Cannabis and Cancer
Cannabis has been used for thousands of years for both medical and recreational reasons. Its use is increasing in the United States and around the world. Scientists have studied its effects, how safe it is, where risks are more prominent, and how it might interact with other treatments and medicines.
For people with cancer, cannabis is being studied for its possible benefits in helping to manage certain side effects of cancer and its treatment. But cannabis can be harmful in certain situations, forms, and doses.
Learning how cannabis works and how it can be safely used is important for everyone. In this section, you’ll find information about cannabis and cannabinoids, different forms of cannabis, and how they might be helpful or harmful.
What is cannabis?
Cannabis is a group of plants (genus) in the Cannabaceae family. Cannabis is often bred for its flowering part, known as flower, and there are more than 700 varieties (strains). The different terms used to describe cannabis can refer to different types of cannabis plants or specific parts or chemicals found in a cannabis plant. Understanding these differences can help you make informed decisions about what might be right for you.
What do sativa or indica mean?
Historically, marijuana plants have been classified as Cannabis sativa or Cannabis indica based on their appearance and historical origins. Today, these two labels are often recognized and used in US states where cannabis is legalized.
The product label typically lists what’s inside the package as sativa, indica, or hybrid. However, these labels do not always reliably describe a plant’s chemical makeup or effects. The actual effect of the product depends on the unique chemical makeup of the plants used.
- Cannabis sativa is known for enhancing mood, energy, and mental focus.
- Cannabis indica tends to have a calming, relaxing effect.
- Hybrid cannabis refers to a cannabis plant that has the combined effects of sativa and indica.
Each cannabis plant contains natural chemicals that create the effects a person feels when using cannabis products. These chemicals include cannabinoids and terpenes. Cannabinoids are the reason cannabis affects how your brain works and how your body reacts to using cannabis. Terpenes can help enhance the effects of cannabinoids.
What are THC, CBD, and terpenes?
Cannabis plants are grown to have varying levels of active chemicals like THC, CBD, and terpenes. Your body can be affected by these in different ways.
- THC (delta-9-tetrahydrocannabinol) is a psychoactive cannabinoid chemical. This means it can affect how your brain works. It’s the main ingredient in marijuana and other cannabis products that produce a feeling of being “high.” Some people describe this as a sense of euphoria or extreme happiness.
- CBD (cannabidiol) is a cannabinoid that can change how you feel pain and how your body responds to inflammation from an injury or a health problem. It can also create a feeling of relaxation. CBD does not cause the “high” that THC is known for.
- Terpenes are not cannabinoids. They are another type of natural chemical that gives many plants, including cannabis, their unique smell and flavor—like citrus or pine. Terpenes don’t cause a “high” on their own but can interact with chemicals like THC and CBD to shape the psychoactive effects of each cannabis strain. For example, some terpenes may help make the “high” more relaxing or more energizing.
When cannabinoids and terpenes are combined, the resulting effect is often referred to as the entourage effect. This refers to the idea that all the natural parts of the cannabis plant — like THC, CBD, and terpenes — work better together than they do alone. The combined effects may be stronger or more helpful for things like pain, anxiety, or sleep.
What are marijuana and hemp?
Marijuana is any cannabis plant with flowers that contain more than 0.3% THC. It goes by many names, pot, grass, weed, flower, bud, tree, ganja, and many others. Marijuana is considered illegal by federal law, even though some states have legalized it. Read more in Is Cannabis Legal in the US?
Hemp is any cannabis plant with flowers that contain less than 0.3% THC. This means consumption of hemp products will not produce the “high” associated with cannabis. Other parts of the hemp plant, including the stalks and leaves, may be used for industrial purposes. Hemp is not considered illegal by federal law due to its low concentration of THC.
What cannabis products are available?
Cannabis products come in a variety of forms and can be used in different ways. The most common forms of cannabis are inhaled (breathed in) or ingested (eaten or swallowed). Cannabis is also available in topical (through the skin) and sublingual (under the tongue) forms.
Cannabis products can vary in how they affect you in the following ways:
- Onset of action: How quickly the effects start
- Peak effects: How quickly the effects reach their strongest point
- Duration of effects: How long the effects are felt
These effects can vary based on:
- What form is used
- The chemicals (THC, CBD, and terpenes) in the product
- The way your body responds to cannabis
Inhaled cannabis can be smoked using a rolled joint, pipe, bong, blunt, or another device. Cannabis concentrate can also be "vaped" in e-cigarette devices (vape pens), vaporizers, or other devices.
When cannabis is inhaled, the cannabinoid chemicals enter the lungs, are absorbed by the bloodstream, and go to the brain quickly. The psychoactive effects of THC are felt almost right away. The effects of inhaled cannabis fade faster than ingested cannabis (edibles).
It’s important to know that smoke produced from inhaling cannabis has many of the same cancer-causing chemicals found in tobacco smoke and can cause lung problems. For this reason, most doctors who recommend cannabis for medical reasons prefer that it be taken through a form other than inhaling.
- Onset of action: 0-10 minutes
- Peak effects: 3-10 minutes
- Duration of effects: 2-6 hours
- Possible side effects:
- Cough
- Mouth irritation and dryness
- Sore throat
- Dizziness
- Over-ingestion of high THC (possible overdose)
Learn more about long-term effects of cannabis.
Cannabis can also be taken by eating, chewing, or drinking cannabis products, called edibles. Examples of edibles are pills, tablets, capsules, gummies, candy, chocolates, cooking oils, drinks (seltzer, soda), and baked goods (biscuits, brownies, cookies, etc.).
It can take up to a few hours to feel the effects of edible cannabis. If you eat more fatty foods or drinks around the same time you use edible cannabis, the onset can be longer and the duration can be shorter. It’s important not to take more than the recommended dose, even when the effects of edible cannabis aren’t felt right away. This can lead to a person getting too much THC, feeling effects for longer, and might cause symptoms of overdose.
- Onset of action: 1-3 hours
- Peak effects: 1-2 hours
- Duration of effects: 6-12 hours
- Possible side effects:
- Unpleasant taste
- Increased nausea
- Dry mouth
- Dizziness
- Over-ingestion of high THC (possible overdose)
Learn more about long-term effects of cannabis.
Sublingual cannabis is placed under your tongue. Sublingual products can come in liquid or tincture form or as a dissolvable tablet. They are absorbed fairly fast, so their effects are usually felt more quickly than cannabis edibles.
- Onset of action: 15 minutes-1 hour
- Peak effects: 45 minutes
- Duration of effects: 4-6 hours
- Possible side effects:
- Unpleasant taste
- Dry mouth
- Dizziness
- Over-ingestion of high THC (possible overdose)
Learn more about long-term effects of cannabis.
Topical cannabis is applied directly to the skin, typically for pain relief. The effects are felt in the area where they are applied. They do not cause the “high” associated with other forms of cannabis. These products include cannabis oils, gels, salves, creams, and patches.
- Onset of action: 5 minutes-2 hours
- Peak effects: Varies
- Duration of effects: Varies
- Possible side effects or harms include a rash or other skin irritation.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
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Last Revised: July 11, 2025
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