On Wednesday, Colorado became the first state to allow legal sales of marijuana for recreational use. Washington state will do the same later this year, and other states might follow suit. Here are answers to some basic questions about marijuana, its effects on the body and the interesting issues raised by legalization:

How does marijuana work?
A greenish-gray mixture of leaves, stems, seeds and flowers of the cannabis plant, marijuana’s main active ingredient is delta-9-tetrahydrocannabinol, or THC. It binds to the surface of nerve cells in high-density areas of the brain involved in feelings of pleasure, memory, thinking, concentration, coordination and movement, and sensory and time perception. THC stimulates this communication network, resulting in a marijuana “high.”
What are its medicinal uses?
About 20 states and the District of Columbia allow the use of marijuana for medical purposes. Most patients are seeking the drug for controlling pain for medical issues including cancer, nervous system diseases, glaucoma and migraines. It is also being used to treat nausea and improve appetites for people with HIV or other chronic illnesses.
What’s the difference between smoking marijuana or consuming it in food, powders or liquid extracts?
When the leaves are smoked, THC moves almost immediately from the lungs to the bloodstream and to the brain. The effects can last one to three hours. If it’s eaten, say in brownies or cookies, it can take 30 minutes to an hour to have an effect, but the high can last up to four hours.
What are the health effects of marijuana use?
In the short-term, it can lead to a rapid heart rate, increased blood pressure, red eyes, dry mouth, increased appetite and slowed reaction time. Long-term use has been linked to impaired thinking, memory problems, panic attacks and other psychological issues. There have also been studies about showing a weakened immune system and, for those who smoke the drug, impaired lung function.
How much marijuana is safe to use? Can you overdose from marijuana?
There are no recorded cases of someone dying from an overdose of marijuana, but it has been a factor in accidents or medical issues that can lead to death.
The concentration THC in seized samples of illegal marijuana has been increasing over the past 30 years, with the average potency more than doubling since 1998, leading to concern about the consequences on young users. But scientists don’t know much about the effects of higher concentration on the body and brain.
Is it addictive?
Yes, it can be. Long-term use, especially by those who start at a young age, has been shown to lead to addiction, with an estimated one out of 11 people who use it becoming dependent on it. Marijuana was responsible for 4.5 million of the 7.1 million Americans dependent on or abusing illicit drugs, according to the 2010 National Survey on Drug Use and Health published by the Department of Health and Human Services. Withdrawal symptoms are similar to those of withdrawal from smoking and include irritability, sleep difficulties and anxiety.
How does marijuana use affect the young?
Nora Volkow, director of the National Institute on Drug Abuse, lamented recently on “The Diane Rehm Show” that legalization of marijuana in some states could make it easier for kids to access the drug. That’s a serious problem, she said, in part because science has shown marijuana can have more profound effects in the brains of young people.
“When you smoke marijuana, you cannot memorize or learn as you should. And if you are at high school and you need to be educating yourself, that’s going to put you at higher risk for actually doing poorly at school,” Volkow said. “The other issue is that, the younger you start smoking marijuana, the higher the risk not only to becoming addicted to marijuana, but it also appears to increase the risk for addiction of other drugs in adulthood.”
Volkow added: “What we know about the marijuana, as well as other drugs, is that the effects of drugs in the human brain are not the same when you take them as a child, adolescent or as an adult, and this is because there are significant changes in the brain as we go in the transition from childhood into adulthood. And our brain continues to change even as adults, but the largest amount of changes really are occurring during those developmental stages, which, of course, leads the brain to function in different ways and respond to stimuli, including drugs in different ways.”
Volkow’s comments are based on mounting evidence. Last year, for example, Canadian and American researchers reviewed more than 120 studies examining cannabis and its effects on the teenage brain. They found strong indications that early marijuana use can alter development and contribute to mental health problems later in life.
“For me, the question is not about whether cannabis is good or bad, but who is more likely to suffer from problems in cannabis, because we know for most people that will not happen,” Didier Jutras-Aswad one of the study’s authors and a University of Montreal neuroscience professor, told the Canadian Broadcasting Corp.
How does marijuana use affect driving?
One of the key questions Colorado lawmakers had to wrestle with in setting up a legal marijuana market: When is someone too stoned to drive? The answer isn’t so simple.
Prosecutors and some state lawmakers have long pushed for strict blood-level limits for THC, the key ingredient in cannabis. Many marijuana advocates argue that the drug affects people differently, and that setting a hard limit could lead to wrongful DUI convictions. They also argue that, unlike with alcohol, traces of the drug remain in the bloodstream long after an individual has smoked pot. Officials in favor of blood-level limits say tests exist that can pinpoint “active” THC in the bloodstream in the hours immediately after marijuana usage.
Studies have shown that smoking marijuana tends to affect spatial perceptions. Drivers might swerve or follow other cars too closely. They can lose concentration and have slower reaction times. Such findings have led some researchers to conclude that driving high greatly increases the chances for an accident, and that smoking pot and drinking before driving is a particularly dangerous mix.
Every state forbids driving under the influence. But convictions in drugged-driving cases generally rely on the observations and testimony of police officers rather than blood tests. The White House in a drug policy paper last year called on states to adopt blood-limit laws in an effort to reduce drugged-driving, but states continue to take different approaches.
Last year, Colorado lawmakers approved a bill that creates a “permissive inference” that someone with a certain level of THC in their blood is impaired. Drivers suspected of driving high generally would have to consent to have their blood drawn, and they could lose their license if they refuse.
Can you use marijuana if you’re pregnant?
A number of studies have shown that babies born to some women who regularly used marijuana suffered from an increased risk of cognitive and attention deficits, memory and learning issues, low birth weight, pre-term delivery and other issues. But more research is needed to figure out to what extent environmental factors played a role in these studies.