Eating or drinking a drug is probably the simplest and oldest method of taking it. The drug is absorbed through the lining of the stomach and small intestine - see animation - and enters the bloodstream. Its next port of call is the liver where some of the drug will be eliminated from the blood before it is passed on to the heart.

The heart, which is just a pump, pushes the blood into and around the lungs where it is oxygenated before it is returned to the other side of the heart. The newly oxygenated blood is finally pumped up to the brain and central nervous system where the drugs begin to have an effect.

The slowest method.

The digestive system route is the slowest method of getting drugs to the brain. It is dependent on how full the stomach and small intestines are and what else they contain. This affects the rate of absorption at the time of ingestion.

The effects of the drug, using this method, may not be felt for between 20 and 45 minutes. Dose is therefore difficult to control as is classically the case with drinking alcohol or eating cannabis. The problem is that by the time that the user begins to get feelings of intoxication, there is a backlog of upto 30 minutes worth of alcohol or drugs still waiting to get to the central nervous system. Even if the user stops drinking or eating the drug immediately they feel an effect, they can end up having taken too much.

The risks.

The long-term risks of using drugs in this way can include damage to the stomach, intestines, liver and kidneys. The liver is particularly at risk and can suffer progressive and irreversible damage from excessive use of drugs and alcohol.