When Massachusetts police officers suspect that a driver is intoxicated by alcohol, they often ask the motorist to perform a standard field sobriety test. If the driver has trouble walking in a straight line or reciting the alphabet, the police officer may have a reasonable suspicion that the driver is drunk. A breath test or a blood test can also be used to measure the driver’s blood-alcohol content.

Because there is no good test for marijuana intoxication, police officers have a lot more difficulty proving that drivers are stoned. A Massachusetts public defender has asked the state’s Supreme Judicial Court to disallow the use of field sobriety tests as evidence for marijuana intoxication. According to the attorney, there is no proof that flunking a field sobriety test indicates marijuana intoxication.

If field sobriety tests cannot be relied upon for evidence, police officers must use other methods to test whether a driver is high on marijuana. However, due to the way that the body processes THC, blood tests are not reliable measures of marijuana intoxication either. A person who tests positive for THC in a blood test may have smoked pot one hour ago, three days ago or two weeks ago.

Now that recreational marijuana has been legalized in many states, police officers may be on the lookout for stoned drivers. People charged with impaired driving may be able to dispute their charges by arguing that prosecutors do not have reliable evidence. An attorney may be able to help an individual with this effort by proving that the testing methods that were used were unreliable measures of intoxication.