Cannabis does not treat every organ the same way, and how you take it matters more than which strain it is. Smoke is hardest on the lungs. Edibles hand the work to the liver. The heart reacts within minutes however the THC gets in, and the brain is the organ where your age makes the biggest difference.
This page goes organ by organ. For each one we say what the public health sources linked below report, and where they admit the evidence runs out. We are not doctors, and none of this is medical advice. If you have a heart or lung condition, are pregnant or take prescription medication, talk to a clinician who knows your history.
| Organ | What the sources say | Who it matters most for |
|---|---|---|
| Lungs | Smoke injures the airways and is tied to chronic bronchitis | Anyone who smokes it |
| Brain | Short-term effects on memory, attention and coordination; possible lasting effects when use starts young | Teenagers and people under 25 |
| Heart | Faster heartbeat and higher blood pressure right after use | People with heart disease |
| Liver | Turns eaten THC into a second active compound | Anyone taking edibles |
| Gut | A small number of heavy long-term users develop severe cyclic vomiting | Daily users of many years |
| Reproductive system | Advice against any use in pregnancy; one study links regular use to lower sperm counts | People who are pregnant or trying to conceive |
Why the route matters
Smoked or vaped THC reaches the blood through the lungs almost at once. Marilyn Huestis’s 2007 review of how the body handles cannabinoids, written at the U.S. National Institute on Drug Abuse, describes a controlled study in which THC showed up in plasma after the first puff and peaked about nine minutes into smoking.
Eaten THC is absorbed through the gut and passes through the liver before it reaches the rest of the body. The same review puts the peak at one to five hours after an oral dose, lower than after smoking and longer lasting. Most of the differences on this page follow from that.
Lungs
The American Lung Association does not hedge on this one. Its page, last updated in July 2025, says smoking marijuana damages the lung. Marijuana smoke carries many of the same toxins, irritants and carcinogens as tobacco smoke, and it injures the cells that line the large airways. Regular smokers report the symptoms of chronic bronchitis: a lasting cough, phlegm and wheezing.
Vaping is not a clean way out. The association says little is known about inhaling cannabis by any method other than smoking, and that vape pens used with concentrates may cause breathing problems similar to those seen with e-cigarettes. It also says nobody should be exposed to secondhand marijuana smoke, children in particular.
Brain
The brain is where THC does what people take it for, and it is also where the timing of use matters most. The CDC says cannabis used within the past 24 hours affects thinking, attention, memory, coordination and the sense of time, in adults as well as young people. That is the reason driving high is illegal everywhere.
The longer-term worry is about young users. According to the CDC the brain keeps developing until around age 25, and using cannabis before 18 may affect how it builds the connections used for attention, memory and learning. The agency is careful about how far it goes: it says those effects may be long lasting or even permanent, that more research is needed, and that some of what studies pick up could come from genetics or home environment instead of cannabis.
Heart
The heart responds fast. The CDC says cannabis can make the heart beat faster and raise blood pressure immediately after use, and that it may raise the risk of stroke, heart disease and other vascular disease.
Harvard Health adds a sharper figure. Research suggests the risk of a heart attack is several times higher than normal in the hour after smoking marijuana. It describes weaker evidence tying use to atrial fibrillation and ischemic stroke.
One caveat comes from the CDC itself. Most of the studies behind these warnings looked at people who smoked, so it is hard to separate what THC does from what smoke does. For a healthy young adult the extra load is usually tolerated. For someone with heart disease it is a reason to ask a cardiologist before using at all.
Liver
If you smoke, most THC reaches your brain before your liver sees it. If you eat it, the liver goes first, and it changes the drug. Enzymes in the liver, mainly one called CYP2C9, convert THC into 11-hydroxy-THC. The Huestis review describes that compound as equal in potency to THC and reports one study in which it appeared to enter the brain more readily.
The amounts are very different by route. After smoking, the level of 11-hydroxy-THC in the blood is roughly a tenth of the THC level. After an oral dose it is similar to the THC level or higher. That is the chemistry behind the familiar report that an edible feels different from a joint and lasts longer.
The liver is also why edibles are hard to dose. The review puts the share of an oral dose that reaches the bloodstream at between 4 and 20 percent, which is a wide range from one person to the next. The CDC says edibles can take 30 minutes to 2 hours to be felt, and that people who eat more while they wait are a common source of poisonings. Our THC calculator turns a label percentage into milligrams, and our cannabutter guide walks through the math for homemade edibles.
None of the sources on this page list liver damage among the established harms of cannabis. The liver earns its place here because of what it does to the dose. The same enzyme families also process many prescription medicines, which is one more reason to tell your doctor or pharmacist what you use.
Stomach and gut
THC has a long medical history as an anti-nausea drug. Dronabinol, a synthetic THC, has been an FDA-approved treatment for nausea from chemotherapy since 1985.
In a small number of heavy users it does the opposite. Cannabinoid hyperemesis syndrome, or CHS, causes repeated bouts of severe nausea, vomiting and belly pain in people who have used cannabis daily for years. Cedars-Sinai says symptoms usually start after 10 to 12 years of chronic use. Many people with CHS find that hot showers ease the nausea, and doctors treat that habit as a clue to the diagnosis. Hospital care can manage an episode. The only thing that ends the condition is stopping cannabis completely, and the symptoms tend to return if use starts again.
Reproductive system and pregnancy
The CDC advises against using cannabis in any form during pregnancy, whether smoked, vaped, eaten or applied to the skin. THC passes from mother to baby, and some research links use during pregnancy to lower birth weight and to later problems with attention, memory and behavior in children. THC also passes into breast milk. Because it is stored in body fat and released slowly, a baby can be exposed after the mother has stopped, so the agency encourages breastfeeding mothers to avoid cannabis altogether.
For men, the most cited evidence is a 2015 study of 1,215 Danish men aged 18 to 28, published in the American Journal of Epidemiology. Those who smoked marijuana more than once a week had a sperm concentration 28 percent lower than those who did not. That is an association in one population, and it does not show that cannabis was the cause.
So which organ takes the biggest hit?
For anyone who smokes, the lungs. The Lung Association’s statement is the least qualified of any on this page. If you switch to edibles you spare your lungs and take on a dosing problem instead, because the liver makes the effect slower, stronger and harder to predict. For teenagers the answer is the brain. For people with heart disease it is the heart, in the first hour after use.
If you are buying in New York, licensed dispensaries sell products that are lab tested and labeled with THC content, which at least tells you the dose you are starting from. You can confirm a shop is licensed with our New York dispensary license checker.
Frequently asked questions
Which organ does weed affect the most?
It depends on how you take it. For people who smoke, the lungs: the American Lung Association says plainly that smoking marijuana damages the lung. For people who eat it, the lungs are spared and the liver does the processing. For teenagers the main concern is the brain, which the CDC says keeps developing until around age 25.
Are edibles easier on the body than smoking?
They are easier on the lungs, because nothing is inhaled. They are harder to dose. The CDC says edibles can take 30 minutes to 2 hours to be felt, and people who eat more while they wait are a common cause of cannabis poisoning.
Does weed raise your heart rate?
Yes. The CDC says cannabis can make the heart beat faster and raise blood pressure right after use. Harvard Health reports research suggesting the risk of heart attack is several times higher than normal in the hour after smoking.
What is cannabinoid hyperemesis syndrome?
CHS is a condition in long-term daily users that causes repeated bouts of severe nausea, vomiting and belly pain. Hot showers ease the symptoms for many people. According to Cedars-Sinai, the only thing that ends it is stopping cannabis completely.
Can cannabis affect fertility or pregnancy?
The CDC advises against using cannabis in any form during pregnancy and while breastfeeding. In men, a 2015 study of 1,215 young Danish men linked smoking more than once a week to a 28 percent lower sperm concentration, an association that does not prove cause.
Sources
- American Lung Association, Marijuana and Lung Health (updated July 16, 2025)
- CDC, Cannabis and Brain Health
- CDC, Cannabis and Heart Health
- CDC, Cannabis and Poisoning
- CDC, Cannabis and Pregnancy
- Harvard Health Publishing, Marijuana and heart health: What you need to know
- Huestis MA, Human Cannabinoid Pharmacokinetics, Chemistry and Biodiversity, 2007
- Cedars-Sinai, Cannabinoid Hyperemesis Syndrome
- Association Between Use of Marijuana and Male Reproductive Hormones and Semen Quality, American Journal of Epidemiology, 2015
Updated Oct 10, 2026: this article was rewritten against the sources above. An earlier version gave heart rate percentages we could not trace to a source and cited a paper on liver metabolism that turned out to be about something else. Both have been removed, along with the infographic.
For adults 21 and over. Nothing on this page is medical advice.
The Just Weed Strains editorial team writes our strain profiles and consumer guides. Strain profiles summarize publicly available information, including breeder and dispensary descriptions. Effects vary from person to person, and nothing on this site is medical advice.