Image caption There is new evidence that ketamine can cause severe bladder damage

The drug ketamine should be upgraded from a Class C drug to Class B, government advisers have recommended.

The Advisory Council on the Misuse of Drugs said new evidence had shown frequent ketamine use could cause "severe and disabling" bladder damage.

Under the new classification, illegal possession of ketamine could lead to a five-year jail sentence.

Ketamine is an anaesthetic used for operations on humans and animals that has become a popular recreational drug.

Home Office figures released in the summer showed that in the past year about 120,000 people aged 16-59 in England and Wales took ketamine, which is best known by the street names K, Special K and Vitamin K.

'Bladders removed'

Home Secretary Theresa May asked the Council to review the evidence on ketamine last year amid increased concern about its popularity and potential harm the drug can cause.

Case study "Molly", 25, is waiting for a bladder-stretching operation after damaging it by taking ketamine. "It sounds a bit strange to say you're looking forward to an operation - but I'm hoping it'll be the start of an end. "I have to go the toilet three times an hour. It takes me ages, and it's absolute agony. "The only thing that takes that away is ketamine. It's sort of like a vicious cycle. "I'm actually peeing blood - sizeable blood clots. "Ketamine being Class C is completely ridiculous. "It has not taken that long for me to completely ruin my bladder." Long-term users on the effect of ketamine

It has gathered new evidence suggesting some people are taking large amounts of ketamine every day, risking severe damage to their bladders.

In the most serious cases users have had to undergo surgery to have their bladders removed.

The council said the decision to reclassify ketamine was not unanimous, but was backed by a majority of its members.

The advisory group's chairman, Prof Les Iversen, said he was not sure if the home secretary would take their advice and reclassify the drug, saying: "I've learnt that you give advice and it's not always taken."

An upgrade from Class C to Class B means those found in possession of the drug would face up to five years in prison, up from two, and those caught supplying it up to 14 years prison or an unlimited fine.

The average prison sentence served for possession of a Class B drug in 2012 was just over two months, while people convicted of supply served an average of 17 months.

Other Class B drugs include amphetamines and cannabis.

The council also recommended that ministers consider tighter controls on the way the drug is stored by pharmacies and hospitals.

Prof David Nutt, a former government adviser, said that if rules on the legal use of ketamine were changed and it had to be kept under lock and key, vets would not be able to use the drug in the field and animals "will suffer".

He said there was no evidence the drug was being taken from clinical stores, "so there is absolutely no need for this change".

Prof Valerie Curran, professor of psychopharmacology at University College London, agreed, and added that she was pleased the medical community would be consulted before the final decision was made.

"Molly", 25, is waiting for an operation to stretch her bladder after she damaged it through ketamine use.

She said it was "agony" to go to the toilet, and there were often "sizeable blood clots" in her urine.

"Ketamine being Class C is completely ridiculous. It's not taken that long for me to completely ruin my bladder," she told the BBC's Newsbeat.

Media playback is unsupported on your device Media caption Ketamine users talk about the health problems they have experienced (first published July 2011)

First reports of ketamine being used as a recreational drug emerged soon after its release on to the market in 1965.

It gained popularity in the UK nightclub scene in the early 1990s as people bought it in the mistaken belief that it was ecstasy.

Ketamine is dose-specific, so the amount taken determines the level of effect.

It comes in various forms, most commonly as a powder, but also as a liquid and a tablet.

At low doses the user may feel euphoric, experience waves of energy, and possibly synaesthesia - sensations such as seeing sounds or hearing colours.

However, some evidence suggests that use of the drug has an effect on memory, which persists for longer than three days after use, and becomes worse for regular users of the drug.

Government figures suggest the number of ketamine-related deaths peaked at 21 in 2009, falling to six last year.