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Drugs & Health Blog

Medicines or Poisons?—Why Cannabinoids Can Both Help and Hurt You

This blog post is archived and is no longer being updated. For the latest content, please visit the main Drugs & Health Blog page.
The NIDA Blog Team

This is the final post of a 3-part series on the science of medical marijuana. Check out Part 1: What’s Wrong with “Medical Marijuana”? and Part 2: Making Medicine from Marijuana.

People who write about the health benefits of marijuana sometimes think it’s ironic that a plant containing compounds that could treat disease (like THC or CBD) is banned by the government for being unsafe. But in fact many effective, FDA-approved medicines are closely related to illegal, harmful drugs and are sometimes even made from the same sources.

That’s because there’s a fine (and sometimes fuzzy) line between chemicals that are good for you and those that can hurt or even kill you. The Greek word pharmakon, where we get pharmacy, originally meant both “medicine” and “poison.”

Speaking the Body’s Language

The opium poppy is a great example. It’s the source of a drug called morphine, part of a class of drugs called opioids. Morphine is used to make heroin, a very addictive and sometimes deadly drug. But morphine is also modified to make many effective, relatively safe pain relievers prescribed widely by doctors and dentists. In fact, these opioids are our most valuable drugs for pain relief.

Another example is cocaine, from the coca plant. It's part of a class of drugs called stimulants. Cocaine is an especially dangerous, addictive stimulant, but it's closely related to medications used to treat people with attention deficit hyperactivity disorder (ADHD) and other conditions.  Sometimes it's also used as an anesthetic.

The thing that makes a drug a drug is its ability to speak the body’s language—specifically, to interact with one of the many chemical signaling systems that cells use to talk to each other. Both heroin and cocaine are able to do that, fluently.

Same with marijuana: Its cannabinoid chemicals speak the body’s own endocannabinoid language.

Parlez-Vous Endocannabinoid?

Nerve cells use chemicals called neurotransmitters to send each other messages, and there are several different kinds of neurotransmitters. Similar chemicals in plants or in foods can interact with these neurotransmitter systems because their molecules are very similar to the ones produced naturally in the human body.

Morphine from the poppy plant is able to work in a peson's nervous system because it closely resembles the body’s own natural pain-relieving opioid chemicals—the endorphins that cause a “runner’s high.” (The “endo” in endorphin or endocannabinoid means “from inside”—that is, inside your body.)

Cocaine and related stimulants work with your own neurotransmitter dopamine, which naturally keeps you focused on rewarding activities.

And the THC in marijuana interacts with the endocannabinoid signaling system used by the body’s own cannabinoid chemicals—such as anandamide—in brain circuits that control a wide range of things including pleasure, memory, thinking, concentration, movement, coordination, and even how you perceive time. That’s why THC can interfere with these abilities when people smoke marijuana either to get high or to treat a medical condition.

The endocannabinoid system also is involved in things like appetite and pain, which is why THC has been made into an effective medication for helping treat nausea and loss of appetite in AIDS and cancer-chemotherapy patients. And it's why THC may, in the future, be prescribed for treating pain.

So, there’s nothing special about marijuana: It’s one of many plants that contain substances that can be both beneficial and harmful, depending on how they're used.

Update: Read the blog post, “How Legal Is Marijuana?

Comments posted to the Drugs & Health Blog are from the general public and may contain inaccurate information. They do not represent the views of NIDA or any other federal government entity.


I think you have reason to do a text on the mariguana that's very dangerous for the kid's and the adult
you are absolutly right
"Morphine is used to make heroin—a very addictive and sometimes deadly drug. But it is also modified and used to make many effective, relatively safe pain relievers prescribed widely by doctors and dentists. In fact, these opioids are our most valuable drugs for pain relief." Do you think perhaps your speaking too kindly about prescription opioids? They can be very addictive and easily abused. ADHD medications (like Adderall) are also often abused by young people and has the potential to become addictive if not used properly. Perhaps you should highlight the fact that these drugs are only "safer" if they're taken as prescribed. Just because we have these very useful legal medications does not mean they are beneficial to everyone or that they cause no harm. This is a complicated subject and you may be simplifying it a bit too much. Teenagers should be aware of legal drugs of abuse as well as illegal drugs of abuse, or they may think it is okay to abuse pain medications or ADHD pills, or other potentially addictive prescribed drugs like benzodiazepines.

Thank you, Julie, for bringing this up.  We agree that prescription drug abuse is dangerous, and recognize that legal drugs don't always mean "safer" drugs.  That's why NIDA developed PEERx, our teen prescription drug abuse prevention program.  Check it out:

man made beer god mad weed in god we trust!
Marijuana can "wake up" a schizophrenia gene in young people, which is devastating for the families.
Woah...didn't know that.
Well analyzed information, thanks for this great post.
I really appreciate your effort you have so obviously put into this content.
You do not have to do drugs man.
I want t study that is not supported or funded by those who want to keep the use of marijuana as a criminal activity and those who want it legalized. I don't want to read it on any site supporting one or the other. I can go with my personal use over the last ~20 years. Wtihin this time, I graduated from high school,I graduated from college in 5 years for my bachelors, Got a job immediately out of school in a professional field. After two years full time I was granted an assistantship in a Mathematics department and earned my Masters in two years. At that point I maintained two job, one full time and one part time for 6 years. I finally returned to school to earn my bachelors, received an assistantship and have maintained a 3.75 GPA. Throughout this time, except for the 4 latter years of my Bachelors degree experience, I smoked all the time. Morning, noon and night, whenever I could. I have had mood issues but I'm also from Sicilian descent and my father has the same disposition and has never done a drug. These past few years, I have turned to prescription drugs to meet the needs of my addictive personality and the extremes I have encountered are ten fold to anything I experienced when using marijuana. But this is not to say that using marijuana has had no effect on my brain or performance, I just have trouble determining what that effect is. I just want an unbiased, give me the facts research. Being that I am a statistician, I have trouble believing studies that are funded by those are on the extreme sides of the debate. That type of research has an agenda instead of a more blind approach. Could you lead me to a study that I speak of? I've search to no avail.
I'm curious about how you feel about Kratom? Considering most websites like these are completely on board with drugs prescribed by doctors, I'm curious about how a website like this feels about natural painkillers? Also, how do you feel about things like salvia divinorum, which are legal, but considered as drugs? Are these plants, or drugs in your opinion?

Hi Anonymous.  Any plant that affects the brain is a drug—and "natural" does not mean harmless.  There are plenty of "natural" substances that are unsafe for humans to use or consume.  "Natural" substances can also produce unwanted side effects.  For example, salvia can cause dizziness and slurred speech, and long-terms effects on learning and memory.  

Also, we wouldn't say we're "completely on board with drugs prescribed by doctors."  NIDA supports the use of prescription painkillers, when used as prescribed by a doctor.  But, we fully recognize the potential for abuse and the dangers that  poses to teens.  We developed the initiative PEERx to help educate teens about the risks of abusing prescription drugs.

tv affects the brain too
ok im 17, ever since elementery school i have had strait f's, i started smoking marijuana senior year. since i started smoking my grades have jumped from strait f's to b's and c's. i now have a 2.93 gpa. im also sure that my brain has been effected. solely because i used to have severe anger issues. since i started smoking my anger has gone to damn near nothing. marijuana is a very effective medicine. the government needs to realize that.
Marijuana is not a medicine if any sorts! It does not matter that senior year you have B's and C's, as you could be taking the easiest class available to make that claim. Clearly, marijuana has not AFFECTED your spelling or grammar, so I will stay away from this harmful, clearly dangerous, drug, unless I feel the need to commit intellectual suicide. No offense, but all of the people that I have ever met who use weed have turned out to be bums on the street, and I feel badly for them. Stop using it and work a bit harder at school, and you'll see even better results.
Bums on the street? Really?.......Really? Why can't we level with kids? I'm not supporting any adgenda other than truth here. Teenagers can see through b.s. just fine and propaganda makes them feel patronized. Insult people's intelligence and they're going to dismiss everything you say.
Now I want to just clear up one question that everyone here is for, more then one actually, is cannabis bad for you? (I know a bunch of people are going to say "YASS IT IZ IT WILL KILLZ U) but I've seen study showing how it does have tar like cigs but using a bong (or something like that, don't smoke by the way) will filter all of it out (probably b.s) and that it can give you medical properties that can help your lungs if you smoke or smoked cigs Next question: how does cannabis affect your mind? I know many people will say the same brainwashed reply "it will make you unmotivated and depressed" but I have searched it and actually it makes you happy (que stoner laugh) and that there are accounts how people who smoke it have actually lived on to have successful lives even after continuing to smoke it. Final question(s): how addictive is cannabis? (by the way, I'm getting tired of people comparing it to meth and acid and other way more harmful drugs) and can you overdose on it (and if you can how many deaths are there) because I'm hearing a ton of 12 year olds going all like "IZ SMOKE WEED EVERYDAY 420! AND IZ SUPA GOOD AND K00L AND ITZ DONT HURTZ YOU" and I want the facts
I am 52year old college graduate and I have seen and believe marijuana does not turn people or kids into stoner dropouts. Those kids that everyone says are stoner dropouts are the same kids that would have and do dropout of our wonderful schools that we have in the United States, that is with a lot of sarcasm, the same schools and teachers that don't see the kid struggling or bored until they start to smoke marijuana. Yes, I have seen a couple of kids that think they need marijuana but they usually outgrow this faze when they "grow- up" . I also think that the substance helps release pain and also have seen it help people to get much better when going through some pretty horrific medical conditions. I have never seen or heard of somebody who just smoked marijuana kill or maul anybody or animal If someone told you that they have heard of this, tell them you are from the show me state so they need some facts or reports to show you.