Dear Doctor: How are medical marijuana and CBD oil different from each other? Some states don't allow sale of the former but do allow the latter. I ask because an over-the-counter CBD oil -- which does not contain THC -- stopped my microscopic colitis within two days.

Dear Reader: Marijuana, also known as cannabis, is a leafy plant that grows in many regions of the world. It's best known for producing buds and leaves that contain THC, or tetrahydrocannabinol, the compound that gets you high when smoked or ingested. When people talk about medical marijuana, they're referring to cannabis that, due to state laws, is legally for sale to individuals with a medical recommendation. At this time, medical marijuana is legal in 30 states and in Washington, D.C. At the federal level, however, cannabis is a controlled substance that is illegal.

When it comes to the cannabis plant, the THC that gets you high is just one of about 80 similar chemical compounds found within its resin. Known as cannabinoids, they produce a range of druglike effects within the body. One of those compounds is cannabidiol, or CBD. It is extracted from the buds and leaves of hemp and cannabis plants and, unlike THC, does not have psychoactive properties. It has been shown to be effective in treating certain forms of childhood epilepsy. There is also evidence that it can be helpful for people dealing with anxiety issues. CBD oil has also shown promise in recent studies looking into its effects in cancer treatment, Type 1 diabetes, sleep disorders, Parkinson's disease and seizure disorders.

The challenge with CBD oil is that, since it is technically illegal, there is no federal oversight or regulation for its production. Although it is sold in a variety of forms and a range of concentrations, none of them have been approved by the Food and Drug Administration. At this time, 17 states have laws that address CBD sales and usage, but not all of them oversee production. According to a recent study published in the Journal of the American Medical Association, more than 60 percent of the CBD products available for sale online misstated their concentrations of cannabidiol. Some products contained less CBD than was stated on the label, while others contained more. Some CBD products turned out to contain significant amounts of THC, which means they would cause a user to get high.

For now, the CBD marketplace remains a bit like the Wild West. Many of the claims made by users remain unproven, and potential side effects or ill-effects of its use over time remain largely unknown. The good news is that cannabinoids have shown promise in a number of therapeutic uses and have become the subject of widespread scientific inquiry. Researchers are currently looking into their effect on glaucoma, various cancers including colon cancer, liver and brain function, neuropathic pain and intestinal inflammation, to name just a few. We're at the very beginning of understanding the therapeutic potential of cannabis compounds. We think the future of it will prove fascinating.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: What are the best medications for acid reflux? I've tried doxycycline and metronidazole (Flagyl), for H. pylori infections, which made me sick, as well as Prilosec and Pepto-Bismol.

Dear Reader: That's a question asked by many people in the United States, where gastroesophageal reflux disease (GERD) affects an estimated 20 percent of the population. The condition is less common in other parts of the world, although its worldwide incidence is increasing.

Some degree of reflux normally occurs after eating but is not felt. However, when a significant amount of the stomach's acidic contents rises up to the esophagus, it injures the esophageal tissue -- and causes pain. The thick lining of the stomach can handle the acidity; the esophagus cannot. The burning sensation under the breastbone after eating is what people commonly identify as "heartburn." Some people even feel the regurgitation in the back of their throat and mouth. Chronic irritation of the esophagus can cause abnormal cells to form within the esophageal lining, and sometimes these abnormal cells can develop into esophageal cancer. So, although GERD is common, it should not be taken lightly.

The bacteria for which you were treated, Helicobacter pylori, is associated with inflammation and ulcers of the stomach, but its role in GERD is not definite. Some data show that treating H. pylori with antibiotics such as doxycycline and metronidazole reduces GERD in those who have inflammation in the lower portion of the stomach and duodenum. But for you this doesn't seem to have helped.

My first thought in your case has nothing to do with medications. That's because acid reflux is normally prevented by a sphincter between the stomach and the esophagus -- and there are chemicals in our diets that relax this sphincter, allowing the acidic contents to rise up. These chemicals, found in chocolate, alcohol, caffeine, nicotine and mint, can allow the lower esophageal sphincter to loosen, as can, to a lesser degree, onions and garlic. I would look closely at this short list, focusing on the first five, and, if you have not already done so, eliminate them. If these chemicals are causing greater acid reflux, removing them will help relieve your symptoms.

For some people, acid reflux will persist even with dietary changes. When the reflux is severe and enduring enough to damage the esophagus, treatment is necessary. The best treatment is to decrease the acidity of the material coming up. Antacids like calcium carbonate or aluminum hydroxide can help in the short-term, but they do not provide long-term relief; H2 blockers (Zantac, Pepcid, Tagamet) can. They block the histamine-2 receptor in the stomach and thus decrease acidity. They work well for mild to moderate symptoms that are intermittent. However, if used for more than six weeks, they may start losing their effect.

For persistent or severe symptoms, or for severe esophageal inflammation, a proton pump inhibitor (like the Prilosec you took) is necessary; it can be used for up to eight weeks (and sometimes longer if symptoms persist). In addition to the PPI, an H2 blocker taken at bedtime and possibly during the day can boost the relief. Lastly, there's the muscle relaxant Baclofen. Multiple small studies have found that it decreases the frequency of reflux.

So, in other words, keep trying -- and make sure a doctor keeps an eye on your symptoms and the condition of your esophagus.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Hello, dear readers!

We're on the cusp of summer and that means it's our duty as doctors (and mothers) to remind you to please protect yourselves and your family against the sun as you spend more time outdoors, and against the ticks and mosquitos the season always brings. We've written about this before, but if you have any new questions or need clarifications, please drop us a line.

A column in which we addressed the topic of hackers interfering with the proper workings of wireless medical devices, such as pacemakers, got a lot of response. Many readers found it extremely unsettling, and honestly, we're right there with you. The good news, as we said in the column, is that despite how easy television dramas and films make this type of hacking appear, it's actually quite difficult. But if you're worried enough to want to take preventative measures, a letter from a physician in Spokane, Washington, offers an interesting option. His inspiration comes from the range of RFID-blocking products now available to fend off electronic snoops and pickpockets. In this case, the answer is a special vest.

"The vest is lined with metallic mesh to block potential 'pinging' and the theft of personal information," he wrote of a garment he saw in a travel store. "It occurs to me that these would also block 'Bluetooth' and other RF signals being used to hack an internal medical device. It would be simple for a cardiologist to verify this. Simply obtain a vest, have it in the office and when patients come in for modification of settings on an implanted defibrillator or pacemaker, have them wear the vest first, and see if it blocks the modification."

In response to a column about how noise pollution adversely affects health, a reader from Oklahoma asked us to recommend a set of noise-canceling headphones. Because everyone's needs are so different, we suggest scanning the selections from online retailers, like Best Buy, Amazon, Costco and the like. What we find to be helpful about shopping online for items like these are the many reviews posted by fellow shoppers. They can give you a good sense of what each product can (and can't) do, and often answer detailed questions from fellow shoppers, all of which can help you to find the right device for your specific needs.

We'll wrap up with a question stemming from our column about the measles vaccine. A couple who are headed to Paris this fall (lucky you!) ask whether they should get vaccinated for measles. Because you indicate that you both had measles as children, the answer is no. According to guidelines set by the Centers for Disease Control and Prevention, you are considered to be protected from measles if you have either already had the disease or have already received the appropriate doses of the vaccine. Boosters of the measles vaccine are not needed. If you're not sure whether you're protected, you can find out with a simple blood test.

Thank you again for all of your letters. We hope you have a great summer and look forward to continuing this conversation next time.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)