A BAD batch of ecstasy in circulation on the weekend caused users to strip and swim in the Torrens, lick floors, rub themselves on the road and - in one case - act like a chicken in a taxi, police revealed today.

A total of 21 were taken to hospital over the weekend displaying overdose symptoms suspected to be from the bad ecstasy tablets.

One man, 21, remains in the Royal Adelaide Hospital in a critical condition.

SA Police Superintendent Anthony Fioravanti said emergency services were particularly busy in the city on Saturday night.

"Police and health services had a busier than usual night as a result of reports people had taken ecstasy tablets that were from a bad batch," he said.

"The normal effects of ecstasy are a feeling of euphoria, heightened arousal and an emotional effect and an increase in body temperature.

"While some of these effects were evident, there was an increase in aggression, rather than a feeling of euphoria.

"This resulted in an increase of reported fights in the city and had the illicit drug users displaying psychotic, extreme and bizarre behaviour."

Among the bizarre behaviour witnessed in the city on Saturday night was:

A PERSON stripping down and swimming naked in the river Torrens.

A PERSON licking the floor of a nightclub.

PEOPLE disrobing and rubbing themselves on the bitumen.

A PERSON acting like a chicken in the back of a taxi.

"They were extreme and bizarre behaviour," Supt Fioravanti said.

Early on Sunday, police arrested a man, 21, at North Adelaide and charged him with trafficking a controlled drug.

He was allegedly in the possession of 33 ecstasy tablets and $900 cash and he has been bailed to appear in court at a later date.

Among the drugs seized were three varieties of ecstasy - Green Mitsubishi, Pink Superman and Yellow Ferrari.

These pills are currently being analysed.

"We do not know if the overdoses that occurred are linked with the drugs that he sold," Supt Fioravanti said.

"We do know that there have been a number of different ecstasy tablets taken but not all those were the same as those that we found in the possession of the male offender.

"From what we've been told so far, we believe that they have been purchased from nightclubs within the CBD, however we haven't ascertained where all of them were purchased at this point."

Supt Fioravanti said Saturday was a particularly violent night in the city.

"I was talking to one of the patrol Sergeants and they just said that there were a lot more fights than they normally have," he said.

"While they didn't count how many they were, they just realised there was a lot more happening."

The 21 people affected were a mix of men and women predominately aged 18-25.

Supt Fioravanti said drug dealers were preying on young users in nightclubs.

"We will be continuing with our high visible presence," he said.

"We will be running dog operations, which we do within the CBD anyway and we will definitely be increasing the number of police in the city to try and deal with this incident."

South Australian Ambulance Service operations manager Anthony Pryzibilla said crews were kept very busy in the city.

"It was a particularly busy night in the CBD across the whole area as a result of a whole range of different things - assault, drug taking as well as alcohol intoxication," he said.

We do get a lot of transports out of the city to the hospitals as a result of assaults, alcohol and drug taking.

"When there are increases and spikes in this it just puts further burdens on our resources."

Mr Pryzibilla said the health dangers of ecstasy ranged from overheating and dehydration through to seizure and even death.

He said the bizarre behaviours reported in the city were not entirely uncommon.

"Ecstasy has a chemical compound in it that produces a hullicenegen effect so it can result in a range of different behaviours so it's not unusual that the behaviours that have been reported have been linked to ecstasy," he said.

Mr Pryzibilla said users or friends of users should not hesitate to call an ambulance.

"If one of your friends has taken ecstasy and you're concerned about them and they are displaying abnormal behaviours don't hesitate to call triple-0," he said.

"You don't need to be fearful that the police will attend when you call triple-0.

Mr Pryzibilla said police would only attend a call out if there was a death or if the ambulance crew requested them because of fears for their safety.

Anyone with information about illegal drugs is asked to call Crime Stoppers on 1800 333 000, or online at www.sa.crimestoppers.com.au.