The office manager for Tunisia's president suffered a headache and short-term vision loss after opening a suspect envelope on Monday, the presidency said on Thursday.
The office manager was transferred to a military hospital. Another presidential employee also suffered a headache after the envelope was opened, it said in a statement.
Reports emerged on social media on Wednesday saying President Kais Saied had been sent a letter that may have contained poison.
The statement said Saied was in good health and that the presidency had not commented earlier in order to prevent public alarm.
A source at the presidency told Reuters on Wednesday that a suspicious letter had arrived at Saied's office and that an investigation was underway.