British police say there is "nothing to suggest that Novichok" caused two people to fall ill this weekend at a restaurant in Salisbury, where earlier this year the nerve agent was used in an attempted assassination.
On Sunday evening, Wiltshire Police declared a major incident following a report that a man in his 40s and a woman in her 30s had fallen ill in the English city.
Streets were cordoned off in Salisbury after police received a call from the ambulance service to Prezzo restaurant in the city's High Street.
"We can now confirm that there is nothing to suggest that Novichok is the substance," Wiltshire police said in a statement. "Both people remain in hospital under observation."
"Due to recent events in the city and concerns that the pair had been exposed to an unknown substance, a highly precautionary approach was taken by all emergency services," it added.
In March, a former Russian spy, Sergei Skripal, and his daughter, Yulia, were found collapsed in Salisbury's city center. It was later discovered they had been exposed to the nerve agent Novichok.
They were released after weeks in hospital. However, two local residents fell ill in June after also being exposed to Novichok.
One of them, Dawn Sturgess, 44, died because of the poisoning. A murder inquiry was launched. Her partner Charlie Rowley, 45, survived after spending almost month in hospital.
The British government has accused two Russians, Alexander Petrov and Ruslan Boshirov, of attempting to murder the Skripals.
The two men accused of the attack have admitted they visited Salisbury, but say the purpose of their brief trip was to visit its historic cathedral and not to poison the Skripals.
The leaders of the United States, France, Germany and Canada have backed Britain's assessment that the two suspects were Russian military intelligence officers and that the Russian government "almost certainly" approved the attack.