The supreme court decided on Friday to block a lower court ruling placing significant restrictions on the abortion drug mifepristone. The decision came in the most pivotal abortion rights case to make its way through the courts since Roe v Wade was overturned last year. More than half of abortions in the US are completed using pills. The case was brought by a conservative Christian legal group arguing the Federal Drug Administration improperly approved mifepristone more than 23 years ago. The Biden administration vigorously defended the FDA against the charge, emphasizing its rigorous safety reviews of the drug and the potential for regulatory chaos if plaintiffs and judges not versed in scientific and medical arguments begin to undermine the agency’s decision-making. The case has moved quickly through the courts in recent weeks, as contradicting rulings have thrown the future of the drug into question. In early April, a federal judge in Texas, Matthew Kacsmaryk, first ruled in the lawsuit brought by a coalition of anti-abortion groups to suspend the FDA’s 23-year old authorization of mifepristone entirely, writing that the agency wrongly approved the drug. Following a challenge by the Biden administration in the fifth circuit court of appeals, a divided three-judge panel said the drug’s approval could stand, but imposed restrictions on it, limiting its use to seven weeks of pregnancy instead of the current 10-week limit, and banning delivery of the pill by mail. The Biden administration then asked the supreme court to intervene before the restrictions went into effect. Justice Samuel Alito twice stayed the lower court ruling, keeping access to mifepristone unaltered while the court deliberated. Complicating matters, another federal judge issued a ruling directly contradicting Kacsmaryk’s, ordering the FDA to refrain from making any changes to the availability of mifepristone in 18 jurisdictions. That judge – Judge Thomas O Rice, in Washington – reaffirmed that order after the fifth circuit’s ruling. Both the Biden administration and pharmaceutical companies have warned of regulatory chaos around drug approvals, should the supreme court allow the restrictions on mifepristone to go into effect. “If this ruling were to stand, then there will be virtually no prescription, approved by the FDA, that would be safe from these kinds of political, ideological attacks,” President Biden said in a written statement following the Kacsmaryk’s decision in early April. The US vice-president, Kamala Harris, echoed the point in a statement responding to the appellate decision: “If this decision stands, no medication – from chemotherapy drugs, to asthma medicine, to blood pressure pills, to insulin –would be safe from attacks.”