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Medical Marijuana: Facts about cannabis, THC, and CBD


Medical Marijuana: Facts about cannabis, THC, and CBD

Exploring medical cannabis means becoming a highly educated consumer. You need to learn as much as you can from a variety of sources. This guide is intended to help you make a more-informed decision. This guide can’t tell you whether medical cannabis will alleviate your health conditions or symptoms. But it will provide basic information to help you consider whether medical cannabis is right for you, ideally working openly with your physician and other health care providers.

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Does cannabis really offer the health benefits you hear so much about?

Or, Is The Hype More than the Hope?

You Decide, With The Expert Information On Every Page Of Medical Marijuana: Facts about cannabis, THC, and CBD​

What You Need To Know From The Most Trusted Source In Health Information—Harvard Health Publishing

Medical cannabis is legal in 33 states and counting.  It’s available in more delivery methods than ever before, including lotions, drops and a variety of edibles, but what exactly does it do?

With so much information and junk-science on the internet, it is important to get solid facts from doctors and scientists you can trust before talking with your doctor to see if medical marijuana could help you. 

Now leading experts at Harvard Medical School are here to help you separate fact from fiction about medical cannabis and CBD so you can make informed decisions. There is evidence for potential benefits for some conditions, and less so for others. And, while there is a lot of positive talk about cannabis, there are risks—especially if you’re over 55.

Harvard Health Publishing’s report, Medical Marijuana: Facts about cannabis, THC, and CBD, will give you the evidence-based answers to when and why you might want to consider medical cannabis. You’ll also learn about how hemp actually works, and how the CBD component of medical marijuana might bring relief without the high.

Download the report right now and get the facts and dispel the rumors! Learn the history and science behind this ancient plant and be well-prepared for a conversation with your doctor.

Prepared by the editors of Harvard Health Publishing in conjunction with Staci Gruber, PhD, Associate Professor of Psychiatry, Harvard Medical School and Director, Cognitive and Clinical Neuroimaging Core, and Director, Marijuana Investigations for Neuroscientific Discovery Program, McLean Hospital. (2020)

About Harvard Medical School Guides

Harvard Medical School Guides delivers compact, practical information on important health concerns. These publications are smaller in scope than our Special Health Reports, but they are written in the same clear, easy-to-understand language, and they provide the authoritative health advice you expect from Harvard Health Publishing.

  • Back to the future
  • Cannabis 101
  • How cannabis affects the mind and body
  • Does medical cannabis work?
  • Medical cannabis options
  • 1When it starts, how long it lasts
  • The CBD craze: Buyer beware
  • Who can get medical cannabis?
  • How to obtain medical cannabis
  • Common safety concerns
  • Long-term health risks
  • Resources

How to obtain medical cannabis

If you want to get permission to legally use medical cannabis under a medical marijuana program, it’s important to fully understand the terms of your state’s medical marijuana law or program. Whether you can access medical cannabis depends on what state you live in. The following information applies specifically to cannabis products obtained under state medical marijuana programs—not to hemp-derived (mostly CBD) products for sale online and in the general marketplace.

Comprehensive programs provide patients with legal protections, practical access to a variety of cannabis preparations, a variety of ways to administer cannabis products, and ongoing, public access to the program.

An additional 15 states have restricted, noncomprehensive programs. Many of these provide access to only low-THC, high-CBD cannabis preparations— for example, to treat seizures.

The National Conference of State Legislatures website maintains a list of state programs with links to the text of the laws themselves. It’s a good place to start educating yourself about medical marijuana laws: research/health/state-medical-marijuana-laws.aspx. Your state, if it has a medical marijuana law, may also have online information about the program. Following are some of the fundamentals of state medical cannabis laws and programs.


Doctors cannot “prescribe” cannabinoid-based products unless they are in the form of one of the four FDA-approved pharmaceuticals. Instead, a health care provider “certifies” you to legally obtain and use medical cannabis. In some states, this may be called getting authorization or a recommendation.

The person providing certification is usually a physician (M.D. or D.O.), who confirms that you have a qualifying condition—a health problem with symptoms that could, hypothetically, be alleviated by cannabis. You’ll probably need it in writing, but some states allow oral consent.

Other health care professionals who can certify in certain states include physician assistants, nurse practitioners, registered nurses, naturopaths, dentists, podiatrists, and nurse midwives. Some states also require a registered pharmacist to be at dispensaries to advise people on the appropriate cannabis preparation and delivery method for their qualifying conditions. You don’t necessarily have to get certified by your usual doctor. In fact, most primary care providers in the United States don’t offer this service. But you can also find physicians who specialize in providing access to medical cannabis. You may see them referred to as “marijuana doctors” or “medical marijuana clinics.”


States require you to be on an official list, or registry, as a certified medical cannabis user. You may be required to obtain a physical card. Or you may need to be added to a database that medical cannabis providers can check. You will probably pay a fee for registration, typically good for one year.

Caregiver access

Medical cannabis laws allow you to designate a primary caregiver. This person is an adult who acts as an intermediary to buy, deliver, and/or administer medical cannabis to certified patients. A caregiver can also grow the cannabis, or help the patient to do it. It can be a family member or friend, but is often a home health care provider or other medical professional.

Where you buy it

Some states allow privately run, for-profit cannabis dispensaries— brick-and-mortar facilities where a certified patient or caretaker can enter and buy products. You generally need to prove that you are certified to enter.

In other states, only nonprofit dispensaries are permitted. Or the state may allow people to obtain medical cannabis from nonprofit “collectives” in which multiple patients band together to produce and provide cannabis to themselves.

Some states allow patients to cultivate a limited number of cannabis plants for medical use.

State laws vary on how much cannabis you can possess at any given time. They may specify either actual ounces of products, an amount to last a certain period (often one month), or a limited number of living plants in cultivation.

Hemp-based products

You do not need to obtain certification to buy and use legally available hemp-based products containing CBD. But always keep in mind that these products are not (yet) regulated for purity and potency. In contrast, most states require that medical cannabis products sold in dispensaries undergo testing.


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