4.9g is bullshit, that's more like about 15 or 16 pills weight, anyways the way they do it over here (WA) is they bust you on the actual weight of the drug they're busting you for, say the pills are 50% mdma and they weigh 1.5g then they'll bust you fot 0.75g mdma, which is fuck all, maybe a fine and a CSO or at worst and ISO and a curfew.
This is definitely not the case and it has been this way since
Fursman (as tiggz has said) which is a late 1980's decision (from memory).
If you were charged under Commonwealth law then they do consider the pure amount. But I doubt you were charged under their laws because that would necessarily mean you were involved in importation.
It is an unfair system to a degree, especially with ecstasy pills, as the weight goes up very quickly. Most MDMA tablets weigh between 200 to 350mg. Purity can range from 20 to 50%. With MDMA, one pill means one dose or hit (so ~10 hits per 3 grams). 3 grams of high purity methylamphetamine could of course be as many as 150 street "hits". The inequality is obvious. So whatever the total mass of the substance is, is the quantity of drugs possessed. Purity becomes relevant to sentence.
I think we can all agree that that's pretty unfair though! I mean, what if you dropped your point of meth into a kilo of baking soda? All of a sudden do you have a kilo of meth? Drug lord!!!!!!
If you mean dropped accidentally then one could never know they possessed methylamphetamine when they possessed the baking soda. Read
Paul v Collins again, focusing on what was said regarding the element of knowledge in
Williams and
He Kaw Teh. It would be an absurdity if quantities of drugs are accidentally introduced into other powders, and it be alleged that the hapless possessor of the innocuous powder should somehow be in possession of a shitload of drugs. Having regard to the caselaw above, the law would not treat this situation this stupidly. (The police might, but they are not the law. They only attempt to enforce what they view is the law, and are often found wanting in that regard.)
Possession with intent and presumptive amounts
The quantities stated under a relevant state's laws are not necessarily the end of the matter.
In WA, as tiggz has said, the presumptive amount for intent to sell or supply is 2 grams. That is, you are presumed to possess the drugs with that intent if you possess more than 2 grams.
But the prosecution must still prove you had an intent to sell or supply beyond reasonable doubt. The onus of proof is not strictly reversed, although it can often seem that way. Clearly, the greater quantity one has, the more easily an intent could be proved. But often it will be other evidence that goes to show one is possessing with an intent to sell/supply. Multiple bags of the same pill is one, admissions about giving some to friends or holding them for the real owner is a slam dunk for the prosecution.
You can also be charged with possession with intent despite having less than 2 grams. If you possessed 1 gram of meth, split in 10 separate deal bags for a point each, you would be stuffed. It is a clear case of possession with intent to sell to others, because of the manner in which you have divided it, irrespective that it was less than the 2 grams.
As tiggz says, evidence that goes to show you possessed only for personal use could be led by you to rebut the presumption, or in keeping with the prosecution onus of proof, weakening the inference that you possessed with an intent to sell or supply, such that it cannot be said beyond reasonable doubt you had that intent.
Sentencing
Sentencing is extremely subjective and no hard or fast rules should be assumed. This is the case Australia wide. What could be a fine for one person may be a community order for another or even worse for someone else. In WA most cases of drug possession result in a fine.
Convictions for sell/supply could result in anything from an order to a prison sentence. Age, prior record, personal circumstances, whether it can be shown the operation had a significant commercial element and sadly the identity of the sentencing Judge/Magistrate are all factors. Drug traffickers (over 28grams in the case of MDMA, meth, heroin and cocaine) would almost inevitably be given a prison sentence, often quite a substantial one.
This is the case across Australia but every jurisdiction's laws vary widely, including the relevant amounts that one can possess before they are placed into different categories. That language is also very different. A traffickable quantity in WA may be a commercial quantity in NSW. Know your own state's drug laws and if you ever, ever get into trouble, say nothing and find a lawyer who knows your state's laws and sentencing practices inside out. You will not regret it