Carl Olsen, head of Iowa NORML, called the measure "incredibly harsh" and cautioned that the new law could entangle many casual marijuana users in the criminal justice system. "People who now face a maximum six month jail term in Iowa for the simple possession of small amounts of marijuana will face two years in prison and a $5,000 fine for third and subsequent offenses," he said.

Senate Bill 2391 also allows law enforcement to check motorists for the presence of marijuana metabolites—presumably by urine or blood tests -- if there is a reasonable suspicion to believe the motorist is driving under the influence of the drug. Because the law sets no legal threshold for drugs other than alcohol, S.B. 2391 states that the detection of any amount of marijuana metabolites is grounds for obtaining a conviction of driving while intoxicated. The law fails to specify how or where police will administer the drug tests.

"The presence of non-psychoactive marijuana metabolites in the urine is not evidence of impairment," warned Allen St. Pierre, Executive Director of The NORML Foundation. St. Pierre noted that metabolites often remain in the urine for days and sometimes weeks after the intoxicating effects of marijuana have worn off. "You could have someone who smoked marijuana on Sunday be arrested on Tuesday and charged with driving under the influence," he said.

Attorney Tanya Kangas, Director of Litigation for The NORML Foundation, questioned the constitutionality of the drug-testing proposal. "Implementing S.B. 2391 will violate privacy and search protections," she said. "Blood tests are excessively invasive; urine tests do not indicate impairment and cannot be collected consistent with constitutional standards for traffic stop searches. We can restrict people from driving while impaired without violating the Constitution as this law proposes."