Great question, and a hard one. We don’t fully understand yet why this is so. We know that genes play a part, because an inclination for addiction can run in families, and because different strains of mice, rats, and other animals differ in how readily they develop addiction-like behaviors after they’re exposed to drugs. We also know that a person’s environment plays a part in addiction. For example, what are the factors that encourage someone who has tried a drug to keep on taking it to the point where they can’t stop? Many scientists are trying to untangle the answers so that we can find better ways to prevent and treat addiction. See these videos on how anyone can become addicted, and why drugs are so hard to quit.

There are several reasons why people experience hangovers from drinking. One component is dehydration. Alcohol causes the body to get rid of too much fluid, and the dehydration that results can cause headaches, nausea, thirst, and other symptoms of hangovers. While some people think that alcohol helps a person sleep, it actually disrupts sleep, and that can contribute to the grogginess that accompanies hangovers. 

Different drugs act on the brain in different ways, but they all cause release of the neurotransmitter dopamine in the brain’s reward area, which is what causes the pleasurable sensation (the high). Once a person uses a drug repeatedly, their brain starts to adjust to these surges of dopamine; the brain cells (neurons) make fewer dopamine receptors, or they simply produce less dopamine. The result is a lower amount of “dopamine signaling” in the reward area—it’s like “turning down the volume” on the reward signal. Then the person may start to find natural “rewards”—like food, relationships, or sex—less pleasurable; that’s one of the signs of addiction. Also, reduced dopamine signaling in the brain’s prefrontal cortex, which governs our ability to inhibit (slow down or stop) our impulses, makes it harder to resist the urge to take drugs even if a person would like to quit. Learn more about how drugs affect your brain and body

The “gateway drug” concept—where using one drug leads a person to use other drugs— generates a lot of controversy. Researchers haven’t found a definite answer yet, but as of today the research does suggest that, while most people who smoke marijuana do not go on to use other drugs, most teens who do use other illegal drugs try marijuana first. For example, the risk of using cocaine is much greater for those who have tried marijuana than for those who have never tried it. However, this risk is also greater for people who have used alcohol and tobacco. Animal studies suggest that because the teen brain is still developing, using marijuana, alcohol, or tobacco in your teen years (or earlier) may alter your brain’s reward system (see the answer to #3 above), and that may put teens at higher risk of using other drugs. In addition, using marijuana puts children and teens in contact with people who use and sell other drugs, increasing the risk of additional drug use.

The marijuana plant has not been approved by the FDA for the treatment of any medical condition. A pill form of THC (the main chemical in marijuana that affects the brain) is already available for certain conditions, such as nausea associated with cancer chemotherapy and weight loss in patients with AIDS. Early research suggests that some of the active ingredients in marijuana, like THC and cannabidiol (CBD), might be able to help treat conditions and diseases like epilepsy, cancer, or addiction. Scientists are studying THC and CBD to try to develop new medications. However, smoked marijuana is unlikely to be an ideal medication because of its negative health effects, including the risk of addiction and the damage that smoking can do to your lungs.

Yes. Chemicals can have different effects in different animals—for instance, chocolate is delicious to humans and poisonous to dogs—so even small amounts of a drug could be very harmful for your pet. Alcohol can cause a dog to suffer dangerous drops in blood pressure, blood sugar, and body temperature, to have seizures, and to stop breathing. In dogs and cats poisoned by marijuana, signs may be seen within 3 hours, such as a lack of energy, low heart rate, low blood pressure, respiratory depression, hyperactivity, seizures, vomiting, and coma. Also, your pet wouldn’t understand that it had been given a drug, and the sensations that might feel like a “high” to a human would be a very scary experience for an animal.

One of the best things you can do for a friend with a serious drug problem is let them know you are there to support them. Tell them you’re concerned about their drug use and encourage them to seek help from a trusted adult; maybe a teacher, coach, parent, or counselor can help. You can also help by being a strong positive influence; help them get involved in non-drug-using activities like joining a club, playing music, or playing a sport. However, if your friend is becoming a negative influence in your life, you might have to step away from the friendship for a while. If you feel your friend is a danger to himself or herself, or to others, it is important to tell a trusted adult right away; it could save your friend’s life. See NIDA’s “Step by Step Guide” for teens and young adults.

No, they aren’t more addictive—for example, they don’t cause painful physical withdrawal when you stop. Technically, video games wouldn’t be considered addictive. But they do act on some of the same systems in the brain as addictive drugs. For instance, they produce bursts of dopamine (described in answer #3 above), and some people think that playing video games a lot might cause problems similar to drug use, such as being unable to get satisfaction from other things in life.