More than £100,000 has been spent buying vaping kits for inmates in Scottish jails, it has emerged.
It follows a nationwide ban on smoking in prisons which came into force at the end of November.
The Scottish Prisoner Service has given out about 7,500 of the vaping kits.
It said it would make long-term savings through improvements to the health of staff and prisoners. However, campaigners have questioned whether this is good value for money.
About 72% of inmates smoke compared with 16% of Scots in the wider population.
Responding to a Freedom of Information Request, the SPS said it expected the total cost of the vaping kit scheme to be about £150,000.
Each vaping kit supplied by the prison service - which includes a pen, a charger and a pack of three flavoured liquids - costs £14.
"It's a very positive step for the well-being of the people in our care and the people who work for us," said SPS spokesman Tom Fox.
"I think it's money well spent. The health benefits for our staff and those in our care greatly outweigh any initial cost we have introducing the programme."
The air quality in prisons has risen by an average of 80% since smoking was banned, according to the SPS.
BBC Scotland spoke to some female inmates at HMP Edinburgh who said they were not in favour of the smoking ban, but that the vaping kits made it more bearable.
"There's not been a lot of trouble, or anything like that, since the smoking ban came in, which you would expect," said one prisoner.
"And that's down to the fact we have had the vapes."
Another added: "If we didn't have the vapes, there would have been all sorts of trouble."
However, the prisoners did raise the issue of the cost of refills.
"It's costing us more money and some lassies in here can't afford that," said one.
"But at the same time, it's a good thing for our health."
Simon Clark, director of pro-smoking pressure group Forest, said he believed the prison smoking ban went too far.
"At the very least, inmates should be allowed to light up outside, in an exercise yard or designated smoking area," he said.
"Vaping may satisfy some prisoners but for many people vaping is still no substitute for smoking.
"Why not offer e-cigarettes to those who want to quit and allow them to vape in their cells, but permit designated smoking areas for those who prefer to smoke?"
Pete White, chief executive of the charity Positive Prison? Positive Futures, which campaigns for the rights of prisoners, said a black market had already developed within Scottish prisons.
"There seems to have been quite a high take up of the vaping devices supplied by the SPS and, for some people, the ban represented an opportunity to give up smoking," he said.
"But there are reports that tempers seem to be a bit shorter for some and that the black market price of tobacco, papers and lighters has rocketed.
"A half-ounce of tobacco is now reported to be on sale for over £100, papers for £15 and lighters around £50."
Inmates will be expected to pay for their own vaping pens and liquids from April this year.