoprostol (search), which causes contractions of the uterus, is administered. Misoprostol is the drug under investigation.

Legislation to ban chemical abortion — often also referred to as "medical abortion" — has been proposed in California. Holly's Law is named after the first woman to die from infection after the procedure.

The fourth death was in June in Southern California. The state and federal probe is ongoing, and the FDA has issued a warning about the procedure.

Click in the video box above to watch a full report by FOX News' Adam Housley.