With lethal-injection drugs in short supply and new questions looming about their effectiveness, lawmakers in some states with the death penalty are considering bringing back relics of a more gruesome past: firing squads, electrocutions and gas chambers.

Most states abandoned those execution methods more than a generation ago, in the hope of making capital punishment more palatable to the public and to a judicial system worried about inflicting cruel and unusual punishments that violate the constitution.

But to some elected officials, the shortages of lethal drugs and the recent legal challenges around them are beginning to make lethal injection seem too vulnerable to complications.

"This isn't an attempt to time warp back into the 1850s or the wild, wild west or anything like that," said the Missouri state Republican representative, Rick Brattin, who this month proposed making firing squads an option for executions. "It's just that I foresee a problem, and I'm trying to come up with a solution that will be the most humane yet most economical for our state."

Brattin said questions about the injection drugs were sure to end up in court, delaying executions and forcing states to examine alternatives. It was unfair, he said, for relatives of murder victims to wait years, even decades, to see justice served while lawmakers and judges debated execution methods.

Like Brattin, a Wyoming lawmaker this month offered a bill allowing the firing squad. Missouri's attorney general and a state lawmaker have raised the notion of rebuilding the state's gas chamber. And a Virginia lawmaker wants to make electrocution an option if lethal-injection drugs are unavailable.

If adopted, such measures could mark a return to the days of inmates being hanged, electrocuted or shot by marksmen.

States began moving to lethal injection in the 1980s in the belief that powerful sedatives and heart-stopping drugs would replace violent spectacles with a more clinical process while limiting – if not eliminating – pain.

The total number of US executions has declined from a peak of 98 in 1999 to 39 last year. Some states have turned away from the death penalty entirely; many have cases tied up in court. And those that carry on with executions find them increasingly difficult to conduct because of the scarcity of drugs and doubts about how well they work.

In recent years, European drug makers have stopped selling the lethal chemicals to prisons because they do not want their products to be used to kill.

At least two recent executions have also raised concerns about the drugs' effectiveness. Last week an Ohio inmate, Dennis McGuire, took 26 minutes to die by injection, gasping repeatedly as he lay on a stretcher with his mouth opening and closing. And on 9 January an Oklahoma inmate, Michael Lee Wilson, uttered the final words: "I feel my whole body burning."

Missouri threw out its three-drug lethal injection procedure after it found it could no longer obtain the drugs. State officials altered the method in 2012 to use propofol, which was found in the system of Michael Jackson after he died of an overdose in 2009.

The European Union threatened to impose export limits on propofol if it were used in an execution, jeopardising the supply of a common anaesthetic used in hospitals across the US.

In October the Missouri governor, Jay Nixon, stayed the execution of a serial killer, Joseph Paul Franklin, and ordered the state's department of corrections to find an alternative drug.

Days later, the state announced it had switched to a form of pentobarbital made by a compounding pharmacy. Like other states, Missouri has refused to divulge where the drug comes from or who makes it.

Missouri has carried out two executions using pentobarbital – Franklin's, in November, and that of Allen Nicklasson, in December. Neither inmate showed outward signs of suffering, but the secrecy of the process resulted in a lawsuit and a legislative inquiry.

Michael Campbell, assistant professor of criminal justice at the University of Missouri-St Louis, said some lawmakers simply did not believe convicted murderers deserved any mercy.

"Many of these politicians are trying to tap into a more populist theme, that those who do terrible things deserve to have terrible things happen to them," Campbell said.

Richard Dieter, executive director of the Death Penalty Information Centre in Washington, DC, cautioned that there could be a backlash.

"These ideas would jeopardise the death penalty because, I think, the public reaction would be revulsion, at least from many quarters," Dieter said.

Some states already provide alternatives to lethal injection. Condemned prisoners may choose the electric chair in eight states: Alabama, Arkansas, Florida, Kentucky, Oklahoma, South Carolina, Tennessee and Virginia. An inmate named Robert Gleason Jr was the most recent to die by electrocution, in Virginia in January 2013.

Arizona, Missouri and Wyoming allow gas-chamber executions. Missouri no longer has a gas chamber but its attorney general, Chris Koster, a Democrat, and the Missouri state senator, Kurt Schaefer, a Republican, last year suggested rebuilding one. So far, there is no bill to do so.

Delaware, New Hampshire and Washington state still allow inmates to choose hanging. The last hanging in the US was of Billy Bailey in Delaware in 1996. Two prisoners in Washington state have chosen to be hanged since the 1990s – Westley Allan Dodd in 1993 and Charles Rodman Campbell in 1994.

Firing squads typically consist of five sharpshooters with rifles, one of which is loaded with a blank so the shooters do not know for sure who fired the fatal bullet. They have been used mostly for military executions.

Since the end of the civil war, there have been three civilian executions by firing squad in the US, all in Utah. Gary Gilmore uttered his famous final words – "Let's do it" – on 18 January 1977, before his execution, which ended what amounted to a 17-year national moratorium on the death penalty.

The convicted killers John Albert Taylor in 1996 and Ronnie Lee Gardner in 2010 were also put to death by firing squad.

Utah is phasing out its use, but the firing squad remains an option there for inmates sentenced prior to 3 May 2004.

Oklahoma maintains the firing squad as an option, but only if lethal injection and electrocution are deemed unconstitutional.

In Wyoming, the Republican state senator, Bruce Burns, said death by firing squad would be far less expensive than building a gas chamber. Wyoming has only one inmate on death row, a 68-year-old convicted killer called Dale Wayne Eaton. The state has not executed anyone for 22 years.

Jackson Miller, a Republican in the Virginia house of delegates, is sponsoring a bill that would allow for electrocution if lethal injection drugs were not available.