Constable Aaron Redaelli said a woman presented the prescription at Wilkinson's Pharmacy at 2.20pm on Thursday allegedly trying to get more medication than had been prescribed to her.
''The prescription had been written out by a doctor but had been altered ... trying to get more medication.''
He said pharmacy staff quickly picked up on the alteration.
It was possible she is a New Zealand or Australian holidaymaker.
Inquiries are continuing including in relation to the name on the prescription. Police have accessed CCTV footage of the woman.