Skip to main content
King County logo
Although marijuana use by adults has been made legal in Washington State, that does not mean it is without health risks. The safety of marijuana has not been established. Just like tobacco and alcohol, it has been associated with health and social problems. It is difficult to predict how marijuana will impact any individual because marijuana has not been studied as much as other drugs. Like alcohol – there are individuals who may use marijuana infrequently while others will become regular users and possibly dependent. Read more about marijuana and health in these articles published in the New England Journal of Medicine, the Journal of the American Medical Association and at the National Institute of Drug Abuse website.

Cannabinoids, the active ingredient in marijuana, affect areas throughout the body, but they mostly affect the central nervous system (brain and spinal cord). The main cannabinoid chemical in marijuana that causes intoxication is tetrahydrocannabinol (THC). Another cannabinoid of medical interest is cannabidiol (CBD), which does not cause intoxication.

Marijuana, like all drugs, has potential risks. Regular smoking of marijuana is associated with breathing problems such as cough and increased risk of lung infections. It can also be addicting and can cause problems with thinking, memory and coordination, anxiety, depression, and other behavioral effects that interfere with work, school, and relationships. It causes an increase in heart rate, which may increase the chance of heart attack in people who are already at risk. Marijuana can also cause problems with brain development in adolescents through 25 years of age that can be long-lasting, including possible decline in IQ among adolescent marijuana users.

More common effects of marijuana can include dizziness, dry mouth, disorientation, euphoria, confusion, sedation, nausea, vomiting, muscle spasms and increased appetite.

How marijuana affects health is determined by how it's consumed. Marijuana is most commonly smoked, such as from pipes, bongs, paper-wrapped joints, blunts and other items including devices that heat or vaporize marijuana. It can also be consumed through foods and beverages, such as brownies or tea.

Smoking marijuana can damage the lungs resulting in chronic cough, phlegm production, wheezing, and bronchitis. Smoke from marijuana combustion has been shown to contain many of the same toxins, irritants and carcinogens as tobacco smoke. Marijuana smokers also tend to inhale more deeply and hold their breath longer than cigarette smokers, which leads to greater exposure. Long-term marijuana smoking is not known to be linked to an increased risk for lung cancer.

Secondhand marijuana smoke contains many of the same toxins and carcinogens found in directly inhaled marijuana smoke, in similar amounts if not more. While there is no data on the health consequences of breathing secondhand marijuana smoke, there is concern that it could cause harmful health effects, especially among vulnerable children in the home. Additional research on the health effects of secondhand marijuana smoke is needed.

Smoking marijuana also hurts the lung's first line of defense against infection by killing cells that help remove dust and germs as well as causing more mucus to be formed.

Marijuana smoking also poses a threat to those with weakened immune systems. Aspergillus is a mold that can cause lung disorders and can grow on marijuana, which if then smoked exposes the lungs to this fungus. However, it rarely causes problems in people with healthy immune systems. Marijuana from licensed and regulated retailers in Washington State is inspected to reduce the risk for contamination.

Learn more from the American Lung Association on Marijuana and Lung Health.

Vaporizers are machines that heat the marijuana to release its active ingredients in a mist without smoke. This may reduce respiratory complaints and any specific medical risks associated with inhaling smoke. The potential adverse neurologic, cardiac and behavioral effects of marijuana would still be present when smoked through a vaporizer.
Yes. People should be careful when eating marijuana because of delayed effects. Eating marijuana rather than smoking it avoids the potential health impacts from smoke on the throat and lungs. However, effects from eating marijuana can be delayed. Typically, it takes 30–60 minutes to feel effects from eating marijuana, peaking at approximately 2–3 hours after eating. The effects from eating marijuana last longer than some users prefer. Although the effects are similar to smoked marijuana, the delayed onset of feeling high may make it difficult to control how much one consumes, increasing the risk of taking more than desired. The potential adverse neurologic, cardiac and behavioral effects of marijuana would still be present when it is eaten.

No. Anyone under the age of 21 cannot purchase or use recreational marijuana. Studies suggest that the younger a person starts using marijuana regularly, the more likely they are to become addicted. The teenage brain is still developing, and some studies suggest regular use can cause problems with brain development, memory, learning and attention, school completion, and behavioral problems. Some studies have shown that adolescents who use marijuana regularly are at higher risk of developing depression or schizophrenia. Read more about Adolescents and Marijuana from the University of Washington's Alcohol & Drug Abuse Institute (ADAI).

Public Health is very concerned about preventing youth access to marijuana. King County has proposed to the Liquor Control Board strong advertising, labeling and packaging rules similar to tobacco and alcohol. King County has also requested strong health warnings in educational materials that will be distributed, for these warnings to be posted at the point of sale, and a ban on products that infuse marijuana and alcohol or marijuana and tobacco due to their potential appeal to youth.

No. Just like with alcohol and cigarettes, there is likely no safe amount of marijuana use in pregnancy. If a mother is using marijuana she can pass the active ingredient in marijuana, called THC, to the baby through her placenta before the baby is born and through her breast milk when breast feeding. There are not enough good quality studies to know with certainty how marijuana use affects the developing fetus and breastfeeding baby, but there is cause for concern. Marijuana may cause problems with the development of the baby's brain and nervous system. There are also concerns regarding the effects of marijuana smoke on the mother and baby. Pregnant women or women contemplating pregnancy should discontinue use of marijuana for medicinal purposes in favor of an alternative therapy for which there are better pregnancy-specific safety data.

Additional information about marijuana, pregnancy and breastfeeding is available at ADAI and the American College of Obstetrics and Gynecology.

No. People under the influence of marijuana should not drive or operate complex machinery. Like alcohol, marijuana can interfere with coordination, alertness, and slow a person's response time, putting them and others around them at risk of harm. Read more about Marijuana and Driving at ADAI.

Not always. As with alcohol, marijuana should not be used by people on any medication that decreases one's ability to safely drive or operate complex machinery. Drugs that should not be combined with marijuana include opiate medications and benzodiazepines. People taking medications for alcohol or drug dependency, depression, anxiety, panic or thought disorders should also avoid using marijuana. People taking other prescription medications should talk with their health care provider about the risk of other interactions.

Read more about Marijuana and Prescribed Medications at ADAI.

No. Sometimes referred to as "spice," synthetic marijuana can cause agitation, nausea, vomiting, tachycardia (rapid heartbeat), elevated blood pressure, tremor, seizures, hallucinations, paranoid behavior and coma. It does not contain any of the ingredients found in actual marijuana.

Read more about synthetic marijuana's link to hospital emergency visits at the U.S. Substance Abuse and Mental Health Services Administration.

It is estimated that about one in ten people who use marijuana will become dependent on the drug. The more frequently a person uses the drug, the more likely they are to become dependent. It is not known if marijuana use increases the risk for use of other drugs (i.e. if marijuana is a "gateway drug").

Yes. Marijuana affects the brain's "reward center" in the same way as many other drugs. Some studies have shown that regular marijuana users experience withdrawal symptoms for several weeks after they stop using. Withdrawal symptoms can include anxiety, restlessness, decreased appetite, irritability and trouble sleeping, including having strange dreams.

Although many people use marijuana to treat conditions including pain and nausea caused by HIV/AIDS, cancer, and other conditions, the scientific evidence to date is not sufficient for the marijuana plant to gain FDA approval.

Two synthetic cannabinoids, dronabinol and nabilone, are available in pill form. These drugs are FDA approved and available by prescription. They are used in some patients to treat nausea and vomiting due to chemotherapy. Dronabinol is also used to treat loss of appetite and weight loss in patients with HIV/AIDS or cancer.

Effects may include:

  • a mildly euphoric, relaxing intoxication or "high"
  • impaired coordination; dizziness
  • difficulty with thinking, problem solving, learning and memory
  • distorted perception; anxiety, panic or paranoia
  • decreased motivation
  • increase in heart rate; lowering of blood pressure
  • appetite stimulation; dry mouth

Very rarely marijuana use may lead to acute psychosis involving delusions and hallucinations. Read more about the therapeutic potential of cannabis (PDF, The Lancet)

Call the Washington Recovery Help Line-24 Hours Help for Substance Abuse, Mental Health and Problem Gambling 1-866-789-1511.

16. Pesticides and pot: what marijuana users should know

The passage of I-502 in 2012 means that marijuana is now a legal crop in Washington state. Growers of most of the fruit and vegetables we eat routinely use pesticides and other chemicals to reduce or eliminate crop destruction. Because marijuana is considered illegal by the federal government, the crop stands outside the federal pesticide evaluation and oversight system. The Washington State Liquor and Cannabis Board (LCB) has tried to address this gap by providing growers with a list of pesticides that may be used by marijuana growers, along with an explanation of the criteria used to select the pesticides. These pesticides were selected because their use on marijuana plants would not be in direct conflict with federal law (they are allowed on other food products) and they are considered to pose minimal risk to health when used as directed. Marijuana retailers are required to document all pesticides used on marijuana products that they sell and provide customers and regulators the information on pesticides used upon request.

The potential for pesticides to be present in marijuana is not new and was a concern before the legalization and regulation of medicinal and recreational marijuana products. Pesticides can pose a risk not only to marijuana users but also to workers who use the products and to the environment. We don't know that the problem is worse at this time than before regulation, and given the fact that there are now requirements for growers regarding acceptable pesticide use in marijuana sold by regulated stores (and soon to include "medicinal marijuana" sold at regulated stores) the risk may be lower at this time than in the past.

Concerns about unapproved pesticide use

But in Colorado and elsewhere, pesticides that were not approved for use on marijuana have been reported in product from recreational stores. Could this happen in Washington? The Washington State Liquor and Cannabis Board (LCB) has licensing, regulatory and enforcement authority over recreational cannabis growers, processors and retailers. The LCB inspects each licensed facility prior to licensure to ensure growers have only the approved pesticides on hand. Washington law does not require pesticide testing currently, and at this time there is no routine testing or screening of marijuana products for pesticide residues. However, pesticide testing may be performed as part of a complaint investigation by the LCB. Consumers should know that pesticides have also been detected in medical marijuana and that currently, medical dispensaries in WA have no regulatory oversight by the LCB or any other government agency. However, beginning in July, 2016, sale of all marijuana products will be regulated by LCB and subject to "quality assurance" rules established by Washington Department of Health.

New testing guidelines are coming

At Public Health – Seattle & King County, while we are not the regulatory authority over the marijuana industry, we recognize the need for testing of marijuana products for pesticides and other impurities by certified laboratories and under the authority and direction of the LCB.

Laboratory testing for pesticides in marijuana is complicated, costly and requires special expertise and equipment. Because no pesticides have Federal approval for use in marijuana, there are no levels of pesticides that are considered safe or acceptable in marijuana. This is especially true for pesticides on marijuana that is smoked, because very little is known about the human health effects of pesticide exposure when inhaled. For ingested pesticides, it may be possible to refer to existing Federal guidance for acceptable limits (tolerance) in other food crops for which the pesticide is approved. For pesticides not approved for use in Washington, no detectable amount is acceptable.

The Washington State Department of Health is currently formulating quality assurance standards for marijuana products, including guidelines for pesticide testing. These standards will initially apply to certain products sold in licensed stores and later will include all products. The State is also planning to certify laboratories to test marijuana using standard procedures, but none are currently certified. In addition, because there are so many pesticides, only a sample can be tested for at one time. On September 6, 2015, the Department of Health issued emergency rules regarding marijuana product compliance.Read the explanation and the new rule.

Know the possible risks

Marijuana users should be aware of the health risks associated with marijuana use and the uncertainty regarding the health effects of pesticides that may be in marijuana products.

Reported adverse health effects of marijuana include the neurologic, behavioral, cardiovascular and pulmonary (lung) systems. There have been no cases of human illness identified due to pesticides in marijuana however, the health effects of inhaled or ingested pesticides on marijuana and marijuana products are uncertain because of a lack of research in this area. Therefore, marijuana users should know that in addition to the known health risks of marijuana, it is possible that pesticide exposure through marijuana use could result in health problems. Because marijuana is often smoked or vaped and little is known about the effects of inhaled pesticides, it is important to lean more about the health effects of pesticide exposure both through inhalation (smoking) as well as through ingestion of marijuana products. Marijuana concentrates could contain higher levels of pesticides and impurities than leaf product.

What marijuana consumers and the public can do

Avoid smoking or ingesting marijuana if you are concerned about pesticide exposure. All consumers should ask your marijuana retailer for documentation about the pesticides used on marijuana you purchase.

If you experience any concerning symptoms or unintended health effects after using marijuana, call the Washington Poison Center at 1-800-222-1222. Specialists are available 24/7 and offer free, non-judgmental, and confidential medical advice and can answer your questions related to pesticides and pesticide exposures.

Provide input to Washington State about marijuana-related rule making by checking the LCB website and the Washington Department of Health website.

This section on Pesticides and Pot also available in PDF format.