A drug charity today issued a safety guide for ecstasy users that advises them to "home test" pills before taking them.

However some medical experts have branded the guidelines as irresponsible.

It comes after a teenage girl was left fighting for her life, and three of her pals were rushed to hospital, amid fears they took ecstasy.

Amy Thomson, 16, became unwell at a property in Knightswood.

Health chiefs and senior police officers warned party-goers to stay clear of the drug or risk serious harm.

Drugs charity The Loop is now advising clubbers to take the "crush-dab-wait" test at home.

And the advice also issues a guide on how to do it.

It says: "There is a particular concern relating to the variations in purity, shape, size and density of MDMA crystals.

"However, meaning that it is difficult for users to guess consistently and accurately how much they are taking.

"Therefore we are encouraging users not to take whole crystals of MDMA.

"Instead users should think carefully about how to moderate the amount of MDMA they take with the advice to crush up crystals into a fine powder, lick their finger tip and dab the powder to consume a small amount (approximately 70-100mg of MDMA, the same as contained in an average pill and an average dose for an average sized person) then wait one to two hours for the effects before considering taking more."

One doctor, who asked to remain anonymous, said: ""I do think offering guidance of how to test a drug, which police and doctors have warned people against using, is irresponsible."

The doctor added: "It's very difficult to strike a balance on the issue of drug taking.

"In a perfect world, no one would take drugs and everyone would stay safe.

"However, we don't live in a perfect and we have to accept that people will take drugs.

Amy, 16, remains in a "critical but stable" condition in hospital.

Three other girls at the house, aged 15, 17, and 18, were treated at hospital after showing symptoms consistent with drug misuse.

Police are carrying out investigations into the Knightswood incident, which took place earlier this month.

A 33-year-old man and two women, aged 17 and 18, have been reported to prosecutors in connection with alleged drugs offences.

Dr Richard Stevenson, Consultant in Emergency Medicine, NHS Greater Glasgow and Clyde added: "The inherent dangers associated with taking recreational drugs should not be underestimated.

"Anyone who feels unwell, or knows anyone who appears unwell after taking these substances should seek medical treatment as soon as possible.

"A description or if possible the substance or tablet taken brought with the patient to the department to assist in treatment would also be helpful."

Warnings over potent party pills were issued by police following the collapse of the 16-year-old girl.

Detective Inspector Michael Miller, Police Scotland’s National Drug Co-ordinator said: "These drugs are potent and you are putting your health at risk if you take ecstasy.

"I cannot emphasise enough that consuming MDMA with alcohol or any other drug increases the risks significantly."

The "crush-dab-wait" advice from The Loop adds: "Obviously all drugs are potentially dangerous and The Loop do not encourage or condone any drug use."

Fiona Measham, co-Director of The Loop, said: "My research shows that MDMA crystal remains the most popular party drug amongst festival goers and clubbers but purity and contents can vary considerably in illegal markets.

"When purity increases it takes a while for behaviours to readjust and we often see more problems. We want to keep people safe and advice as simple as "crush-dab-wait" could save lives."