The 150 pellets had an estimated street value of $2.7 million, police said.
The 30-year-old man showed symptoms of an overdose when he arrived at Rome's Leonardo da Vinci airport from Sao Paulo, Brazil, police said in a statement. Some of the pellets had broken in his stomach, they said.
The statement said the man was taken to a hospital and then put under arrest. It did not specify when the incident occurred.