Hi Delta,
First

. It's scary to find out stuff that we consider to be so far left field they are not on our radar. Especially things that are often painted in the light of "Daggers and Cloaks".
I'm going to write my post as someone who worked in the field of Alcohol and Other Drugs for 4.5 years.
The first thing you need to do is decide how involved you want to be with this. You also need to talk with your sister to find out what, when, how, why, where, how frequently she takes drugs. Be prepared for her to tell you to sod off. You need to make it clear that you will not judge her. If you do judge her, you risk her closing up and not letting you in at all.
Lulu makes a good point. There are plenty of people in society who use drugs (including alcohol) recreationally (and some not so recreationally) who are able to hold down jobs and contribute to society in a positive manner. However, this does NOT mean that their drug use is not an issue.
You need to find out if your sister believes she has a problem. If she doesn't, then it doesn't matter what kind of threats, promises, pleas, or bargains you make - she is not going to change her behavior. She will simply find ways to hide it. If she does believe she has a problem, then you need to find out what she wants to do. She may want to abstain completely or she may want to abstain from only a couple of her substances. Or she may want to simply cut down on her usage. This is perfectly acceptable - she needs to start somewhere.
If your sister tells you that she doesn't want to change anything about her behaviour, then try to discuss
Harm Minimization with her. Depending on the substances she consumes and the route in which she consumes them, the advice would differ. However, the crux of the message is;
- Always use new unused needles for injecting. NEVER share injecting equipment.
- Always use SAFELY - in a group setting and preferably with one person "sober". Try to make sure one of those people knows CPR.
- If she is going out on the town, make sure someone she is with knows what she has taken and what quantities in case she collapses.
- Make sure she knows the gear she is using is GOOD QUALITY.
- If she is partying, stay hydrated with water especially if she is dancing or going to a rave.
- If someone she is with overdoses - call an ambulance immediately. Same applies for her. Many people are afraid to do this because they fear they will get into trouble.
Google Drug and Alcohol services in your area. There should be a 24hr counselling and referral telephone service that can give you a list of numbers of services local to you. Be prepared to be put on a waiting list. This is a grossly underfunded area. I'm sorry I don't have the phone number for the counselling and referral line in your State.
If your sister does decide to abstain or go through withdrawal, or to let you in on her world, you will need supports for yourself. This could be through impartial friends, people on BB, or family. However, I strongly recommend professional support for yourself - you should be able to access this through any counselling service associated with drugs and alcohol. If you google Family Drug Help in Victoria, there is a website that may be of some assistance to you.
If your sister does decide that she wants to get off her substance/s of choice altogether, keep in mind that there are two parts to any addiction. The physcial need and the mental need. Physcial withdrawal can be very taxing on the body but it usually fairly short. The mental dependance on the substance is much more difficult to treat and manage. It will require a change in her way of thinking, habits, and possibly even her circle of friends and associates.
There are many people who have come off drugs on their own. However, I strongly recommend professional help. A drug and alcohol counsellor (they often come from varying backgrounds and can be nurses, psychologists, social workers, counsellors), a good GP. There are private and public avenues - don't be fooled into thinking that private is necessarily better but they will have shorter waiting lists.
Good luck.
MG