A variant of the party drug Ketamine has been licensed in the US for treatment-resistant depression.
The decision comes as the European Medicines Agency (EMA) considers a similar application, which could see British patients given the powerful anaesthetic better known as an illegal club drug.
The US Food and Drink Administration (FDA) yesterday licensed the nasal spray for use by those who have already tried at least two medications for depression, without success.
The license means patients can only receive the treatment called Spravato under medical supervision.
The EMA is expected to take a decision on a similar application by drugs firm Janssen, part of Johnson & Johnson later this year or next year. British regulators are likely to take its ruling into account before deciding whether or not to authorise use of the drug.
Clinical trials suggest it is up to 10 times more effective than current drugs in people suffering from treatment-resistant depression.
The drug comes in the form of esketamine, a mirror image of the ketamine molecule, which is far more potent.
Scientists say it is the first new drug for 35 years for depression, with no major breakthroughs since the launch of treatments like Prozac in the 1980s. Those drugs target the feel-good brain chemical serotonin, and can take weeks or months to kick in.
The new drug works differently, targeting a chemical called glutamate that is thought to restore brain connections that help relieve depression.