Most drugs are detectable in urine for one to three days after their use. It is difficult to predict whether a urine test will be positive for drug use, as this can vary a lot between people and depends on a number of factors including the amount of drug taken, the rate of metabolism for that drug, the length of time the urine has been in the bladder, and the amount of water consumed. Some drugs are detectable over longer periods of time, such as benzodiazepines (diazepam, temazepam, oxazepam etc.), which can be detected up to a week later, and cannabis, which can be detected up to a month later. Drinking large amounts of water can dilute the urine sample, making it less likely that any drugs will be detected; however, most laboratories also test how diluted the urine sample is.

Since very many factors can affect how long a drug is detectable in urine, the following figures (based on information from the Department of Corrective Services (1997) Operations Procedures Manual) are only a rough guide. Testing is becoming progressively more sophisticated and accurate.

Hair samples can contain traces of drugs if the drugs were used when the hair was being formed in the scalp or if drugs come into contact with the hair externally. Hair grows at the rate of approximately one centimetre per month and dividing the hair into one centimetre fragments can be used to plot the pattern of drug use over an extended period.

Sweat can also be used to detect drug use with sweat patches (like patches for giving up smoking), although commercial testing for sweat is not yet routinely available in Victoria.

Commercial tests exist for on-the-spot testing of saliva. The detection times for drugs in saliva are similar to detection times for drugs in urine.