Source: Washington Marijuana Association, Facebook

The marijuana movement is transforming before our eyes, whether you're for legalization, against it, or are undecided.

Over the past two decades, nearly two dozen states have legalized marijuana for medical use. Meanwhile, four states have legalized the recreational, adult use of marijuana since 2012. Long gone are the days where the idea of legalizing marijuana derived 25% or less support from polling the public. Now, you'll find nearly overwhelming support for the legalization of medical marijuana, and a slight bias in favor of legalizing recreational marijuana.

Americans' opinion of marijuana takes a major turn
The latest Gallup poll from 2014 showed that by a margin of 51% to 47% respondents favored marijuana's legalization across the United States. The General Social Survey had similar statistics, with legalization favoring continued federal prohibition by a margin of 52% to 42%.

Source: Washington Marijuana Association, Facebook

If you focus on medical marijuana without the recreational aspects, the call for legalization motors even higher. A Pew Research Center study in 2013 showed that 77% of respondents believed marijuana offered legitimate medical uses, compared to 16% who said no, and 7% who didn't know. A more recent poll from Quinnipiac University showed that respondents in swing states Florida, Ohio, and Pennsylvania would prefer to see marijuana legalized for medical purposes, with 84%, 84%, and 88% of respondents in favor of its legalization, respectively. Since 1960, no presidential candidate has won the presidency without winning two of these three states, meaning medical marijuana could become a hot button issue in the 2016 presidential debate.

Long story short, public opinion on marijuana is rapidly changing, and generally toward a more positive view on the currently illegal drug.

When might marijuana be legalized across the country?
Despite these polls, the future for marijuana, both medically and recreationally, still remains clouded at best.

With this in mind, Selzer & Co., on behalf of Bloomberg, recently conducted a poll that asked more than 1,000 Americans when they believed (if ever) that marijuana would be legalized across the United States (both medical and recreational). Respondents were given seven possible choices, which you can see below.

Source: Bloomberg Politics poll

There are two figures that are particularly striking.

First, pretty much one-third of the people polled don't believe marijuana will ever be fully legalized across all 50 states. Considering these respondents were given an option of selecting "more than 20 years from now," it serves as a stark reminder that some state government leaders and constituents simply likely aren't going to ever be in favor of legalizing marijuana. Period.

Secondly, I believe it's worthwhile to note that while a majority of respondents (63%) do eventually foresee all 50 states legalizing marijuana, a the consensus of that majority believe it will be some time off before that occurs. Just 19% believe it will be within the next five years, while another 26% suggest it'll be somewhere between six and 10 years from now. An additional 18% of respondents opined it would be 11-plus years before marijuana were legalized nationwide.

Although the prospect of marijuana legalization, or marijuana law reform, is great news for a company like GW Pharmaceuticals (NASDAQ:GWPH), which discovers cannabinoids from the cannabis plant and attempts to utilize these cannabinoids to affect positive biologic change, the reality is that the barriers to cannabinoid and marijuana-based research are likely to remain in place by the Food and Drug Administration for some time to come. This isn't devastating news for marijuana-focused pharmaceutical companies like GW Pharma, but it does imply that the length of time it takes to develop potentially game-changing cannabinoid-based drugs won't be shortening anytime soon.

Source: GW Pharmaceuticals

A number of hurdles remain
According to NerdWallet's estimates, sweeping legalization of marijuana could lead to more than $3 billion in extra tax revenue each year for the federal and state governments, combined. But, the reality of achieving this number seems far-fetched, with a number of hurdles still needing to be dealt with.

For example, in Colorado (one of the test states for full marijuana legalization) three-quarters of the jurisdictions within the state still treat marijuana as an illegal substance and have either the recreational aspect of it banned, or both the medical and recreational aspect banned. Even though Colorado voters approved marijuana's statewide legalization in 2012, enforcement of marijuana laws has been complicated by jurisdictions doing as they please. If we were to see a sweeping legalization across the U.S. on a federal level, there's no telling how individual states and jurisdictions who are opposed to marijuana's legalization might react.

Another problem with marijuana's momentum is that it doesn't have the undivided attention of Congress or the president. Even though Quinnipiac University's swing state poll suggests marijuana is becoming a potential campaign issue, President Obama has publicly stated on a few occasions that marijuana simply isn't a top priority of Congress or his administration.

Source: White House on Flickr

Instead, President Obama is suggesting America's youth focus on more pressing global issues instead. In other words, until marijuana becomes a pressing issue, or voters make themselves heard by threatening to vote nonsupporting legislators out of office, then it's unlikely we're going to see legislative changes materialize anytime soon.

Lastly, marijuana's safety remains a primary question. We've witnessed a number of studies in recent years that have suggested marijuana could help patients with type 2 diabetes, aggressive brain cancers, and even Alzheimer's disease. However, in the preceding decades more than nine out of 10 marijuana studies were commissioned with the aim of analyzing its risks, not its benefits. Until more positive data is gathered on marijuana and its newer studies mature, it could be difficult to sway lawmakers to take action.

I personally believe that we do appear to be headed in the direction of an eventual softening of the current federal marijuana laws, but based on these poll results marijuana supporters and investors would be smart to realize that change isn't going to come quickly.