However, it is important to seek out a physician who is board-certified in obesity medicine
who can help select the appropriate drug based on your medical history. Only a professional can responsibly help you manage the risks and benefits of different drugs, according to Sue Cummings, a registered dietitian who was clinical programs coordinator at the Massachusetts General Hospital Weight Center for the past 20 years.
Weight loss medications are typically indicated for those with a body mass index
(BMI) of 30 or higher, or a BMI of 27 or higher with health conditions such as high blood pressure or type 2 diabetes. A person who is 5 feet 8 inches tall and weighs 200 pounds has a BMI of 30.4; online tools can help you calculate your BMI.
Though there are exceptions, "in general, that's where we start treating people," said Dr. Louis Aronne, director of the Comprehensive Weight Control Center at Weill Cornell Medicine and NewYork-Presbyterian. Drugs are typically prescribed along with diet and physical activity changes.
Since there is a broad range of medications available, finding one that will work is almost always possible, according to Aronne, who co-authored the Endocrine Society's clinical practice guidelines for the pharmacological management of obesity.
Identifying the right match is key, as a drug may or may not be appropriate for someone depending on their health history. For example, if someone has uncontrolled high blood pressure, you wouldn't prescribe phentermine (a weight loss drug approved for short-term use), Aronne explained.
FDA-approved weight loss drugs
In order for a weight loss drug to be approved for long-term use, it must have two years of data showing that it is safe and it works.
In general, a medication can be considered effective for weight management if, after one year of treatment, at least 35% of those in the drug group (and about double the proportion of people of the placebo group) lose at least 5% of their weight.
Weight loss drugs approved for long-term use include orlistat (brand name Xenical), lorcaserin (Belviq) and liraglutide (Saxenda) as well as the combination drugs naltrexone-bupropion (Contrave) and phentermine-topiramate (Qsymia).
In one recent study, these drugs helped overweight or obese people lose at least 5% of their body weight
at the end of a year -- that's at least 10 pounds if you weigh 200 -- compared with a placebo. Qsymia and Saxenda were associated with the highest odds of achieving that amount of weight loss.
Losing 5% to 10% of your body weight is associated with improved blood pressure, triglycerides and blood sugar, factors that lower the risk for heart disease and diabetes.
"A lot of people will say, 'Wow, 5% of body weight, that doesn't sound like a lot of weight loss,' but an average weight loss of 5% reduces your risk of developing diabetes by 50%. That sounds much better now, doesn't it?" asked Aronne, who disclosed relationships involving research, funding and advising with some of the approved obesity drug companies and companies that make weight loss devices (i.e. the balloon EndoBarrier).
Some medicines are prescribed "off-label," that is, for a use other than what it was approved for. For example, metformin is a drug that is FDA-approved for diabetes, but there is evidence that it can produce weight loss even in people without diabetes.
How they work
All of the FDA-approved weight loss drugs except Xenical work on hypothalamic pathways, resulting in decreased appetite and increased feelings of fullness after eating, Aronne said. (Xenical inhibits the absorption of fats by blocking the enzymes that break down fat.)
In essence, when too many calories come in too quickly, this damages nerves in the brain that receive hormonal signals from the stomach, intestine and fat cells that tell the brain how much you've eaten and how much fat is stored. The nerves then become resistant to the hormonal signals, Aronne explained. Medications essentially mimic more food coming in and stimulate more nerves, which gives more of a signal to your brain.
"People say, 'I know why he's fat; he just ate too much' ... but the part that's been left out is that there is a physical change in these nerve pathways that makes it hard to go back. While eating less does temporarily treat obesity, it doesn't change the body's physiology. And that's where medication comes in."
Aronne compares it to smoking and lung cancer. "If somebody smoked their whole life and they developed lung cancer, you would probably tell the person to stop smoking -- but do we expect stopping smoking to be a treatment for lung cancer?"
Factors to consider
Weight loss drugs are not for everyone. Reasons doctors may not prescribe them include pregnancy and breastfeeding as well as any acute serious medical conditions, such as a recent heart attack, stroke or kidney failure, Aronne explained.
There are other factors doctors are looking for as well. Before starting medication, it's best when weight has been stable for some time.
"We often introduce (medication) when one is 'stuck' at a stable weight and is not gaining or losing," Cummings said. Hitting a weight loss plateau, for example -- something common among dieters who have lost some weight, when their metabolism drops to accommodate a smaller body size -- might warrant the help of a drug in order to break through the plateau.
A drug should be continued only if a weight loss of at least 5% of body weight is achieved after three months. If that's not the case, or if there are any safety or tolerability issues -- for example, if someone's blood pressure goes up when taking the drug phentermine -- it's probably time to try a different drug.
"There are a number of options. ... No medicine is right for everybody," Aronne said. "And the process right now is ... trial and error, in order to minimize side effects and maximize effectiveness in any given person."
Sometimes, a combination of medications will be necessary in order to achieve results. "That's where the obesity medicine specialist can really help the patient work through this to get the right medicine for them," Cummings said.
Experts say you shouldn't count on going off of a weight loss drug that has worked for you -- that is, as long as you want to continue to maintain your weight loss.
"People say, 'Give me the meds, and when I lose the weight, I can go off it,' but it doesn't work that way," Cummings said.
"I don't tell people it's forever, but it's long-term," Aronne agreed.
Taking a weight loss drug doesn't guarantee results. "We're not entirely sure why some people don't respond to medications," Aronne said.
If you have tried different weight loss medications and ruled out other possible reasons for lack of weight loss, including lifestyle habits and other prescriptions that cause weight gain, bariatric surgery
might be an option for you.