body Alcohol Alcohol enters your central nervous system through the blood stream through the lining within your stomach and your small intestine. Once it is in your blood stream, is passes through your blood brain barrier via blood circulation. The alcohol absorbed will reduce your reflexes, interfere with nerve impulses, prolong muscle responses, and affect other parts of your body as well. Marijuana Marijuana, like alcohol, is also absorbed into the blood stream and passed through the blood brain barrier. However, the THC that is released from marijuana attaches to the CB-1 cannabinoid receptors which causes all of the effects experienced. These effects include, but are not limited to, mood changes, altered perception of time, and increased sensitivity. Cocaine Cocaine is a stimulant unlike Marijuana or Alcohol. As soon as cocaine enters the bloodstream it reaches the brain in minutes. Dopamine levels are increased intensely and the effects can last up to about 30 minutes. The most common way to use cocaine is by snorting it through the nose but other methods could be by smoking it in a crystal rock form. But because dopamine levels are increased at such a rate this leads to an even worse come down leading to needing a higher dose to get the same effect as the time before if taken again. This is how some addictions begin. Some effects when taken are an increase of energy and happiness, paranoia, rapid heart rate, anxiety, etc... Examples Urine A urine sample is urine that has come from the bladder and can be provided or taken post-mortem. Urine is less likely to be infected with viruses such as HIV or Hepatitis B than blood samples. Many drugs have a higher concentration and can remain for much longer in urine than blood. Collection of urine samples can be taken in a non-invasive way which does not require professionals for collection. Urine is used for qualitative analysis as it cannot give any indication of impairment due to the fact that drug presence in urine only indicates prior exposure. Different drugs can also stay in your urine for different amounts of time. For example, alcohol will stay within your urine for 7–12 hours, cocaine metabolites will stay for 2–4 days, and morphine will stay for 48–74 hours. One drug that will stay in your urine for a varying amount of time (dependent on the usage and frequency) is marijuana.