By Dr. Sanjay Gupta, CNN Chief Medical Correspondent

(CNN) -- Dear Honorable Jeff Sessions,

I feel obligated to share the results of my five-year-long investigation into the medical benefits of the cannabis plant. Before I started this worldwide, in-depth investigation, I was not particularly impressed by the results of medical marijuana research, but a few years later, as I started to dedicate time with patients and scientists in various countries, I came to a different conclusion.

Not only can cannabis work for a variety of conditions such as epilepsy, multiple sclerosis and pain, sometimes, it is the only thing that works. I changed my mind, and I am certain you can, as well. It is time for safe and regulated medical marijuana to be made available nationally. I realize this is an unconventional way to reach you, but your office declined numerous requests for an interview, and as a journalist, a doctor and a citizen, I felt it imperative to make sure you had access to our findings.

Mr. Sessions, there is an added urgency, as we are in the middle of a deadly opioid epidemic that has been described as the worst self-inflicted epidemic in the history of our country.

The drug overdose scourge claimed about 68,000 US lives in 2017, just over 45,000 of them from opioids alone. Every day, 115 Americans die from opioid overdoses. It has fueled a decline in an entire country's life expectancy and will be remembered as a sad and tragic chapter in our collective history.

These are desperate times, and while some may consider making medical marijuana widely available to be a desperate measure, the evidence has become increasingly clear of the important role cannabis can have.

We have seen real-world clues of medical marijuana's benefits. Researchers from the Rand Corp., supported by the National Institute on Drug Abuse, conducted "the most detailed examination of medical marijuana and opioid deaths to date" and found something few initially expected. The analysis showed an approximately 20% decline in opioid overdose deaths between 1999 and 2010 in states with legalized medical marijuana and functioning dispensaries.

It's not the first time this association between medical marijuana and opioid overdose has been found. Though it is too early to draw a cause-effect relationship, these data suggest that medicinal marijuana could save up to 10,000 lives every year.

The science of weed

Cannabis and its compounds show potential to save lives in three important ways.

Cannabis can help treat pain, reducing the initial need for opioids. Cannabis is also effective at easing opioid withdrawal symptoms, much like it does for cancer patients, ill from chemotherapy side effects. Finally, and perhaps most important, the compounds found in cannabis can heal the diseased addict's brain, helping them break the cycle of addiction.

Mr. Sessions, there is no other known substance that can accomplish all this. If we had to start from scratch and design a medicine to help lead us out of the opioid epidemic, it would likely look very much like cannabis.

A better, and safer, way to treat pain

The consensus is clear: Cannabis can effectively treat pain. The National Academies of Sciences, Engineering, and Medicine arrived at this conclusion last year after what it described as the "most comprehensive studies of recent research" on the health effects of cannabis.

Furthermore, opioids target the breathing centers in the brain, putting their users at real risk of dying from overdose. In stark contrast, with cannabis, there is virtually no risk of overdose or sudden death. Even more remarkable, cannabis treats pain in a way opioids cannot. Though both drugs target receptors that interfere with pain signals to the brain, cannabis does something more: It targets another receptor that decreases inflammation -- and does it fast.

I have seen this firsthand. All over the country, I have met patients who have weaned themselves off opioids using cannabis. Ten years ago, attorney Marc Schechter developed a sudden painful condition known as transverse myelitis, an inflammation of the spinal cord. After visiting doctors in several states, he was prescribed opioids and, according to our calculations, consumed approximately 40,000 pills over the next decade. Despite that, his pain scores remained an eight out of 10. He also suffered significant side effects from the pain medication, including nausea, lethargy and depression.

Desperate and out of options, Schechter saw Dr. Mark Wallace, head of University of California, San Diego Health's Center for Pain Medicine, where he was recommended cannabis. Minutes after he took it for the first time, Schechter's pain was reduced to a score of two out of 10, with hardly any side effects. One dose of cannabis had provided relief that 40,000 pills over 10 years could not.

Using marijuana to get off opioids

For Schechter, as with so many others, the seemingly insurmountable barrier to ending his opioid use was the terrible withdrawal symptoms he suffered each time he tried. When a patient stops opioids, their pain is often magnified, accompanied by rapid heart rate, persistent nausea and vomiting, excessive sweating, anorexia and terrible anxiety.

Here again, cannabis is proven to offer relief. As many know, there is longstanding evidence that cannabis helps chemotherapy-induced symptoms in cancer patients, and those symptoms are very similar to opioid withdrawal. In fact, for some patients, cannabis is the only agent that subdues nausea while increasing appetite.

Why we can't 'just say no' to opioids

Finally, when someone is addicted to opioids, they are often described as having a brain disease. Yasmin Hurd, director of the Addiction Institute at Mount Sinai in New York City, showed me what this looks like in autopsy specimens of those who had overdosed on opioids. Within the prefrontal cortex of the brain, she found damage to the glutamatergic system, which makes it difficult for neural signals to be transmitted. This is an area of the brain responsible for judgment, decision-making, learning and memory.

Hurd told me that when an individual's brain is "fundamentally changed" and diseased in this manner, they lose the ability to regulate opioid consumption, unable to quit despite their best efforts -- unable to "just say no."

It is no surprise, then, that abstinence-only programs have pitiful results when it comes to opioid addiction. Even the current gold standard of medication-assisted treatment, which is far more effective, still relies on less-addictive opioids such as methadone and buprenorphine. That continued opioid use, Hurd worries, can cause ongoing disruption to the glutamatergic system, never allowing the brain to fully heal. It may help explain the tragic tales of those who succeed in stopping opioids for a short time, only to relapse again and again.

This is precisely why Hurd started to look to other substances to help and settled on nonpsychoactive cannabidiol or CBD, one of the primary components in cannabis. Hurd and her team discovered that CBD actually helped "restructure and normalize" the brain at the "cellular level, at the molecular level." It was CBD that healed the glutamatergic system and improved the workings of the brain's frontal lobes.

This new science sheds lights on stories like the one I heard from Doug Campbell of Yarmouth, Maine. He told me he had been in and out of drug rehab 32 times over 25 years, with no success. But soon after starting cannabis, he no longer has "craving, desire and has not thought about (opioids) at all, period."

For the past 40 years, we have been told that cannabis turns the brain into a fried egg, and now there is scientific evidence that it can do just the opposite, as it did for Campbell. It can heal the brain when nothing else does.

I know it sounds too good to be true. I initially thought so, as well. Make no mistake, though: Marc Schechter and Doug Campbell are emblematic of thousands of patients who have successfully traded their pills for a plant.

These patients often live in the shadows, afraid to come forward to share their stories. They fear stigma. They fear prosecution. They fear that someone will take away what they believe is a lifesaving medication.

Where do we go from here?

Mr. Sessions, Dr. Mark Wallace has invited you to spend a day seeing these patients in his San Diego clinic and witness their outcomes for yourself. Dr. Dustin Sulak could do the same for you in Portland, Maine, as could Dr. Sue Sisley in Phoenix. Staci Gruber in Boston could show you the brain scans of those who tried cannabis for the first time and were then able to quit opioids. Dr. Julie Holland in New York City could walk you through the latest research. All over the country, you will find the scientists who write the books and papers, advance the science and grow our collective knowledge. These are the women and men to whom you should listen. They are the ones, free of rhetoric and conjecture, full of facts and truth, who are our best chance at halting the deadly opioid epidemic.

Making medicinal marijuana available should come with certain obligations and mandates, just as with any other medicine. It should be regulated to ensure its safety, free of contamination and consistent in dosing. It should be kept out of the hands of children, pregnant women and those who are at risk for worse side effects. Any responsible person wants to make sure this is a medicine that helps people, not harms.

Recently, your fellow conservative John Boehner changed his mind after being "unalterably opposed" to marijuana in the past. If you do the same, Mr. Attorney General, thousands of lives could be improved and saved. There is no time to lose.