The drug laws you should be particularly aware of are:
“Simple” Possession of Drugs
Simple possession of drugs can mean you actually possess the drug in a small enough amount to imply personal use.
Possession laws also apply when you don't actually have literal possession of the drug, but you have control over what happens to the drug, for example, you have the key to a locker which contains the drug, or if you have drugs stored in your car.
“Trafficking” of Drugs
Trafficking of drugs generally refers to the distribution or selling of drugs, commonly known as drug dealing. It also includes the growing or manufacturing of drugs, for example, growing cannabis or making methamphetamine. Trafficking also includes possession with intent to supply, which generally applies when you possess larger amounts of drugs than would be expected for personal use.
Importing and exporting of drugs are also a form of trafficking, so if you take drugs on holiday with you, it would be trafficking, not simple possession, even if it was for your own personal use.
The amount of a drug you possess is important -– if you possess a large amount of the drug, it can be understood that there is an intent for you to supply the drug to other people. This is much more serious than if you possess a small amount of a drug, which appears to be for personal use.
You should bear this in mind – you may be tempted to purchase a larger amount of a drug for personal use, in order to save money or to share with friends. If you are found with a larger amount in your possession, you may be seen as possessing with intent to supply, even if it is really for your own use. If you intend to share it with friends, the situation gets worse, as it is not for personal use.
Possession of Drug-Related Items
There are also laws prohibiting substances which can be used to cultivate or manufacture drugs, and paraphernalia which is used to consume drugs, such as crack pipes and syringes.
Where You Are When Possessing Drugs
The laws also take into consideration where you have possession of drugs, and in particular, whether you are at or near somewhere where there are vulnerable people, such as a school or daycare. The seriousness of the possession charges increase in places like this.Source
US Drug Enforcement Administration. The Controlled Substances Act http://www.usdoj.gov/dea/pubs/abuse/1-csa.htm Accessed Feb 20 2009.
US Legal. Drug Offenses Law and Legal Definition. http://definitions.uslegal.com/d/drug-offenses/ Accessed Feb 20 2009.
US Legal. Drug Possession Law and Legal Definition. http://definitions.uslegal.com/d/drug-possession/ Accessed Feb 20 2009.