A 49-year-old Hamilton Hill woman has been charged with two counts of offering to supply cannabis and two counts of conspiracy to possess heroin.

Another 49-year-old woman of Hamilton Hill has been charged with 30 counts of offering to supply heroin, one count of possession of heroin and one count of supplying the drug.

A 67-year-old East Perth woman has been charged with 12 counts of offering to supply heroin and one count of possessing heroin.

The four women were released on bail and are expected to appear in the Perth Magistrates Court on March 27.

The WASUA's website states it is the organisation's mission to improve the health and social circumstances of substance users, utilising a framework underpinned by harm reduction and peer education.