Former Russian spy Alexander Litvinenko died in agony in November 2006 three weeks after drinking tea laced with highly radioactive polonium-210 at a London hotel.
A British inquiry in January 2016 accused Moscow of the poisoning, which it denied.
Pyotr Verzilov, associate punk group Pussy Riot
Pyotr Verzilov, an anti-Kremlin activist and associate of the punk group Pussy Riot was admitted to hospital in Moscow on September 14, 2018, suffering from apparent poisoning from medical drugs.
He was quickly flown to Germany where doctors said poisoning was "highly plausible".
Verzilov's estranged wife, Pussy Riot's Nadezhda Tolokonnikova, said the suspected poisoning was "probably an assassination attempt, if not it was an intimidation."
After he is was discharged from hospital on September 26, Verzilov said he was "convinced" that he was poisoned by Russia's secret service.
Verzilov was unconscious when he was brought to Berlin four days after falling ill but recovered after being treated at the Charite.
It was Verzilov who asked Bizilj for help transporting Navalny to Germany, according to the NGO Cinema for Peace foundation.
Massive amount of dioxin
In September 2004 Ukrainian politician Viktor Yushchenko, campaigning against a Russian-backed candidate for the presidency, fell seriously ill.
Tests in an Austrian clinic found that he had ingested a massive amount of dioxin. He survived and went on to win the election, but his face was left bloated and pockmarked.
His supporters accused the Russian secret service of involvement.
Toxic nerve agent Novichok
In March 2018 former Russian double agent Sergei Skripal and his adult daughter were found unconscious on a bench in the southern English city of Salisbury and hospitalised in critical condition.
Police said they have were poisoned with the highly toxic nerve agent Novichok. London accused Moscow of wanting to kill the ex-agent for his work with European intelligence agencies. The Kremlin denied the charges.
The Skripals survived but the case became one of the biggest irritants in Britain's relations with Russia.
In June, British counterterrorism police appealed for more information about the attack, which it blamed on two Russian security service officers who had allegedly entered Britain using false passports. Russia continues to deny the claims.
Navalny loses consciousness
In the latest case, Navalny a 44-year-old lawyer and anti-corruption campaigner who is among President Vladimir Putin's fiercest critics was hospitalised in the city of Omsk after he lost consciousness while on a flight and his plane made an emergency landing.
Traces of industrial chemical substances
According to Reuters, Alexander Murakhovsky, the head doctor at Omsk hospital where Navalny was being treated had said that traces of industrial chemical substances were found on Navalny's clothes and fingers.
Alexei Navalny and Vladimir Putin
Alexei Navalny and Vladimir Putin
Navalny the star
Navalny has won a young fan base through viral videos exposing corruption among the elites and has more than two million followers on Twitter.
He has grabbed attention with his uncompromising rhetoric and coined phrases such as the "party of crooks and thieves" to slam the ruling United Russia party.
In 2011, the anti-corruption blogger led mass protests when tens of thousands took to the streets of Moscow to protest against vote-rigging in parliamentary elections.
Two years later the father-of-two stood for Moscow mayor, coming second against Putin ally Sergei Sobyanin.