Executions in the US have been postponed because of a shortage of one of the drugs used in lethal injections.

Several of the 35 states that inject are either rushing to find sodium thiopental – an anaesthetic that makes the condemned inmate unconscious – or considering using another drug. But both routes are strewn with legal or ethical roadblocks.

The shortage delayed an Oklahoma execution last month and led Kentucky’s governor to postpone the signing of death warrants for two inmates.

Arizona is trying to get its hands on the drug in time for its next execution, in late October. California said the shortage will force it to stop executions on Friday, three hours after an inmate is scheduled to die, when its stock expires.

The sole US manufacturer, Hospira, has blamed the shortage on problems with its raw-material suppliers and said new batches of sodium thiopental will not be available until January at the earliest.

Nine states have a total of 17 executions scheduled between now and the end of January, including Missouri, Ohio, Oklahoma, Tennessee and Texas.

“We are working to get it back onto the market for our customers as soon as possible,” a Hospira spokesman said.

But at least one death penalty expert was sceptical of the explanation, noting that the company has made it clear it objects to using its drugs for executions. Hospira also makes the two other chemicals used in lethal injections.

Sodium thiopental is a barbiturate, used primarily to anaesthetise surgical patients and induce medical comas. It is also used to help terminally ill people commit suicide and sometimes to put down animals.

Thirty-three of the states that have lethal injection employ the three-drug combination that was created in the 1970s: First, sodium thiopental is given by syringe to put the inmate to sleep. Then two other drugs are administered: pancuronium bromide, which paralyses muscles, and potassium chloride, which stops the heart.

Ohio and Washington use just one drug to carry out executions: a single, extra-large dose of sodium thiopental.

Switching to another anaesthetic would be difficult for some states. Some, like California, Missouri and Kentucky, adopted their execution procedures after lengthy court proceedings, and changing drugs could take time and invite lawsuits.