The drugs were found during a search of a house in the town centre on Thursday at around 1pm.
Two men aged 21 and 44 and a teenage boy aged 17 years were detained in connection with the raid.
All three were subsequently released on police bail pending further enquiries.
The 21-year-old was charged with assault on police.
He is expected to appear before Downpatrick Magistrates' Court later this month.