Possession of a Dangerous Drug
To prove that a person ‘possessed’ a dangerous drug the prosecution must prove:
a) the substance was (or contained) a dangerous drug;
b) the person knew the substance was present; and
c) the person was able, if they chose, to exercise physical control of the substance.
These concepts of knowledge and control are essential to understanding the legal idea of possession.
The law recognises both physical possession (e.g. holding the drugs) and constructive possession (e.g. controlling premises in which drugs are stored). You can therefore be in possession of something that is in a place a long way away from you.
“Possession” is not at all the same idea as “ownership”. The court is not concerned with whether the drugs were “yours” or belonged to someone else. You can be in possession of something that you do not own; for example, if you are minding drugs to give back to another person.
If you hold drugs for someone else, even for moment, then you are in possession of them.
Where drugs are found in a place occupied by a person, then the starting point is that occupier is deemed to be in possession of the drugs. To avoid conviction the occupier must usually show that they did not know the drugs were there, and had no reason to suspect that they were there.
However, the rule about occupiers does not apply when the drugs are physically in the possession of another person. The occupier is also not usually responsible for drugs found in private areas within a shared property, even within a shared room. Suppose, for example, Jane and Michael share a house and drugs are found in Michael’s car in the garage. Jane would not be deemed to be in possession. However, if Michael had left drugs in their shared lounge room, Jane would be deemed to be in possession of those.
Very Small Amounts
To secure a conviction for possession, the prosecutor will usually have to prove that there was more than a trace amount of the drug. That is, there must usually be a measureable quantity of the drug.
In R v Stevenson the accused had a tiny amount of powder carefully wrapped and concealed in her handbag. The powder weighed 0.054 grams and contained a mere 0.009 grams of heroin. She was convicted.
That result can be contrasted with the case of Donnelly v Rose. In that case the police found 0.026 grams of powder wrapped in foil. An analysis showed the presence of heroin but the analyst was unable to measure the amount of heroin. Mr Rose’s conviction was quashed. The Court of Appeal held that the prosecution had to establish something more than the mere presence of a drug.
Donnelly v Rose was followed in Loweke v QPS, which was an appeal heard in the District Court. In that case 200mg of liquid was found in a syringe. The court found as a fact that the liquid had been set aside to be used in the future. There was methylamphetamine in the liquid, but the analysis did not say how much. It was held that the prosecution had to prove that there was more than a mere trace and must therefore prove a measurable amount. Mr Loweke was acquitted.
It should be noted that the decision in Donnelly v Rose has been criticised in decisions outside Queensland. In a case where the prosecution have evidence (such as an admission to the police) that the accused person knew of the presence of a drug then the general principles of possession should arguably apply. For now, Donnelly v Rose is binding on all Queensland courts below the Court of Appeal and Loweke is binding on the Magistrates Court.
It should also be noted that the prosecutor will not have to prove an amount if they can prove that the accused person intended the substance to have the same “pharmacological effect” as a dangerous drug. The term “pharmacological effect” is of uncertain scientific and legal meaning and is yet to be interpreted by the courts.
What is clear is that a trace amount, undetectable to the naked eye, is not enough to make a person guilty of a possession offence. People who return positive tests when scanned at airports or prison visits will not be prosecuted on the basis of the test result alone.
Mistake of Fact – “I thought the drugs were something else”
Ignorance of the law is never a defence. However, an honest and reasonable mistake is a defence. If the court accepted that you had an honest, reasonable but mistaken belief about whether some substance was a dangerous drug then you would be found not guilty. For example, suppose I am given a packet of itching powder as a birthday present, and it turns out to contain something illegal. If the Court accepts that I honestly and reasonably believed it was ordinary itching powder the court must find me not guilty.
However, at my trial, it would be for me to persuade the Court that I had made an honest and reasonable mistake. That is, I would have the burden of proving my mistaken state of mind, and that my mistake was reasonable in the circumstances. The standard of proof is the “balance of probabilities”, which means “more likely than not” or “better than 50%”.
 Dib v R (1991) 52 A Crim R 64
 Pelham v R (1995) 82 A Crim R 455
 R v Thomas (1981) 6 A Crim R 66; Todd v R (1982) 6 A Crim R 105
 Lawler v Prideaux  1 Qd R 186; 70 A Crim R 145
 Symes v Lawler  1 Qd R 226; 69 A Crim R 432
 R v Clare  QCA 558,  2 Qd R 619; Section 129(1)(d) Drugs Misuse Act 1986. It follows that in Queensland the “knowledge” element of possession is knowledge of the substance, and not knowledge that the substance is a dangerous drug. That is a point of difference between the laws of Queensland and other States, discussed in He Kaw Teh v The Queen  HCA 43, (1985) 157 CLR 523 and Tabe v R  HCA 59, (2005) 225 CLR 418