He drew on a report by the Global Commission on Drug Policy which, two months ago, said the international War on Drugs was a failure and recommended governments explore legalising marijuana and other controlled substances, he said.
"They reported that drug prohibition has had devastating effects on individuals and societies all around the world and said the War on Drugs as we know it should end."
In a brief statement today a spokeswoman for Prime Minister John Key said: "National has long held the view this would be a step in the wrong direction".
Police Minister Judith Collins said ACT's cannabis policy was going in the wrong direction.
Family First national director Bob McCoskrie said Dr Brash's calls to decriminalise marijuana was dangerous.
"A weak-kneed approach to marijuana use will simply send all the wrong messages that small amounts of drug use or dealing aren't that big a deal."
ACT should be calling for better treatment facilities for addiction, he said.
"A zero-tolerance approach to the use of drugs combined with treatment options is a far better solution."
In Dr Brash's speech he also said a fundamental right was the right to defend oneself from attack.
"Everyone is justified in using, in defence of himself or another, such force as, in the circumstances as he believes them to be, it is reasonable to use."
"I believe that the right to self-defence should be enshrined in our Bill of Rights also."
He said ACT was still in the process of formulating its law and order policy, but when the party did announce it there would be four over-arching themes.
They are:
* Making sure the government does as much as possible to keep you safe from criminals.
* Making sure that when the government can't be there, you won't be criminalised for taking reasonable steps to keep yourself safe from criminals.
* Making sure you're not criminalised for any action that is in fact a victimless crime; and
* Making sure victims are not treated as criminals, and criminals are not treated as victims.
