A Canberra woman was hospitalised after taking a capsule that was part of a "bad batch" of a toxic drug being sold as MDMA, or ecstacy in the ACT.
The unversity-aged woman was admitted to hospital within the past five days and had been discharged by Friday afternoon.
Emergency medicine specialist Dr David Caldicott said the patient, who had presented with seizures and convulsions, would likely have died if they did not seek medical help.
Dr Caldicott said his colleagues at Calvary Hospital sent out an extremely rare "ultra alert" about the drug, which warns a recreational drug is in circulation that will likely lead to hospitalisation and death if consumed.
"We analyse a great number of substances but it is only the second time we have issued an ultra alert," Dr Caldicott said.
He said the patient was told by a dealer that the drug was MDMA. But Dr Caldicott warned one capsule - the usual amount of MDMA to taken at once - would almost certainly cause severe health consequences.
"There are plenty of drugs that are bad for you but these are incredibly bad for you," he said.
"It is frequently associated with severe headaches and indeed stroke, which is very unusual in young people," he said.
The potentially-lethal substance looks similar to brown sugar and comes in pink and clear capsules. Dr Caldicott compared it to a drug that recently caused a number of overdoses in Melbourne, but contained no MDMA.
The drugs were tested after they sent the Canberra woman to hospital with seizures, and were found to have a potent combination of fluoroamphetamine and 25CNBOMe.
"25CNBOMe is a drug that not only causes these hallucinations which people have died off because they are scared and jump off buildings, it is directly toxic," Dr Caldicott said.
"It can cause seizures, severe cardiovascular problems, arrhythmias in the heart and also seizures. Patients have been hurt and killed from both behavioural effects while hallucinating, as well as the toxicological effects on the circulation."
Dr Caldicott said while no one else had presented to the emergency department admitting to taking the drug, it was difficult to determine whether anyone else from Canberra had been affected.
"It is entirely possible that people were unwell and didn't come to emergency departments," he said.
But he urged anyone who suspected they had consumed the drug to seek immediate medical help, and anyone in possession of it to dispose of it.
Dr Caldicott said the 25CNBOMe chemical was falsely referred to as synthetic LSD but was more dangerous.
Detective Sergeant Morgwn Saunders, of ACT Policing, said the find was a simple reminder of the dangers of drug use.
"There is no such thing as a safe illicit drug," he said.
"Any substance that has not been prescribed by a medical professional has risks with it, including hospitalisation or death."
For drug advice people can call the Alcohol and Other Drugs Services 24 Hour Helpline on 6207 9977.
If members of the community have any information regarding the purchasing, selling or manufacturing of illegal drugs they should call ACT Policing Operations on 131 444 or Crime Stoppers on 1800 333 000. Information can be provided anonymously.