Dear Doctor: Years ago, I was told not to consume grapefruit or grapefruit juice with statins. Now I understand that this restriction no longer applies. Is this correct?

Dear Reader: The reason people are warned to steer clear of grapefruit when taking statins, which are drugs that lower cholesterol, is that certain compounds within the fruit and its juice affect the way the medications are absorbed. Known as furanocoumarins, they interfere with the metabolic processes that break down a range of medications, including statins. And while you're correct that there are now a few brands of statins that don't interact with those compounds, it's important to check with your pharmacist or physician regarding your particular prescription before adding grapefruit to your diet.

Statins are a class of drugs that get broken down with the help of an enzyme known as CYP3A4, which is found in the gastrointestinal tract and liver. It's a process that controls how much of a drug is released into the bloodstream, and it is factored into the calculations used to determine drug dosages. What happens in the presence of furanocoumarins, which are found not only in grapefruit but also in pomelos and Seville oranges, is the work of that key enzyme is inhibited. As a result, a larger amount of the drug than is intended enters the blood and accumulates in the body. In the case of statins, too much of the drug in the body can lead to grave complications, such as increased risk of damage to the liver and muscles, which can lead to kidney failure.

Grapefruit is a good source of vitamin C and has a bit of potassium as well, so patients often ask if there's a minimum amount they can safely consume while taking statins. Unfortunately, with many statins, the answer is still no. That's because we each secrete a different amount of the CYP3A4 enzyme in the small intestine. The same glass of grapefruit juice that would be safe for one person would be dangerous for someone else.

Interestingly, that same compound that generates an overabundance of statins in the blood will decrease the available amount of a few other drugs, including fexofenadine, an allergy medicine sold under the brand name Allegra. Apple juice and orange juice have the same effect on fexofenadine, which is why the labels on both the prescription-level and over-the-counter varieties of the drug carry a warning against taking it with any fruit juices.

An estimated 20 percent of the population between the ages of 45 and 70 are prescribed statins, so the fact that several of the brands now available do not appear to affect the CYP3A4 enzyme is good news. The statins that remain on the no-grapefruit list are atorvastatin (Lipitor), lovastatin (Mevacor) and simvastatin (Zocor). And while the current literature suggests that rosuvastatin (Crestor) and pravastatin (Pravachol) as well as a few other statin drugs have limited or no interaction with furanocoumarins, we urge you to check with your pharmacist or physician before adding grapefruit to your diet.

(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: After suffering from a metallic taste in my mouth for two years, I've been told by my doctor that I might be suffering from burning mouth syndrome. What can you tell me about this? I'm past menopause, take blood pressure medication, have had numerous X-rays and am pre-diabetic, all of which an internet search suggested might be factors.

Dear Reader: Burning mouth syndrome is a poorly understood chronic condition that leads -- just as the name says -- to a burning sensation within the mouth. The sensation occurs without any visible changes -- no lesions, no redness, just pain. The rate of the disease varies widely, but it appears to occur in about 1 in 1,000 people. The syndrome is rare in people under 30 and is most prevalent in those ages 60 to 80. Women are more afflicted than men by a ratio of 5-to-1.

Multiple theories have been proposed about the syndrome's cause, with a dysfunction of nerves that lead to the mouth being the most likely reason. These nerves fire abnormally, giving the sensation of pain even when there's no trauma to create pain. But then, the brain itself may play a role, possibly altering the sensory input received from the mouth. Also supporting a brain connection is the fact that the syndrome is frequently associated with stressful life events, sleep disorders, anxiety and depression.

Regardless, the pain is described as a scalding sensation, accompanied by tingling, numbness and a feeling of dryness in the mouth. A bitter or metallic taste (like you are experiencing) is noted in two-thirds of patients. The tongue is the most common area involved, but the pain can occur anywhere in the mouth, including the lips.

The syndrome is characterized by how often the symptoms occur. For 10 percent of people, the symptoms occur every few days; 35 percent of people experience the symptoms daily, but find them worse in the evening and reduced or absent in the morning; 55 percent of people have symptoms all day long.

As you have done, it is important to rule out specific causes for the burning sensation in the mouth. Vitamin deficiencies, diabetes, autoimmune conditions and certain types of chemotherapy or radiation can lead to mouth-related nerve damage. Infections, the antidepressant paroxetine and ACE inhibitors used for blood pressure can all cause mouth pain.

Treating the syndrome can be difficult. Topical medications such as capsaicin (from chili peppers), clonazepam, lidocaine and doxepin can deaden the nerve stimuli in the area of pain. In small studies, the antioxidant alpha-lipoic acid has shown benefit in 35 to 70 percent of people with the syndrome when taken at 600 milligrams per day.

Because of the psychological issues often associated with burning mouth syndrome, cognitive behavioral therapy can be effective in reducing pain, as can antidepressants -- SSRIs, SNRIs and tricyclic drugs, like amitriptyline. Drugs used for nerve pain, including gabapentin and pregabalin (Lyrica), may also help.

Unfortunately, burning mouth syndrome can last for months to years, with many people having some degree of symptoms even after five years. So it's best not to simply hope that it will go away. Severe symptoms warrant the use of a topical medication, alpha-lipoic acid, cognitive behavioral therapy or even oral medications.

(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: I read a few years ago that someone wound up with tapeworms after eating raw fish, and now it has apparently happened again. What's the deal?

Dear Reader: Because we're familiar with both of the incidents you're referring to, we think it's a good idea to start by letting any sensitive readers know that we'll be discussing worms and intestines, with details that may be unsettling. OK, ready?

Six years ago, a Japanese man who frequently ate raw salmon became ill with stomach pains and watery diarrhea. According to an account published in the journal BMJ Case Reports, he discovered that a tape-shaped object had emerged from his anus. After infectious disease specialists examined the contents of the man's stool, it was determined that the object, which was close to 40 inches long, was Diphyllobothrium nihonkaiense, commonly known as the Japanese broad or fish tapeworm. (And yes, we had to look up the spelling.)

Earlier this year, during an episode of a medical podcast, an emergency room physician from Fresno, California, described a similar incident. A patient went to the hospital after he pulled a 5-foot-long worm out of his body during an episode of bloody diarrhea. The man then wrapped the worm around a toilet paper roll and headed for the ER, where he presented the worm to the doctor. As with the Japanese man, it turned out that the California man frequently ate raw salmon. In fact, he ate it every day. Although it was impossible to be certain, doctors involved with the case suspected that the raw salmon was the source of the tapeworm infection.

Cases like this are rare, but the truth is that any time you eat raw or undercooked meat, you run the risk of ingesting whatever parasites may have been present in the fish or animal. These range from minute, single-celled organisms that can only be seen with a microscope to the worms whose unnerving size help these stories of infection go viral. In the case of the Japanese broad tapeworm, it had been believed that it was limited to areas of Asia. But according to a report from the Centers for Disease Control and Prevention published last year, it has now been identified in wild salmon caught in Alaska.

Symptoms of infection include the pain and diarrhea that both of the men reported. Diagnosis is made by a microscopic examination of the patient's stool for eggs, or for segments of the tapeworm itself. Although the tapeworms produce and release numerous eggs while in the intestine, it can take several stool samples to find them, according to the CDC. The good news is that a tapeworm infection can be successfully treated with several safe and effective drugs.

So how do you avoid tapeworm infection in the first place? The easiest and most effective way is to never eat raw or undercooked fish. The CDC wants you to cook your fish to an internal temperature of at least 145 degrees. Freezing fish at minus 4 degrees or lower for seven days or at minus 31 or lower until solid will also kill any parasites.

(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.)