Dear Doctor: We heard there's a new study that says cannabis changes a teenager's brain. My wife and I suspect that at least one of our 16-year-old son's friends is getting high, and we worry about our son as well. Why isn't there more research about the health effects of cannabis?

Dear Reader: Although a growing number of states are easing restrictions on cannabis, at this time it remains illegal under federal law. According to the Controlled Substances Act, cannabis is a Schedule l drug, along with heroin, LSD, methaqualone (Qualuude) and others. Drugs in this category are considered to have no accepted medical use and a high potential for abuse. As a result of its Schedule l status, studies about cannabis require a special license, which makes scientific research quite challenging.

A couple of years ago, the National Academies of Sciences, Engineering and Medicine published an analysis of cannabis studies completed over the last 20 years. The committee found evidence to support the use of cannabis to treat chronic pain and muscle spasms in people with multiple sclerosis, and to ease nausea and vomiting due to illness or chemotherapy. Among the risks of cannabis was an increase in traffic accidents when driving while high and a spike in accidental ingestion by young children in states where cannabis is legal.

The committee said it found evidence that cannabis use does not give rise to the same cancers that tobacco products do, but that respiratory function can suffer among cannabis smokers. Learning, memory and attention were found to be impaired after immediate cannabis use. Among the body's conclusions was a pressing need for regulatory changes to remove the numerous barriers to rigorous cannabis research.

When it comes to the study you're asking about, which was published in January in the Journal of Neuroscience, scientists at the University of Vermont reported that cannabis use affects the structure of the teenage brain. This held true even in teens who had used only small amounts of the drug a few times.

Specifically, researchers saw an increase in gray matter volume in the amygdala when compared to scans of brains of teens who had never used cannabis. The amygdala is the part of the brain involved in fear and other emotions. Changes to brain structure among the cannabis users were also noticed in the hippocampus, the part of the brain that plays a major role in learning and memory.

What these brain changes actually mean to the future development of the teens is not yet known. However, according to the analysis we discussed earlier, experimentation with substances of abuse, including cannabis, most often begins in adolescence and young adulthood. The committee also found evidence that starting to use cannabis at a younger age is linked to ongoing use that may become problematic.

A survey completed in 2017 found that 15 percent of kids between the ages of 12 and 17 are using cannabis. If you're worried that your son is among them, we think the best thing you can do is talk with him. Share the research, explain your concerns, and let your son know you want this to be the start of an ongoing dialogue.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: After the new year, I started making some serious lifestyle changes, including losing weight and quitting smoking. It's not my first time around, so I hope you have advice to stay motivated. I really don't want to be making these same resolutions next year.

Dear Reader: As we've all learned by now, there's a world of difference between knowing what's best for us and actually doing it in real life. One of the reasons making changes can be so challenging is that even a seemingly simple goal involves altering our behavior -- and our thinking -- on multiple fronts.

Before you begin, we think it's important to fully understand your goals. Let's begin with your resolution to quit smoking. Start with understanding why you're going to make this change. If the answer is for better health, go a bit deeper and make a list of all the ways that smoking makes you feel bad. Are you short of breath? Is it hard to run (or even quickly walk) a short distance? Do you get winded going up a flight of stairs? Maybe you start the day coughing? On the social side of things, perhaps you're sensitive to how your clothes or hair or car smell, how your family and friends respond to your being a smoker, or to the financial cost of your habit.

Once you've written your list -- and we urge you to be as complete, detailed and honest as possible -- you've taken a significant step toward understanding what's at stake as you go about making this change. Where before all you had was the command "quit smoking," you now have a multifaceted understanding of the different ways this habit affects your life. You have imbued your goal to quit with depth and personal meaning. That's important because when you're struggling through the inevitable rough patches that we all go through when making a lifestyle change, you now have multiple toeholds to help stop the fall.

Another element of successful change is setting reasonable interim goals. Sure, the endpoint is zero cigarettes. But two or three fewer cigarettes per day or week, depending on your habit, is definitely a success. The same goes for weight loss. Lose just 5 ounces per week and by the time the next New Year's Eve rolls around, you're down 16-plus pounds. Taking the long view in reaching your goals will make it easier (and far less painful) to integrate ongoing changes into your daily life.

A final note: In your letter you refer to "some" serious lifestyle changes, indicating you've set more than just the goals of quitting smoking and weight loss. If so, you've added a significant level of difficulty. We think it would be wise to prioritize those changes and work toward them sequentially rather than all at once. Pick the goal that's most important. When you feel solidly on the road to success with it, then tackle the next one. That way you've got a better chance of crossing at least one or two of the goals off your list of resolutions, rather than feeling overwhelmed and giving up on all of them.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My mother-in-law just turned 70. Physically, she's great, but when it comes to memory stuff, like remembering new names or shopping without a grocery list, she's not doing so hot. Do you have any mental tricks or exercises to help her? Her doctor says it's all normal and there's no sign of dementia, but my wife is still worried.

Dear Reader: Whether it's forgetting the name of a new acquaintance, where we left our sunglasses or whether we unplugged the coffee pot before leaving the house, we've all had our memory fail us. We agree with your mother-in-law's doctor that some degree of memory loss is indeed a normal part of aging. The volume of the brain, after peaking in our early 20s, then begins a gradual decline. Nerve cells in the brain begin to shrink or even atrophy, and interconnections between neurons become less numerous. Add in the changes to blood flow that occur as the cardiovascular system goes through its own aging process, and occasional struggles with memory come as no surprise.

Memory changes often begin with subtle episodes when you're in your 40s and progress from there. Although these changes have been a recognized part of aging for thousands of years -- the Greeks wrote about it in 700 B.C. -- the fear of dementia can turn each new lapse into an occasion for worry. It's understandable that, despite a doctor's reassurances, your wife and her mother are concerned.

The good news is that her doctor is monitoring your mother-in-law's symptoms and sees no cause for alarm. However, cognitive changes are often gradual. We think it's wise to remain aware of your mother-in-law's mental state.

In the meantime, there has been some interesting new research into improving memory for people of all ages.

According to a study published a few years ago in The Quarterly Journal of Experimental Psychology, a powerful tool in the memory arsenal turns out to be drawing. Researchers asked participants in the study to remember a certain word. One group was asked to write the word down, the other to draw it. When it came time to remember the word, the group that made drawings was markedly better at recall than those who simply wrote the word down. What's really interesting is the drawing technique boosted memory not only of specific words and objects, but also of complex ideas and abstract concepts.

When it comes to remembering names, memory experts advise saying the name aloud as you meet the new person. More recent research found that you boost the memory effect if you use the name of a new acquaintance in conversation moments after you meet. That is, saying the name aloud to a third party helps you to remember it.

Finally, we've known for some time that exercise can help memory. Now a recent study in Nature Medicine suggests irisin, a hormone produced during exercise, is part of the reason. Irisin appears to not only improve brain health, but researchers say it may also lessen the damage that occurs during Alzheimer's disease.

Try sharing these facts and techniques with your mother-in-law. You may also find them to be useful in your own life.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)