Istanbul Grill in High Street, Bognor Regis, was stripped of its licences and has been closed since the incident on December 29.
Sussex Police has confirmed two local men, aged 30 and 42, arrested on suspicion of administering poison with intent to endanger life or inflict grievous bodily harm, remain released under investigation.
"The substance in a capsule found in a kebab has been forensically examined and has been found not to contain a controlled drug," a police spokesman said.
"It is emphasised that the substance was found within only one kebab, purchased by one customer."
Police said the capsules found in the shop were a 'different substance' and' were also not controlled drugs'.
The spokesman added: "The capsules in the kebab and in the shop contained legitimate medication and enquiries continue to establish their potential health impacts, if any, and whether or not any offences have been committed.
"Anyone with any information relevant to the investigation can contact the police online at https://www.sussex.police.uk/contact/af/contact-us/ or by calling 101, quoting Operation Enzo.