The changes, on their face, are simple. The blanket ban on the possession, use, storage and cultivation of cannabis has been lifted. In the ACT, cannabis is no longer an entirely prohibited substance. A user, however, is not allowed to smoke cannabis in a public place or near a child. The new laws do not decriminalise the selling and trafficking of cannabis. That remains illegal under both federal and territory law.

If you share your cannabis with friends in the seclusion of your private Canberra residence, have you broken the law? The answer is possibly. While laws regarding the manufacture, possession and supply of cannabis are largely the remit of the territory, the Commonwealth is responsible for upholding Australia's international obligations. This includes obligations under the convention against drug trafficking (which includes obligations in relation to the regulation, selling and trafficking of cannabis). Therefore, as a matter of federal law cannabis is a "controlled drug", and so it is illegal to possess, sell or commercially cultivate cannabis.

Does the federal law apply to you? The answer is absolutely. The question is the extent to which the ACT laws provide for a legal loophole.

The federal law exempts conduct that is excused or justified by territory law, which, if read plainly, would appear to excuse cannabis use in the ACT (to the extent it is "legalised" by the new territory legislation). However, legal specialists warn that it is not clear whether the new ACT laws actually decriminalise the use of cannabis. The federal Attorney-General, Christian Porter, has expressed the view that federal law will override the territory's law in governing the day-to-day actions of Canberrans, given how the new laws are phrased. By contrast, Professor Desmond Manderson of the ANU College of Law considers that it is a question for the courts to work out. Professor Manderson recently told the ABC that "there will have to be a court case to work out the meaning of the provisions in the Commonwealth Crimes Act that recognises the freedom of state and territory governments to make their own drug laws".

So, can the police arrest you for smoking or sharing cannabis in the ACT? At this stage, it's not clear.

The above has some relevance to the fact that I am often asked whether drug testing in the workplace is lawful. The short answer is yes, as long as it is justifiable - which it often is in professions like medicine or construction where a drug-affected employee may be a danger to those that they work around and the public. Employers have the right to expect that their employees are sober or otherwise not affected by mind-altering drugs. Being under the influence of any drug at work, legal or not, can, from at least the perspective of work health and safety, constitute employee misconduct and be cause for termination of employment (think alcohol or heavy pain medication).

Drug testing policies differ between workplaces. Some companies require their employees to submit to random drug tests. Drug testing (and especially random testing) is controversial for a number of reasons. First, it is an invasion of privacy, both in the conducting of the drug test - impromptu drug tests often require the employee to give a urine sample in the presence of a third party - and in the collecting of that employee's biometric data and medical information. Second, drug test results can be inaccurate and unhelpful in determining whether an employee is adversely under the influence of a drug at work. Test results will show whether traces of drugs are in a person's hair, saliva, nail or urine; they are less precise about when the person took the drug. Cannabis, for example, is metabolised at a slow rate and can be detected for up to 90 days after use, depending on the method of testing.

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The inaccuracies in test results can be used to an employee's advantage when disputing allegations of being under the influence of drugs at work. Unless the employer has concrete evidence of drug use on their property, it is unlikely that a positive drug test will, on the "balance of probabilities" - the level of burden of proof used in employment investigations - prove the exact time the person used drugs. However, if you find yourself in the middle of a workplace investigation on suspicion of being under the influence of cannabis at work, you are not in an enviable position. Should you be unsuccessful in convincing your employer that you were not incapacitated by the drug at work you will likely be facing termination of employment for misconduct, and for public sector workers (at least until the conflicting federal and territory laws are clarified) also for a possible breach of section 13(4) of the APS Code of Conduct (or its equivalent for ACT public servants under the Public Sector Management Act): "An APS employee, when acting in connection with APS employment, must comply with all applicable Australian laws."

If there is no question that your cannabis use was out of work hours, then, generally speaking, your out-of-hours conduct should not be relevant to your employment. There are a few exceptions to this - for example, if you work in a law-enforcement agency engaging in illegal activities may be considered to strike at the heart of your employment relationship and possibly cause damage to your employer's reputation and be grounds for dismissal.

In short, I would not recommend anybody enthusiastically embrace the decriminalisation of cannabis in the ACT until we receive confirmation from the courts of the effect of the new ACT laws - especially for employees of law-enforcement agencies.