To my knowledge, there are a number of people in prison for possessing/using marijuana. There was a recent Pew poll that said more Americans support legalization now more than ever.

If I were imprisoned for some period of time (say three months) and, during those three months, the law no longer dictated the same punishment (say a fine or mandated rehab etc. instead) would I still face the same prison sentence?

Marijuana use is just an example, I'm wondering if there would be overarching effects in all laws in this way. (Keeping with imprisonment, because of it's on-going nature, rather than a fine or something)

"Ex post facto" is a phrase that seems like there might be some relationship, but I'm not too brushed up on my political Latin, or sentencing decisions to know if there is a precedence in place for something like this.

  • I don't know about those that are presently incarcerated, but when Washington State recently legalized it, they dropped charges for those that were pending: thinkprogress.org/justice/2012/11/10/1176151/…
    – user1530
    Apr 21, 2013 at 2:30
  • I would expect that the answer might be found in what exactly happened once Prohibition was repealed.
    – user4012
    Apr 21, 2013 at 17:46
  • no but the law usually has a provision freeing any & all from the old law...even that has exceptions...
    – user1726
    May 6, 2013 at 2:38
  • @user1530 In the case where your case is still pending, and it gets legalized in the meantime, avoiding conviction is as easy as getting a jury trial. (Though, in America) The pending cases were probably dropped to save everyone's time mostly.
    – bobsburner
    Feb 18, 2020 at 16:22

1 Answer 1



An ex post facto law is one that acts retroactively, whether positively or negatively (completely dependent on your point of view). The US Constitution explicitly prohibits them:

No Bill of Attainder or ex post facto Law shall be passed

However, according to Calder v. Bull - 3 U.S. 386 (1798), the definition is slightly narrower than this:

1st. Every law that makes an action done before the passing of the law and which was innocent when done, criminal and punishes such action. 2nd. Every law that aggravates a crime, or makes it greater than it was when committed. 3rd. Every law that changes the punishment, and inflicts a greater punishment than the law annexed to the crime, when committed. 4th. Every law that alters the legal rules of evidence and receives less or different testimony than the law required at the time of the commission of the offense in order to convict the offender

That is to say that you cannot negatively affect a person with a law that retrospectively changes the situation at the time of the offence. This implicitly states that the decriminalisation of an act or lessening of a punishment can be retrospectively applied.

In Hoyt Weaver v. Robert Graham, Governor of Florida. 450 U.S. 24, 101 S.Ct. 960 Justice Marshall referencing Cader v. Bull (among others), decided (my emphasis):

Regardless of whether or not the prospect of gain time was in some technical sense part of the petitioner's sentence, the statute substantially alters the consequences attached to a crime already completed, changing the quantum of punishment, and thus is a retrospective law which can be constitutionally applied to petitioner only if it is not to his detriment

An example of a reduction in sentencing is, S. 1789 (111th): Fair Sentencing Act of 2010, which was enacted after a number of attempts by both houses. This amended a number of previous acts to reduce the disparity in sentencing for those found in possession of crack cocaine as opposed to powder cocaine. This did not reduce the sentence of those already imprisoned under the amended acts.

The crucial point is that any act, which reduced the sentencing for, say, possession of marijuana would have to explicitly state that it is being applied retroactively in order to automatically release people from prison (a physical and administrative act that, itself, may take a while). An act could also offer guidance to parole boards that releasing a prisoner is the preferred method, allowing the release of prisoners to gradually filter through. I can't find any examples of this actually happening in the US, though I'm sure it has.

Europe has an, almost identical, definition. The European Convention on Human Rights (ECHR), in Article 7 states:

  1. No one shall be held guilty of any criminal offence on account of any act or omission which did not constitute a criminal offence under national or international law at the time when it was committed. Nor shall a heavier penalty be imposed than the one that was applicable at the time the criminal offence was committed.
  2. This article shall not prejudice the trial and punishment of any person for any act or omission which, at the time when it was committed, was criminal according to the general principles of law recognised by civilised nations.

Don't forget that the ECHR applies to all members of the Council of Europe, not just the EU. Though, the Treaty of Lisbon contained a protocol allowing for the accession of the EU to the Council:

arrangements for the Union's possible participation in the control bodies of the European Convention;

One of the more notable, retrospective, criminal Acts in the UK is the War Crimes Act 1991, which allowed for the punishment, by British Courts, of people responsible for war crimes during WWII, i.e. before the Geneva Conventions. This would, theoretically, have been in breach of the ECHR.

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