Three men were taken to hospital after it was believed they took a drug they bought off the internet.
The students, living in St Christopher's Close, Chichester took the Mescaline drug on Saturday (May 17) before becoming unwell.
The three men, aged 21, 18 and 20, were taken to hospital.
The 21-year-old was arrested on suspicion of possession of class A drug, supply class A drug, two counts of possession of class B, permit use of premises for supplying class A drug. He has been bailed until July 12. The other two will be talked to by officers when they have made a better recovery.
Detective Constable Ceri Spratt said: "These drugs are illegal and potentially lethal. We would urge people not to buy drugs from the internet, even so-called legal highs, and if anyone has information about the supply of these drugs to contact us immediately. If you or anyone are suffering from the effects of any drug please seek medical help immediately."