An anti-drugs lobby group has told the Legislative Assembly that medical marijuana could act as a "Trojan horse" for illegal drug use in the ACT and any change to current laws could prompt an increase in addiction.

Drug Free Australia representatives Gary Christian and Ross Colquhoun are scheduled to give evidence on Tuesday to a public hearing considering a medical cannabis scheme proposed by Greens Minister Shane Rattenbury.

Cannabis plants: Drug Free Australia has outlined seven primary objections to medical cannabis use in the ACT.

The lobby group's 125-page submission to the inquiry outlines domestic and international evidence that is critical of medical cannabis schemes and says reform is not needed in Australia because some patients already have access to legal synthetic cannabinoid drugs.

Drug Free Australia is affiliated with conservative organisations including the Australian Family Association and Melbourne-based Christian ethics group Salt Shakers. Political campaign group the Australian Christian Lobby has linked to its materials online.