Dear Doctor: I try not to use opioids for my chronic back pain, but I'm finding myself turning to them more often. Could marijuana help?

Dear Reader: Pain is one of most difficult aspects of medicine to understand. No one can actually feel the pain of another person, but we can see the suffering that it causes. As doctors, we try to alleviate pain in a number of ways.

Opiates -- starting with opium, which is derived from the poppy plant -- have been used for pain relief for more than 3,000 years. The opiates morphine and codeine, also from the poppy plant, were isolated and made available in the early 1800s. Since that time, multiple synthetic opiates such as hydrocodone and oxycodone have been widely used for pain. These drugs attach to opiate receptors in both the brain and spinal cord.

One problem with opiates is that they relieve pain in the short term, but will not control it in the long term. Thus to relieve chronic pain, a person has to perpetually use the medication -- creating one of the addictive aspects of the drugs. The other problem with opiates is that people become tolerant of the medications, meaning that with consistent use, a person needs more medication to relieve the same amount of pain.

For these reasons, opium and its progeny have been abused worldwide. The United States is facing an epidemic of opiate abuse, with prescription opiate medication leading to a rapid increase in lethal drug overdoses. In 2014, more than 18,000 people died from overdosing on prescription opiates, according to the federal Centers for Disease Control and Prevention.

Marijuana has been used also for more than 3,000 years. It works through the endocannabinoid system of the body, which has receptors in the brain and spinal cord as well as the immune system. The receptors in the brain and spinal cord can decrease muscle spasms and pain, while those receptors in the immune system can decrease inflammation and pain.

A 2015 study published in the Journal of the American Medical Association (JAMA) looked at 14 different clinical trials of marijuana use by multiple sclerosis patients and found relief from chronic pain, nerve pain, and pain and muscle spasm. Another study published in 2015 in JAMA looked at 28 different studies with 2,454 patients and found a 30 percent reduction of pain with cannabis-related products compared with placebo.

Opiates can relieve pain in the short term, such as after surgery or an acute injury. But due to their addictive potential and lack of long-term benefit, opiates are not a good choice for long-term pain relief.

Marijuana is not without its own potential risks and side effects. These include short-term memory loss, poor motor coordination, paranoid thoughts and, for some, psychosis. Long-term use can also create the potential for addiction, but not to the degree of opiate medications. Also, overdosing on marijuana doesn't lead to death, as it can with opiates.

My suggestion in regard to chronic back pain is to try other methods of pain control over opioids. These include physical therapy, yoga and stretching. If these don't work, marijuana is an option, but beware of its side effects -- and try to minimize its use.

(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.)

Dear Doctor: I keep reading about new cancer drugs that have been developed in clinical trials. What exactly is a clinical trial and how does it work?

Dear Reader: A clinical trial is a scientific study that looks into whether a specific drug, medical treatment, device or approach is not only effective, but also safe. Although clinical trials for new drugs often get the most press, other important advances arise from the process. New ways to screen for disease, new methods of diagnosis, and techniques that will improve the quality of life for people living with disease are all important advances made in clinical trials.

New therapies are tested in treatment trials. Prevention trials investigate methods of lowering disease risk. In screening trials, optimal methods to discover the onset of disease are tested. Supportive care trials focus on quality of life for patients with debilitating disease. Diagnostic trials focus on tests and procedures to pinpoint the exact type of cancer or condition a patient has.

So how does a clinical trial work?

It starts with an idea. A researcher or doctor or other expert comes up with a "what if?" scenario. For example, what if it's possible to develop a drug to help a patient's own immune system fight cancer?

The next step is extensive laboratory testing. If the idea continues to show promise, research moves into a clinical trial.

A detailed plan, known as a protocol, is created. It states who is eligible to take part in the clinical trial, details all of the tests and procedures that will be performed, names the drugs that will be involved, and describes how the drugs will be administered. The protocol also indicates the length of the clinical trial, and how the information will be collected and collated.

Clinical trials are conducted in four distinct phases that may take place over the course of several years. They begin with Phase 1, which is initial testing on a small group of participants to assess safety and identify side effects. In Phases 2 and 3, the new drug or treatment is given to ever-larger groups of people to further evaluate safety and efficacy. By Phase 4, the drug or treatment has been approved by the FDA and is now evaluated in a large population.

If you're thinking about joining a clinical trial, you should know:

-- The specific purpose of the study;

-- Why researchers believe the experimental therapy will be effective;

-- What drugs, tests or procedures the trial entails;

-- Any risks or potential side effects of the treatment;

-- How much time is required;

-- How your daily life will be affected;

-- How you will know whether the therapy is successful.

It's not an exaggeration to say that clinical trials are at the heart of modern medical advances. Many of the cancer treatments that are saving or extending lives today began as a "what if?" idea in a clinical trial. And while participants may join in hopes of being on the receiving end of a medical advance, they also have the satisfaction of knowing that they are contributing to the body of knowledge that will make medicine even more effective in the future.

(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.)

Dear Doctor: A news report recently said that statins are underused. I'm 50 with normal cholesterol. Should I take one just in case?

Dear Reader: Statins, which are a type of cholesterol-lowering medication, have consistently shown benefit in reducing the risk of heart attacks and strokes in people who have had a previous heart attack or angina. This benefit is called secondary prevention. Statins have also shown benefit in people with risk factors for heart disease who have never had a heart attack; smokers; and people with diabetes, hypertension or a family history of heart disease. This is called primary prevention.

In people like yourself, the potential benefit of statin use is not as clear-cut. So, first, let's look at the Jupiter study, published in 2008. The 17,802 people in this study had normal cholesterol levels -- that is, an LDL score (for low-density lipoprotein, the so-called "bad cholesterol") of less than 130 -- but they had an elevated level of highly sensitive C-reactive protein (CRP), a marker for both inflammation and a heightened risk of coronary artery disease.

Researchers divided participants into two groups, with one group taking a daily placebo and the other group taking a daily 20-milligram dose of rosuvastatin. The study was stopped in less than two years because of the significant benefit seen in the group that took the statin.

The study authors found a 44 percent decrease in deaths from heart attacks and strokes and a 20 percent decrease in the total death rate among the group who took the statin. Not only did participants who took rosuvastatin show a reduction in cholesterol, they also showed a decrease in their levels of highly sensitive CRP. That suggests that statins reduce both cholesterol and the inflammation that may lead to vascular disease.

Now let's look at what to consider if your CRP level is normal and you have normal cholesterol. A 2001 study in the New England Journal of Medicine followed 6,605 men and women in Texas who had either normal CRP levels or abnormal CRP levels. One group was given a statin, called lovastatin, and the other group was given a placebo. Although there was a benefit seen with lovastatin among those who had an elevated CRP level, the benefit was not seen in those who had a normal CRP level.

One conclusion from the data is that if you have normal cholesterol and no other risk factors, you should have your doctor check your levels of highly sensitive CRP. If the CRP is persistently elevated, then there is likely benefit to a cholesterol-lowering medication. One word of caution, however: If you have inflammation related to either infection or an autoimmune condition, the CRP will be elevated because of those conditions and therefore won't be a reliable marker.

Doctors currently assess the need for statins by looking at risk calculators. These risk calculators assess an individual's risk of having a heart attack over the next 10 years. Some doctors recommend that people start statins if their 10-year risk of a heart attack is 7.5 percent. So if you're a healthy 55-year-old man with normal cholesterol and a blood pressure of 125/70, your calculated risk would be 7.83 percent -- and many doctors would recommend a statin. However, the science behind the risk calculator is poor, with a large Kaiser Permanente study of 307,000 people showing that it may significantly overestimate risk.

That finding emphasizes the need for the CRP test. If that test is normal, a statin would be unlikely to provide any benefit to you.

(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.)