Drug injection
Injection  of recreational drugs is a method of the drug into the body with a hollow needle and a syringe which is pierced through the skin into the body. 
Although there are various methods of taking drugs, injection is favoured by some users as the full effects of the drug are experienced very quickly, typically in five to ten seconds. This shorter, more intense high can lead to a dependency, both physical and psychological, developing more quickly than with other methods of taking drugs.
While a wide variety of drugs are injected, among the most popular in many countries are morphine, heroin, cocaine, amphetamine and methamphetamine. Other drugs that are injected less often include MDMA and certain prescription medications distributed in pill or capsule, or even suppository form such as benzodiazepines, meprobamate, and narcotics such as Palladone  or Dilaudid (hydromorphone), Numorphan (oxymorphone), OxyContin, OxyNorm, Eukodol, Proladone, and others oxycodone, Morzet or Vilan (nicomorphine), Palfium (dextromoramide), Symoron methadone, dipipanone, and MS Contin and many other morphine formulations.  Injecting codeine into the bloodstream directly is dangerous because it can cause pulmonary oedema and anaphylaxis, and dihydrocodeine, hydrocodone, nicocodeine, thebacon and other codeine-based products are also moderate risk in this case.
Some manufacturers add narcotic antagonists to pills to prevent this, including Talwin NX pentazocine, Heptadon (laevomethadone a.k.a. d, l-methadone and levomethadone), Valoron (tilidine), and Lomotil (diphenoxylate) contains subtherapeutic doses of atropine (about 2,5% of the therapeutic dose for GI problems and mild organophosphate poisoning;  formerly a formulation of morphine in the USA also contained atropine for the same reason.  Unlike the naloxone in the other formulations listed above, atropine does indeed help morphine and other narcotics combat neuralgic pain.  The atropine may very well not present a problem, and there is the possibility for soluble tablets having their atropine content reduced by putting them on an ink blotter and putting a drop of water on them and taking the remainder of the pill off the blotter and cooking it up.  Canada and many other countries prohibit manufacturers from putting in active ingredients for the above given reason; their Talwin PX does not contain naloxone -- being a narcotic agonist-antagonist though, pentazocine and its relatives can cause withdrawal in those physically dependent upon narcotics.
Of all the ways to get drugs into the system, injection has the most risks by far as it bypasses the body's natural filtering mechanisms against viruses, bacteria and foreign objects. There will always be much less risk of overdose, infections and health problems with alternatives to injecting, such as smoking, snorting (nasal ingestion), or swallowing.
Viruses such as HIV and hepatitis C are prevalent among injecting drug users in many countries, mostly due to small groups possibly sharing injection equipment combined with a lack of proper sterilization. Other health problems arise from poor hygiene and injection technique (be it IV, IM, or SC), such as Cotton Fever, also known as the Shakes, phlebitis, abscesses, vein collapse, ulcers, malaria, gas gangrene, tetanus, septicaemia, thrombosis and embolism and the results thereof, lodging of pill fragments in small blood vessels, the lungs, and elsewhere, and local infections.  Hitting arteries and nerves is dangerous, painful, and presents its own similar spectrum of problems.

# Harm reduction
Harm reduction is a philosophy of public health intended to be a progressive alternative to the prohibition of certain lifestyle choices such as the taking of illicit drugs. While it does not condone the taking of illicit drugs, it does seek to reduce the harms arising from their use, both for the person taking illicit drugs and the wider community.

# Safer injection of illicit drugs
A philosophy of harm reduction promotes information and resources for injecting drug users. General guidelines on safer injecting various substances intravenously are typically based on the following steps.
The preparation area for drug preparation should be cleaned with warm soapy water to minimize the risk of bacterial infection.
The equipment required involves new syringes and needles, swabs, sterile water, filter, tourniquet and a clean spoon or stericup. The person should soap their hands with warm water and use a swab to wipe down the spoon. The swab should be wiped once, in one direction only, over the injection site and another swab used on the spoon.
A person should not inject alone a dose from an unknown batch due to the dangers of overdosing. They also should under no circumstances share any of their injecting equipment, even tourniquets, due to the high danger of bacterial and viral transmission.
Sterile water should be drawn into the syringe with the needle uncapped to prevent blunting, then into the spoon to prepare the mix. Where sterile water is not obtainable, the next option is tap water boiled for five minutes.
Some drugs need heat applied to mix with the water completely, especially when relatively little water must dissolve relatively much of a drug. The mix should be allowed to cool to preferably less than 110 F (43 C) before injecting. Heroin in its base form (brown Afghan heroin, the most common form in Europe) require an acid to render the mix pH neutral. While some people use lemon juice to do this, this can lead to serious bacterial and/or fungal infections. Citric acid or ascorbic acid (Vitamin C) is the best option and is usually available in supermarkets in granular form. The next best option is vinegar which will have less chance of bacteria than lemon juice but will be easy to cause burns because it is hard to dose.
Drugs which come as pills (such as Oxycodone and Benzodiazepine) with lots of waxy binders, carnauba wax in particular, can be dissolved by using an alcohol swab stripping any coatings off the pill and then leaving the tablet to dissolve in water for 5-15 minutes.
Suppositories can be injected by melting them in a little hot water and then letting the resultant liquid cool int he refrigerator for a number of hours, after which the liquid on top is drawn off with a pipette, syringe, or eye dropper
The mix should be drawn up into the syringe through a filter. The ideal here is a wheel filter, preferably 0,2 micrometres, which will filter all microorganisms, but not viruses. Ground up prescription pills usually contain many fillers that can lead to very serious health problems if injected, including lung embolies that may be trivial but also life threatening. Although not as efficient, alternative filters include cotton wool, tampons or cigarette filters (if they do not have a fibreglass base).
Once the mix is drawn into the syringe, remove any air bubbles by flicking the barrel with the needle pointed upwards. At the same time, gently push the plunger to expel any air.
Place a tourniquet above the injection site (injection sites should be rotated to allow veins to heal). The tourniquet should not be on too tight, or left on for too long. With the bevel (the needles 'hole') facing upward, the needle should be eased into the vein at a 45 degree angle. Make sure the needle is going in the same direction as the blood flow.
The plunger should be pulled back a little (jacked back) to see if the needle is in the vein. Blood should appear in the barrel of the syringe if this is the case. This process is known as registering.
Take the tourniquet (or, 'tie') off and gently press the plunger; although it is a good idea to re-register the vein after removing the tie and before you finish the dose, just in case. If it hurts or there is pressure against the plunger, stop immediately as the vein has probably been missed. After injection, remove the syringe and keep a clean tissue or cotton wool against the injection site to prevent bleeding. Dont use a swab to do this as the alcohol base prevents the blood from clotting.
Dispose of injecting gear using a 'sharps bin' if supplied. Otherwise place the used equipment in a rigid-walled container such as a bottle and dispose of safely.

# Alternatives to injection
The safest alternative is, of course, not to take illicit drugs. The majority of legal systems around the world encourage this option. Harm reduction acknowledges that some people in a society will not choose this option and will at least provide information to safer means of taking illicit drugs to minimise the individual health risks, and also the spread of viruses such as HIV and hepatitis C to the wider community.
Snorting, or nasal ingestion of drugs, is usually safer than injection in terms of the relative danger of transmission of blood-borne viruses. However, the membranes in the nose are very delicate and can rupture when snorting so users should have their own snorting equipment not shared with anyone else, to prevent viral transmission. As with injection, a clean preparation surface is required to prepare a drug for snorting. Nasal membranes can be seriously damaged from regular snorting.
Smoking, often called 'chasing the dragon', has negligible risk of bacterial or viral transmission and the risk of overdose is lessened compared to injecting. It still retains much of the 'rush' of injecting as the effects of the drug occur very rapidly. It is a far safer way to use heroin, with the best option being to use new aluminium foil, first passing a cigarette lighter flame over both sides to get rid of any contaminants.
Swallowing tends to the safest and slowest method of ingesting drugs. It is safer as the body has a much greater chance to filter out impurities. As the drug comes on slower, the effect tends to last longer as well, making it a favourite technique on the dance scene for speed and ecstasy. People rarely take heroin orally, as it is converted to morphine in the stomach and its strength is halved in the process. Pills like benzodiazepines are best swallowed as they have chalk or wax fillers in them. These fillers wont irritate the stomach, but pose serious health risk for veins or nasal membranes.
Shafting, or rectal ingestion, relies on the many veins in the anal passage passing the drug into the blood stream quite rapidly. Some users find that trading off some of the 'rush' for fewer health risks is a good compromise. Shafting usually involves about 1.5 ml of fluid mixed with the drug. While squatting, gently insert the syringe (without the needle) until it is just inside the anus then ease the plunger down. A bit of Vaseline or lubricant will help if there is any pain. The sphincter muscles should be strong enough to hold the mix inside while it is absorbed. It can pay to do a trial run with water first.
Women have the added option of shelving, where drugs can be inserted in the vagina. This is similar to the rectum, in that there are many blood vessels behind a very thin wall of cells, so the drug passes into the blood stream very quickly. Care should be taken with drugs such as amphetamine that may irritate the sensitive lining of the rectum and vagina.