With a few notable exceptions, the American public's opinion on marijuana -- both medical marijuana and recreational, adult use marijuana -- is growing more favorable.

Two decades ago just a quarter of survey respondents would have been in favor of marijuana being legalized, and not a single state had authorized the use of the drug for medical or recreational purposes. Today you can find 23 states that have legalized marijuana for medicinal purposes, four states that have also agreed to let consumers purchase the drug for recreational use, and more than half of the American public favors its across-the-board legalization in both Gallup's and General Social Survey's latest studies. Independent studies on so-called swing states show an even more robust support for medical marijuana, with polls suggesting 70% to 88% approval ratings, depending on the state.

Of course, opposition to marijuana still exists. Although we're seeing support for marijuana from both sides of the political aisle (and without turning this into a political finger-pointing match), Republican-led states tend to be among those left that haven't legalized marijuana either recreationally or for medical purposes.

However, that could be about to change.

Could this be the 24th state to legalize medical marijuana?

Louisiana, within short order, could become the next state to legalize medical marijuana. A fun fact about Louisiana is that medical marijuana was legalized some time back (in 1978 and again in 1991), but the actual laws that relate to growing and distributing the drug were never laid out, making the original legalization something of a moot point.

On top of proposed bills making their way through Louisiana's House and Senate that would alter criminal offenses for people caught with marijuana illegally, SB 143, a bill introduced in the Senate by Fred Mills (R- New Iberia, LA), would give authority to three state boards -- the Louisiana Board of Medical Examiners, the Louisiana Board of Pharmacy, and the Louisiana Department of Agriculture -- to regulate the medical marijuana industry.

If SB 143 passes, patients with a valid medical marijuana prescription could get a non-smokable form of marijuana at one of the state's 10 designated dispensaries, which are to be supplied by a single grower that has yet to be determined. The list of illnesses that would potentially qualify a patient for medical marijuana is relatively short, and includes glaucoma, spastic quadriplegia, and patients undergoing chemotherapy to treat cancer. There is, however, a provision built into the bill that would allow for additional diseases to be reviewed and potentially added later.

Current Louisiana Governor Bobby Jindal (R-LA) has said that he will sign the legislation if it makes it to his desk, as long as there aren't "any minor issues" with the law.

The unique marijuana clause that other states may mimic

What's unique, and what might have other states following in its footsteps, is the attached sunset clause added to SB 143 in the Senate.

A sunset clause is nothing more than an "end date" for a provision or bill unless further legislative action is taken. In SB 143's case, there is a five-year sunset clause built in, meaning Louisiana would have something of a five-year "tryout" period with medical marijuana where it could assess its impact and determine if this program is right for patients and the state. If no additional action is taken to extend the bill, SB 143, should it even become a law in the first place, will simply end five years from the date Gov. Jindal signs it into law.

This actually could become something of the norm that other states which haven't adopted medical marijuana or recreational marijuana laws may consider. The American public is clearly behind some degree of additional freedoms for marijuana use or perhaps decriminalization, but skeptics are worried about the possible negative social impacts of marijuana, or perhaps the effects of its long-term use which are still being studied. A sunset clause allows marijuana to be legalized for a finite period of time upon which legislators can review the data and decide if they'd like to renew the law.

Keep your federal expectations realistic

Although Louisiana could be setting a precedent for other states to follow, don't look for the federal government to jump at the opportunity to utilize a sunset clause for its medical marijuana legislation anytime soon.

For starters, marijuana just isn't a big priority for Congress, or even the President. While Barack Obama has acknowledged the growing support for marijuana and provided some objective insight that getting more states on board would certainly help its chances of a federal approval or decriminalization on a medical basis, he's also urged Americans to focus on more important issues than marijuana. It's a subtle way of saying that this Congress is unlikely to tackle marijuana reform with any expediency.

Additionally, President Obama and presidential hopeful Hillary Clinton have both weighed in with their opinion that all the facts aren't in yet on marijuana. In other words, both would prefer to see additional social and medical tests run that quantify the safety of the product over the long-term before they'd endorse changing its current scheduling status.

More waiting for marijuana investors

In the end, a potential approval in Louisiana is a step forward for potential investors, but it's still not a reason to consider investing in marijuana stocks.

The majority of marijuana stocks trade on over-the-counter bulletin boards, meaning there are few requirements that make these companies report their financial results with any regularity. Sometimes even finding basic information about these penny stock marijuana companies can be difficult.

Among possible marijuana investments, GW Pharmaceuticals (NASDAQ:GWPH) continues to be the most promising -- and "promising" may be a bit of a stretch. This drugmaker, which is using cannabinoids from the cannabis plant to develop drugs, has demonstrated some degree of success with Epidiolex for two rare types of childhood-onset epilepsy, but it's not as if GW Pharmaceuticals is expected to be profitable anytime soon.

I'll say there's definitely momentum among the public for marijuana law change, but it doesn't merit your investment dollars -- at least not yet.