Drugs can stay in the body for different lengths of time.  The length of time that drugs stay in your body will depend on your size, metabolism, and the amount of drugs that are used.   

As for alcohol, it takes a few days to eliminate it from your body.  It can take women a bit longer than men before the alcohol is out of the system.  A drug test can detect alcohol in your system for 12 - 24 hours after drinking.   

Amphetamines will be passed from the body in a few days.  A urine test can reveal the use of amphetamines for between 1 - 4 days after it is used.   

Short acting barbiturates will remain in the body for up to five days while the long acting barbiturates can stay in the body for 24 days or longer, depending on the amount used and length of time that it is used.  Barbiturates can be detected in the urine for up to 21 days after it is used. 

Benzodiazepines may be eliminated from the body in a few days, a week or it could take quite a bit longer.  The use of benzodiazepines can be detected by a urine test for up to 42 days after it is taken. 

Cannabis is fat-soluble and its metabolites will lodge in fat cells.  Single marijuana use can be detected by a urine test for up to three days or more while a blood test will reveal its use for two to three days afterwards.  It will show up in a saliva test for up to 24 hours afterwards.  Habitual marijuana use will be revealed for up to 12 weeks in a urine test while the blood test and saliva test results will be similar for single marijuana use.  A hair test can detect marijuana use for up to 90 days. 

While cocaine itself may pass out of the body in a few days, the resulting metabolites from use of cocaine are used to detect cocaine use.  These cocaine metabolites can persist in the body for up to 30 days after using cocaine.   

Depending on your use of opiates such as codeine, morphine, and heroin, the drug could be in your body for between one and forty days.  It depends on the amount that is used and the frequency of use.  These drugs can be detected by a hair test for up to 90 days after using, for between 2 - 5 days with urine test, codeine, and morphine can be detected for between 12 - 36 hours by a saliva test. 

Methamphetamines will stay in the body for between 2 - 4 days or much longer depending on the amount and frequency of use.  Methamphetamine use can be detected by a hair test for up to 90 days, by a urine test for 3 - 5 days and by a blood test for between 1- 3 days after using.   

PCP will stay in your body for between a few hours and up to two weeks, depending on the amount and frequency of use.  PCP can be detected by a hair test for up to 90 days, by a urine test for 3 - 7 days,  for 3 days by a saliva test and for between 1 - 3 days by a blood test.