A new review of existing research confirms that a weight-loss drug raises blood pressure, posing a risk to obese patients who hope to reduce hypertension by shedding pounds.

Many doctors assume that patients automatically lower their blood pressure when they become thinner, but that is not necessarily the case when they use drugs to lose weight, said review lead author Dr. Andrea Siebenhofer.

In the big picture, “anti-obesity drugs are no wonder pills and should be prescribed only if patients beg doctors for some tablets which help them to lose some weight,” said Siebenhofer, a researcher at the Medical University of Graz in Austria.

The review authors examined research regarding three weight-loss drugs — orlistat, sibutramine and rimonabant. They looked for studies that lasted at least six months and compared patients with high blood pressure who took one of the drugs to those who took a placebo.

The analysis appears in the latest issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

The researchers found no studies that met their criteria for patients who took rimonabant, known by the brand name Acomplia.

The drug is not available in the United States; in 2007, the Food and Drug Administration declined to approve its sale and asked its manufacturer to provide more information about its safety. In 2008, the manufacturer agreed to suspend its sale in Europe, amid reports that it heightened the risk of suicidal thoughts.

The review authors did find four studies examining each of the other two drugs, orlistat and sibutramine.

Orlistat, known by the brand names Xenical and Alli, is both an over-the-counter and a prescription drug in the United States. Sibutramine is a prescription drug sold under the brand name Meridia.

The researchers conducted a meta-analysis by combining the studies and adjusting the statistical results to account for their sizes.

In those treated with orlistat, blood pressure fell by an average of 2.5 mm Hg systolic and 1.9 mm Hg diastolic.

However, the diastolic blood pressure levels of patients who took sibutramine rose by 3.2 mm Hg, according to the meta-analysis.

Systolic blood pressure is the top number in a blood-pressure reading (like 120/80) while diastolic is the bottom number.

The review of sibutramine research had some limitations. The review authors only looked at two of the four studies into the drug because they believed the other two did not meet the criteria they had set for inclusion in the meta-analysis.

In addition, the researchers reported that the two studies they did include failed to provide enough information to allow them to calculate how the drug affected systolic blood pressure.

Carla Wolper, a member of the research faculty at New York Obesity Research Center at St. Luke’s Hospital, said weight-loss drugs have a place in obesity treatment, but that it is important to prescribe them with care and use them in conjunction with other strategies.

A “smart dietician” is crucial to success, Wolper said, as long as he or she “helps people adjust their diet without making a 180-degree change and uses cognitive behavior therapy to challenge people’s ideas” about eating.

Wolper acknowledged working on a drug company-funded study into orlistat.

Dr. Raj Padwal, an assistant professor at the University of Alberta in Canada, said the weight-loss drugs only result in modest amounts of weight loss — typically 6 to 11 pounds — but do improve cardiovascular health. Sibutramine is the exception because it raises blood pressure, he said, and a large study is underway to see if it affects death rates in patients.

Only about 2 percent of patients continue to use the drugs after two years and many find the amount of weight lost disappointing, Padwal said. Side effects are also a problem — orlistat can cause loose stools, for instance — and the drugs are expensive, he added.

“There are no magic pills,” he said. “These pills may help a minority of people, and I’ve seen some people lose a lot of weight, but treatment must be supervised by a health-care provider with appropriate monitoring of parameters, such as blood pressure.”

Siebenhofer A, et al. Long-term effects of weight-reducing drugs in hypertensive patients. Cochrane Database of Systematic Reviews 2009, Issue 3.

Source: Health Behavior News Service