Are saliva drug tests very accurate?

'''The primary advantages of saliva drug testing could be described as: - ''' 1) A relatively non-invasive technique with specimen collection that can be observed without embarrassment to the person under investigation. 2) Little chance of sample adulteration since the whole sample collection procedure can be supervised. 3) Commercial screening devices are available for saliva monitoring that have been evaluated by some police forces for roadside drug screening use. The disadvantages of saliva drug testing are: - 1) Small specimen volumes restricting the number of analyses that can be performed 2) Contamination of the mouth may affect drugs screening results 3) Adulteration feasible due to oral contamination 4) Difficult to collect from those abusing stimulants such as amphetamines and ecstasy 5) Routine screening procedures not always applicable to screening saliva 6) Low concentrations make detection difficult and necessitate the use of expensive equipment