The distinctive triangle-shaped ‘blue superman’ pills caused a mass overdose of 11 people last weekend and "several" more people have been hospitalised after taking the pills in Newcastle this week.

Buyers may know they're getting a drug.

But what they don't know is that the drug they are getting is the potent central nervous system depressant alprazolam, or Xanax, not MDMA.

Health authorities have issued a second alert this week after several more patients were admitted to Hunter emergency departments after taking 'blue superman' pills since Tuesday.

Pills taken by people who thought they took something else.

Fairfax Media can reveal that testing of the dangerous new pills at the Forensic and Analytical Science Service laboratory in Sydney has found they are not MDMA.

The senior staff specialist addiction medicine, director alcohol and drug unit, Calvary Mater Newcastle and Hunter New England Health, Dr Craig Sadler, said the pills were addictive and potentially very dangerous.

“We are talking about a potent and fast-acting form of benzodiazepine,” he said.

“This particular supply of illicit pills is being sold as something that it is not.”

Alprazolam is used as an anti-anxiety medication or sedative and belongs to the same group of drugs as Valium.

When mixed with alcohol, another depressant, it can be extremely dangerous.

Hospital staff reported patients who had taken the ‘blue superman’ pills declined rapidly and suffered varying levels of consciousness.

At least one suffered seizures.

Dr Sadler said all patients recovered and were discharged from hospital.

He warned anyone against taking the pills and said people who took party drugs and felt unwell should seek medical help immediately.

“It is very real problem if people are taking these pills thinking they are a stimulant,” he said.

“We want people to aware that what they are being sold, is not what the pills are. They should not be taken.”

At least 11 party goers were taken to Calvary Mater Newcastle and John Hunter Hospital emergency departments between Friday and Monday nights after taking the pills. 

The patients, ten men and one woman, were aged between 18 and 34. 

The exact number is not known, but several other people were treated in Hunter hospitals since Tuesday after taking the pills.

Police urged anyone with information about the pills to call Crime Stoppers on 1800 333 000.