I had someone recently ask me if they would get arrested in Iowa for possession of a small amount of marijuana. The most straightforward answer a criminal lawyer can give is yes. In Iowa, no amount of marijuana is legal to possess, not even for personal use, medical use, or to feed to your dog. No excuses, whatsoever.
Now, just like other jurisdictions, police officers in Iowa have discretion to make an arrest. If a particular officer in a particular situation doesn't want to arrest someone for a burned up blunt in the ashtray, fine, it's his call. But nine times out of ten, you are at least getting a criminal citation which will result in a prosecution for a serious misdemeanor. Most of the time though you're getting outright arrested and booked into jail.
Other jurisdictions are not so harsh. In various States possession of less than four grams or some other low amount is a non-arrestable offense, you may get a ticket like a speeding ticket, but you pay a small fine and you're done. That is not Iowa. I have seen people in Polk County get prosecuted for residue in a pipe. If there is enough "substance" to test, you can be prosecuted. Most of the time, even if that type of case is filed you will be able to work with the prosecutor to get a fair resolution. If not, those are cases that need to be taken to trial, where the decision to convict is up to the jury. Prosecutors that take on those types of cases to trial aren't going to have a high success rate. My experience is that small quantity pot cases are some of the toughest to win for the State. I'd say on any jury of 12 people at least 3 are occasional or moderate marijuana users. If the defense attorney can give them ANY reason to acquit their client they will be ready and willing to do so.
The outright jury nullification argument, however, is not likely to win any cases or gain you any respect from the Court. Besides being unethical, you will always have two or three people who think all drugs, even pot, are the scourge of the earth. They will vote to convict on almost any evidence of guilt. As a defense attorney, you have to give the pot smokers a little ammunition to fight these people. Most of the time your client will be in a situation where you can argue a lack of knowledge or attack "constructive possession": It wasn't my coat, someone else put it in my purse, I was just the passenger in the car etc. If you've got something to talk about, you're alive.
Given the increasing strain on courts and probation personnel, Iowa would do well to adopt this method of handling marijuana cases. They could put a $500.00 fine on possession and free up thousands of man hours and tax dollars by doing this instead of putting people on probation. Fewer court appointed attorneys and less judicial resources (judges, probation officers, court clerks) along with a higher fine would be a financial moneymaker for the State. Unfortunately, I just don't ever see the people that brought you the two-thousand foot law for sex offenders getting around to this issue anytime soon.
Bottom line is, in Iowa you take the risk of criminal prosecution for even the tiniest amount of marijuana. Be warned, beware.