Paramedics were called to a shopping centre at around 7pm on Monday night, where five men and one women were spotted looking "messy" according to Swedish newspaper Dagens Nyheter.
The young people, who police say were "born in the early 90s", appeared to have taken overdoses of Spice.
Spice contains the same active element as natural marijuana, but is far more toxic.
A spokesperson for Sahlgrenska University Hospital told the newspaper that one of the patients has now been released, but five remain in hospital, four in a serious condition.
Spice has been a hot topic in the Swedish media in recent weeks, since the deaths of a 22-year-old man and an 18-year-old man in separate cases following what witnesses and police described as overdoses.
Earlier this month Sweden asked the European Union for the right to speed up a ban on substances contained in the synthetic marijuana called Spice after two apparent fatal overdoses.
Several other countries have already tried unsuccessfully to stop the sale of synthetic marijuana, which is supposed to be burned like incense rather than smoked.
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