The intra
{Latin - within} venous
{vein} route of administration is the fastest way to get drugs into your body and to feel the effects by injection. It is the most potent out of the following "common routes" - it allows the drug to act almost immediately, and can reach a high
plasma concentration efficiently. Large volumes of drug or even just fluid can be given this way.
Right into the bloodstream.
Unless you consider intrathecally - in the spinal cord. But that's another ball game.
Other common routes of injection (aka parenteral) drug administration are:
SC Subcutaneous and SM submucosal - under the skin and mucosa
IM Intramuscular - in the muscle
Some of the disadvantages of the IV route are:
Skill is required to insert the needle into a vein - a haematoma may be produced if the vein wall of torn.
Infection may be carried into the bloostream - a major hazard for IVDUs (intravenous drug users) aka drug addicts
The sudden entry of the drug into the blood can cause toxic or particularly severe allergic reaction.
Some drugs or their solvents are irritant to vessel walls and can cause thrombophlebitis - e.g. propylene glycol solvent for diazepam.