The US Supreme Court has unanimously rejected an effort to sharply restrict access to the abortion pill mifepristone.

The decision is a major win for pro-choice activists and comes two years after the court rescinded the nationwide guarantee to an abortion.

The justices decided the plaintiffs, a group of anti-abortion doctors and activists, did not have a legal right to sue.

Mifepristone is one of two drugs used in a medication abortion, now the most common method of terminating pregnancies in the US.

The plaintiffs, known as the Alliance for Hippocratic Medicine, had argued that federal approval for the drug should be withdrawn.

But during arguments on the case in March, several of the court’s seven justices sounded sceptical that any of the plaintiffs had suffered harm from the availability of mifepristone – which is necessary to have the legal standing to sue.

“The plaintiffs have sincere legal, moral, ideological objections to elective abortion and to FDA’s relaxed regulation”, the justices wrote in the decision, “but they failed to demonstrate” any actual injury.

The top court overturned Roe v Wade, effectively rescinding a federal right to abortion, in June 2022. Since then, 21 states have moved to restrict abortion earlier in pregnancy than the standard it set. Seventeen of those have barred the procedure at six weeks or earlier.

Medication abortion – using pills sent by mail – has quickly become an effective workaround to those bans.

The two-drug regimen was approved for use up to 10 weeks of pregnancy by the Food and Drug Administration (FDA) in 2000. A patient is first given mifepristone to induce an abortion and then misoprostol to empty the uterus.

Since 2016, the FDA has eased access to the drug and has allowed doctors to hold virtual appointments with patients and for prescriptions to be sent by mail.

Throughout two decades of use, the FDA, the American College of Obstetrics and Gynaecologists (ACOG) and other mainstream medical organisations have maintained that both mifepristone and misoprostol are safe for use.

US studies say medication abortion is about 95% effective in ending pregnancy and requires further medical follow-up less than 1% of the time.