Overview

Cannabis (marijuana) is a plant called Cannabis sativa. It contains hundreds of chemicals that can have effects in the body. Some of these chemicals, such as tetrahydrocannabinol (THC), are psychoactive and can cause brain-altering effects that make you feel “high.” There is interest in using cannabis for many reasons, but its benefits for most uses are not well defined. Cannabis is available in many strains and forms that each contain different chemicals, so its effects are unpredictable. Common side effects include problems thinking clearly, dizziness, sleepiness, hallucinations, intense feelings, paranoia, and fear. Serious side effects are less common but include dependence and withdrawal, psychotic-like behavior, and a condition called cannabinoid hyperemesis syndrome (CHS). Before using cannabis, make sure to tell your health care provider about any health conditions you have or medicines you are taking.

Uses

What is cannabis used for?

Cannabis is used recreationally to improve mood or feel “high.” It is also used for many health reasons, although its benefits for any use are not well defined. Some common reasons for using cannabis include the following.

• For mental health problems, including anxiety, depression, and posttraumatic stress disorder (PTSD)
• For nausea or vomiting from various causes
• For nerve or muscle pain
• To help manage stress
• To increase appetite, especially in people with serious illness, such as cancer or AIDS

If you are having symptoms of a mental health problem, do not try to treat these symptoms on your own. Talk to your health care provider about your treatment options. If you are already taking medicine for a mental health problem, talk to your health care provider before using cannabis. Cannabis can interact with many medicines. There is also some concern that using cannabis may worsen certain health problems, such as depression, in some people.

Note: Cannabis is not approved by the FDA for any use. The FDA also does not consider cannabis to be a legal dietary ingredient in the U.S. It is a schedule I controlled substance, which means that it does not have an acceptable medical use and has a high risk for misuse. Learn more about the legal status of cannabis here.

Many U.S. states have legalized recreational cannabis or allow its use for specific medical purposes (“medical marijuana”). Learn more about the legal status of cannabis in each state here.

How does cannabis work (mechanism of action)?

Cannabis, or marijuana, is a plant called Cannabis sativa. Products made from this plant contain its flowers, stems, seeds, and leaves. There are hundreds of unique strains of cannabis available on the market. Each of these strains contains different amounts of the many chemicals in cannabis that have effects in the body.

The most well-known chemicals in cannabis are called cannabinoids. Any given strain of cannabis may contain varying amounts of over 100 different cannabinoids. Some cannabinoids, such as delta-9-tetrahydrocannabinol (THC), are psychoactive, which means that they cause brain-altering effects that can make you feel “high.” But most cannabinoids, such as cannabidiol (CBD), are considered nonpsychoactive and do not cause brain-altering effects. Cannabis also contains other important chemicals, called terpenes, that are responsible for its distinctive smell. Some terpenes may also have effects in the body.

Each cannabinoid has its own unique effects in the body and brain. Individual cannabinoids can also interact with other cannabinoids, increasing or decreasing their effects. Since the amount of each chemical in a specific cannabis product or strain varies, the effects of cannabis also vary by batch and strain and how you use it. This makes it difficult to know whether a specific cannabis product will be helpful for treating or managing any medical condition.

Many people who use cannabis report improvement in various symptoms, including pain, anxiety, nausea, and stress. A small number of studies also show that specific cannabis products, which contain a standardized amount of THC, CBD, and other cannabinoids, may be helpful for certain uses. Although many strains of cannabis are marketed for various medical purposes, in most cases, there is not enough research to confirm whether they are truly beneficial.

Although cannabis comes from the same plant as hemp, these two products are very different. Hemp is made from a different variety of Cannabis sativa. According to the U.S. law, hemp products cannot contain more than 0.3% THC. Any product that contains more than 0.3% THC is classified as cannabis. Hemp does not contain enough THC to cause psychoactive effects or make you feel high.

How should I store cannabis?

You should store cannabis according to the product label. Most herbal products should be kept in a cool, dry location that is out of the reach of children and pets and not in direct sunlight.

Side Effects

What are the most common side effects of cannabis?

The most common side effects of cannabis are listed below. These side effects may vary depending on the dose or the specific product you are using and how you use it. Tell your health care provider if you have any of these side effects that bother you.

• Abnormal thinking
• Cannabinoid hyperemesis syndrome (see below)
• Dizziness
• Feelings of intense happiness or joy
• Hallucinations (see below)
• Paranoia or fear
• Sleepiness

There may be other side effects of cannabis that are not listed here. Contact your health care provider if you think you are having a side effect of an herbal product. In the U.S., you can report side effects to the FDA at www.safetyreporting.hhs.gov or by calling 888-SAFEFOOD (888-723-3366). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of cannabis?

While less common, the most serious side effects of cannabis are described below, along with what to do if they happen.

Severe Allergic Reactions. Cannabis may cause allergic reactions, which can be serious. Stop using cannabis and get help right away if you have any of the following symptoms of a serious allergic reaction.

• Breathing problems or wheezing
• Racing heart
• Fever or general ill feeling
• Swollen lymph nodes
• Swelling of the face, lips, mouth, tongue, or throat
• Trouble swallowing or throat tightness
• Itching or skin rash
• Bumps on the skin called hives that can be red, pink, white, or brown depending on your skin tone
• Nausea or vomiting
• Dizziness, feeling lightheaded, or fainting
• Stomach cramps
• Joint pain

Problems Thinking Clearly. Cannabis can change your mental function and affect your ability to think clearly. Tell your health care provider if you notice any of the following symptoms while using cannabis.

• Confusion
• Increased sleepiness
• Trouble remembering things
• Unable to concentrate

Cannabinoid Hyperemesis Syndrome.Some people who use cannabis or cannabinoids may develop a condition called cannabinoid hyperemesis syndrome (CHS). This condition can happen at any time while using cannabis and may be more likely in people who have regularly used cannabis for more than a year. CHS causes severe nausea, vomiting, and stomach pain. This can lead to dehydration and changes in electrolyte levels that can be life-threatening. If you have severe nausea or vomiting that does not go away, get medical help right away. If you think you may have CHS, speak with your health care provider. Stopping all use of cannabis or cannabinoids is the only known cure for CHS.

Dependence and Withdrawal Reactions.Some people who use cannabis may develop physical dependence, which means your body comes to rely on it. This risk may be higher in people who use cannabis regularly for multiple months. If you stop cannabis suddenly, it could lead to withdrawal symptoms. If you have been using cannabis regularly for a while, do not stop using it abruptly. Your health care provider may be able to help you stop cannabis in a way that will reduce the risk of withdrawal reactions. Speak with your health care provider if you have any of the following symptoms of cannabis withdrawal.

• Headaches
• Sweating
• Nausea, vomiting, or stomach pain
• Irritability, anger, or aggression
• Nervousness or anxiety
• Sleep problems or restlessness
• Changes in appetite or weight
• Depression or low mood

Hallucinations or Psychotic-Like Behaviors. Cannabis may cause hallucinations or psychotic-like behaviors. This risk may be higher in people who use high doses of cannabis or people who also use street drugs. Tell your health care provider right away if you have any of the following symptoms or have been told by others you have these symptoms.

• Hearing, seeing, smelling, tasting, or otherwise perceiving things that others do not
• Delusional thoughts, such as false beliefs that you are being controlled
• Disorganized thoughts, such as jumping between topics or having a hard time focusing
• Sudden decline in self-care, such as personal hygiene or academic/work performance
• Aggressive behavior

Heart Attack and Stroke. Smoking or inhaling cannabis can increase your risk of a heart attack or stroke that can lead to death. This risk is higher in people who already have heart disease and those who smoke cannabis regularly for a long time. If you have had a recent heart attack, speak with your health care provider before using cannabis. Get emergency help if you have any of the following symptoms of a heart attack or stroke.

• Chest pain or pressure
• Fast or abnormal heartbeat
• Trouble breathing
• Pain in your back, jaw, throat, or arm
• Sweating, upset stomach, vomiting, or dizziness
• Sudden weakness on one side of your body
• Sudden and severe headache
• Slurred speech or trouble understanding speech

Precautions

Who should not use cannabis?

Allergies to Ingredients. People who are allergic to any of the following should not use cannabis.

• Cannabis
• Cannabis sativa
• Marijuana (or street names, such as Mary Jane, MJ, or weed)
• Any of the ingredients in the specific product

Ask your health care provider if you are not sure what ingredients are in a cannabis product.

What should I know about cannabis before using it?

The U.S. federal government does not consider cannabis to be a legal ingredient. It is a schedule I controlled substance, which means that it does not have any approved medical uses and is at high risk for misuse. Some U.S. states have legalized cannabis or allow its use for specific medical purposes (“medical marijuana”). Cannabis products are available for purchase at registered businesses in these states. These products are not regulated and have not been tested to confirm that they contain the ingredients stated on their labels.

Cannabis is a controlled substance because it can be misused. If you will store cannabis at home, store it in a safe place.

Keep cannabis out of the reach of children and animals. Even small amounts of cannabis can cause serious health problems in children. If your child takes any products that contain cannabis, get medical help right away. Cannabis can also be toxic to pets, including cats and dogs. If your pet eats a product that contains cannabis, call your vet, emergency animal clinic, or animal poison control center right away.

Cannabis can affect your alertness or coordination. Do not drive or do other activities that require alertness or coordination until you know how cannabis affects you.

People who are under the age of 18 or over the age of 65 can be at greater risk for some side effects from cannabis. Talk to your health care provider about your risks if you are in either of these age groups.

If you use cannabis on a regular basis, do not stop using it abruptly. Stopping too quickly may cause serious side effects. See the Side Effects section for more details.

Herbal products, such as cannabis, naturally contain many chemicals. The amount of each chemical in a specific cannabis product can change for many reasons, including the area where the plant was grown, the weather during growth, the time of year when it was harvested, and the way that the plant was processed after it was harvested. If you switch to a new bottle or a different brand, you may not have the same effects or side effects because of this variability. Talk to your health care provider if you have questions or concerns.

Cannabis is available in many forms, including edibles (foods), gummies, liquid extracts, dried and ground powder, tea, and more. It is also inhaled by smoking or vaping, and it is available in patches, creams, and other products that are applied to the skin. Each of these forms may contain different amounts of the chemicals that are naturally found in the plant. Your body may respond differently to cannabis when it is taken by mouth or inhaled. It is not clear if cannabis can be absorbed into the body through the skin.

Cannabis is a type of plant known as a phytoremediator, meaning that it is able to pull toxins and heavy metals out of the soil where it grows. These toxins and heavy metals are pulled into the plant and may be found in products made from the plant. This means that cannabis products may be at high risk of contamination with heavy metals and other harmful chemicals.

What should I tell my health care provider before using cannabis?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if cannabis is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions.Tell your health care provider if you have any of the following.

• A genetic condition that affects how your body processes medicines, such as a CYP2C9 polymorphism
• Drink large amounts of alcohol
• Heart problems
• High or low blood pressure
• Liver problems
• Mental health problems, such as depression, a past suicide attempt, anxiety, hallucinations, paranoia, or psychosis
• Seizures
• Substance use disorder, including cocaine, methamphetamine, or opioid use disorder
• Upcoming surgery or medical procedure

Other Medicines and Supplements.Cannabis may interact with other medicines and supplements. Before using cannabis, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. Cannabis may cause harm to a fetus. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. Cannabis passes into breast milk and may continue to pass into breast milk for weeks after use. This may cause harm to your baby. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does cannabis interact with foods or drinks?

There are no known interactions between cannabis and foods or drinks.

It is unknown if drinking alcohol will affect cannabis. But the risk of serious side effects may be increased if you drink alcohol while using cannabis. It is best to limit the amount of alcohol you drink.

Does cannabis interact with medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before using cannabis.

• Any medicine that causes dizziness and sleepiness, such as prescription pain medicines, sleep medicines, or medicines for anxiety
• Any medicine that can affect your blood pressure or heart rate
• A barbiturate, such as butalbital, phenobarbital, or primidone, which is a medicine that may be used to treat insomnia, migraines, or seizures
• A benzodiazepine, such as clonazepam (Klonopin), diazepam (Valium and others), or lorazepam (Ativan and others), which is a medicine used for anxiety, muscle spasms, or seizures
• A muscle relaxant, such as carisoprodol (Soma), cyclobenzaprine, metaxalone, or tizanidine (Zanaflex)
• An opioid, such as codeine, fentanyl, morphine, oxycodone, or tramadol, which is a medicine used to treat certain types of pain
• Street drugs, such as cocaine, heroin, or methamphetamine

Many other medicines may alter the blood levels of cannabis, and vice versa. Tell your health care provider about all medicines that you take or have recently taken.

The interactions between cannabis and medicines are not fully understood. As with most herbal products, the research on drug interactions with cannabis is incomplete. Always check with your health care provider before using cannabis with any medicines.

Dosing

What should I do if I accidentally use too much cannabis?

If you or someone else has used too much cannabis, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

Cannabis comes in many forms and can be used in many ways. Some people have had physical dependence while using cannabis, which means their bodies come to rely on it. Stopping cannabis suddenly can lead to withdrawal. Read the product label closely, and speak with a health care provider before using cannabis. Do not use double or extra doses.