To say there's been a dramatic shift in sentiment toward marijuana over the past decade is an understatement.

In just one decade, the American public went from opposing the legalization of marijuana by a margin of three to one to favoring its legalization by nearly a three-to-two margin, according to statistics from research firm Gallup.

What's fueled this sudden surge in marijuana interest among the public? I'd opine it's been a mixture of the need for states to collect tax revenue to narrow budget deficits and the visibility of the positive effects of medical marijuana coming to light. Medical marijuana is most often prescribed by physicians as a treatment for cancer pain and as an appetite stimulant. There are currently 23 states that have legalized medical marijuana, and four (Oregon, Washington, Colorado, and Alaska) that have legalized the drug for recreational adult use.

You never knew this about marijuana

There's much more to the marijuana debate than whether or not it should be legalized for recreational use. Select drug developers around the world are examining the properties of cannabinoids from the cannabis plant, as well as marijuana itself, to determine whether or not they could have a medically beneficial effect against certain diseases.

Whether you realize it or not, these five diseases may be successfully fought with or cured by marijuana.

1. Brain cancer

Brain cancer is a scary diagnosis because surgery is often difficult, and the blood-brain barrier makes most standard chemotherapy options ineffective.

However, in May, London researchers released a report in Molecular Cancer Therapeutics that showed pretreating brain tumors with the cannabinoids THC and CBD prior to radiation therapy led to a dose-dependent increase in tumor cell death due to heightened radiosensitivity. During the trial, researchers concluded that tumors that were pretreated wound up being just one-tenth the size of tumors in the control group.

Cannabinoid-based drug developer GW Pharmaceuticals (NASDAQ:GWPH) currently has two compounds in clinical development (GWP42002 and GWP42003) for glioma and is the company to watch in this space.

2. Alzheimer's disease

Another serious brain disease is dementia, of which a majority of cases wind up being Alzheimer's disease. According to the Alzheimer's Association, the number of Alzheimer's cases is expected to rise by 176% to 13.8 million by 2050, and this follows a 68% increase between 2000 and 2010.

The good news is, based on a multi-author abstract published in the Journal of Alzheimer's Disease last year, cannabinoid THC may be useful in slowing the formation of beta amyloid, the plaque that floats around in Alzheimer's disease patients' brains that reduces their cognitive function. After examining the effect of THC on beta amyloid protein precursor cells, researchers noted at the six-hour, 24-hour, and 48-hour marks that THC lowered beta amyloid levels.

Although a handful of small studies have been undertaken concerning marijuana's effect on Alzheimer's, no larger drug developers currently have any clinical trials under way in this indication. But, I'd suggest it's certainly one worth closely monitoring considering the limited success of traditional pharmaceuticals in treating Alzheimer's.

3. Epilepsy

Epilepsy is the fourth most common neurological problem, trailing only Alzheimer's, stroke, and migraine. Epilepsy affects about 150,000 people in the U.S. annually, and over their lifetime, people have about a 1-in-26 chance of developing epilepsy.

We don't need to reference abstracts here, though, as GW Pharmaceuticals has produced scintillating early-stage results for Epidiolex in two rare types of childhood epilepsy, Dravet syndrome and Lennox-Gastaut syndrome. As my colleague and biotech guru Brian Orelli recently reported, 56% of Dravet syndrome patients observed their seizure frequency drop in clinical studies, while 52% of patients with drop seizures, often associated with Lennox-Gastaut syndrome, had their seizure frequency reduced.

4. Type 2 diabetes

Diabetes is what you might refer to as a silent killer. Even though it doesn't swiftly kill patients, it is a chronic, lifelong condition that can lead to a number of co-morbidities that can eventually lead to death. Within the U.S., per the Centers for Disease Control and Prevention, there are 29.1 million people with diabetes -- 90% to 95% of which are type 2 diabetics.

Yet, in May 2013 a three-authored study published in The American Journal of Medicine observed that marijuana could play a key role in controlling people's blood sugar levels. The study, which looked at 4,657 people, including both active and former marijuana users, showed that current marijuana users had a 16% reduction in fasting insulin levels and an accompanying 17% drop in HOMA-IR, which measures insulin resistance and beta-cell function. Surprisingly, marijuana users also had slimmer waistlines!

Not to sound like a broken record, but GW Pharmaceuticals is also developing a drug known as GW42004 for type 2 diabetes. In a phase 2a study, it led to a statistically significant reduction in fasting plasma glucose levels with a positive trend of increased insulin sensitivity. Obviously, a drug approval here could have broad treatment implications. GWP42004 is currently in phase 2b trials.

5. Schizophrenia

Lastly, schizophrenia has been diagnosed in about 3.5 million people in the United States, or slightly more than 1% of the population, according to the Schizophrenia and Related Disorders Alliance of America. The costs to treat schizophrenia range from $32.5 billion to $65 billion annually.

In 2012, a study published in Translational Psychiatry hinted that cannabinoid CBD may prove to be an attractive substitute for current antipsychotic treatments. In total, the study examined 39 patients, dosing 20 with CBD and 19 with amisulpride. While both led to similar Brief Psychiatric Rating Scale scores upon study completion, it was noted that the CBD group had fewer side effects than the amisulpride group. Keep in mind that THC, not CBD, is the hallucinogenic component of marijuana.

As should be no surprise by now, GW Pharma is also developing GWP42003 as a potential treatment for schizophrenia. Following positive early-stage results, the drug has moved into phase 2a with a results readout expected in the second half of this year.

One thing to remember

While marijuana has shown very promising benefits in research-driven and clinical studies, we have to keep one thing in mind as investors: Marijuana is still a schedule 1 drug according to the federal government.

Being classified as a schedule 1, or illicit, drug denotes that marijuana has no medical benefits in the view of the government, which could make it extremely difficult for drug developers to advance new studies. The Food and Drug Administration hasn't exactly taken a negative stance on cannabinoid-based medications, but my personal opinion is that it'll be extra critical of approving studies considering the wide scope of conflicting safety data we've witnessed in studies over the past decade. For a company such as GW Pharmaceuticals, it means the possibility of having to jump through more safety hurdles, or maybe even having its drug restricted to a certain subset of patients.

As a consumer, I'm excited about the potential benefits marijuana can offer sufferers of these diseases. But as an investor, I'm still keeping a substantial distance between myself and a still immature and undefined marijuana industry.