A pharmacist spiked the drink of a 26-year-old female friend as they worked together in a pharmacy on UNSW's Kensington campus, police allege.

Yan Chi "Anthony" Cheung, 33, was arrested at his Maroubra home in Sydney's east on Thursday morning, charged with using poison to injure or cause distress or pain.

His assistant had told Maroubra Police the day before that she suspected Mr Cheung had been placing drugs in her drink at their work, Pharmacy@UNSW.

She told police she had felt ill during shifts a number of times since last year.