Weight loss pills, also called diet pills, are nothing new. But their history isn't just long, it's complicated.

Safety has previously been an issue. The FDA stepped in to ban or withdraw several early iterations, some of which were seriously unsafe.

As a result, the agency imposed guidance to ensure more rigorous testing and review of weight loss medications in the late 1990s. This reduced concerns over safety, but the effectiveness of these pills left much to be desired.

"The main problem was that these medications only helped people lose about 4% to 5% of their body weight, some even less than that," says Dr. Nabil Tariq, weight loss surgeon at Houston Methodist. "Patients, of course, weren't too impressed with that."

Weight loss supplements made the story even murkier, growing into a 2-billion-dollar industry as people searched for alternative ways to lose weight. Plenty of products, from "natural fat burners" to water pills, are touted to help, but their effectiveness and safety aren't regulated by the FDA.

Over the last few years, a new generation of prescription weight loss pills has become available, sparking a resurgence of interest in such options.

"The current crop of medications are certainly more helpful than the previous ones," adds Dr. Tariq. "Having said that, the expectations have to be realistic."

Dr. Tariq answers six common questions about today's weight loss medications — from how they work to what people should (and shouldn't) expect.

Do weight loss pills actually work?

Given their convoluted history, it's not surprising that people question whether the weight loss pills available today are effective.

The renewed interest in these drugs stems from results seen with a certain class of type 2 diabetes medications called GLP-1 agonists.

"These drugs have been used to treat diabetes for many years when, through long-term studies, we realized that they also helped with weight loss," says Dr. Tariq. "As a result, some are now approved for weight loss alone in non-diabetics."

The results can be significant. Some of the medications lead to weight loss of 10%-15%, enough to help improve health conditions like diabetes and high blood pressure. One of the drugs, tirzepatide, has been show to reduce weight as much as 20% in some individuals.

"Weight loss medications can be an important — some would even say essential — part of losing a significant amount of weight in the current era," says Dr. Tariq. "But it's important to understand that these medications go hand in hand with dietary changes and activity modification."

Some people think, 'I'm going to take this medication and lose 80 pounds.' To such thinking, Dr. Tariq says, "No, unfortunately, that's not the case yet."

The bottom line: The newer era of weight loss pills are effective, but only if a person is committed to making the other changes necessary to lose weight and keep it off — eating a healthier diet and becoming more active.

How do weight loss pills work?

There are several different weight loss medications — some pills, some injections — and each works in a slightly different manner. Most, though, reduce a person's appetite, notes Dr. Tariq.

"The exact mechanism by which these drugs affect appetite isn't totally clear because appetite itself is so complex," says Dr. Tariq. "It's influenced by a person's blood sugar, gut physiology, mood, stress levels and more."

He adds that if appetite was controlled by one distinct input, a successful anti-obesity drug would have been identified a while ago.

"A few don't affect appetite," adds Dr. Tariq. "For instance, orlistat works by decreasing the absorption of fat. And the newest weight loss medication, tirzepatide, actually affects both appetite and satiety."

The two may sound one and the same, but appetite and satiety are distinct. Appetite is more about how much food a person eats to feel full. Satiety is how long a person feels full after eating.

Are there any side effects to taking weight loss pills?

Previous generations of anti-obesity medications were riddled with adverse effects, but those associated with the new drugs have been fairly limited and much less concerning. (Patients not tolerating a side effect should talk to their doctor.)

"GI issues are the most common complications noticed — bloating and diarrhea, as well as some nausea and cramping," says Dr. Tariq.

Some medications may have other side effects. For instance, options that work by limiting fat absorption can potentially cause fecal incontinence in certain people, while others may cause pancreatitis.

For this reason, your doctor will take your health history into account when determining which weight loss pill is best for you.

When should someone consider taking weight loss pills?

Dr. Tariq stresses that weight loss injections and medications are only right for people who are committed to using them as an adjunct to healthy lifestyle changes.

"These medications alone will not shed the weight," says Dr. Tariq. "So first and foremost, a person needs to be mentally there and not have unrealistic expectations."

Then it's time to talk about what's classified as overweight.

"There are complex debates about how we define obesity, but one imperfect method we currently use is BMI, or body mass index," explains Dr. Tariq. "It's your weight in relation to your height."

A BMI above 30 is typically considered obesity.

"If a person has a BMI of 30 or higher, weight loss medications certainly become a consideration," says Dr. Tariq. "But there are times when a person with a BMI lower than 30 might be a good candidate, too."

For instance, a person with a BMI of 28 who carries most of the excess weight around their waistline (termed central obesity) and also has diabetes is a good candidate for weight loss pills.

"One of the challenges of using these medications more broadly than this is that a lot of the newer ones — the ones getting the ones most attention for how effective they are — are only approved for people with diabetes right now," says Dr. Tariq. "There are non-diabetic people who may otherwise be good candidates, but they would have to pay out of pocket for certain weight loss medications."

Lastly, people with very high BMIs — above 40, 50 or 60 — can also benefit from anti-obesity medications, but Dr. Tariq points out that they may be of benefit after weight loss surgery to help ensure success.

"The weight loss that occurs from taking medications may not be enough for people above a certain BMI," explains Dr. Tariq. "In these cases, weight loss surgery is still the most effective option for losing a significant amount of weight."

Is there a best weight loss pill?

Which weight loss pill is best? It depends.

"It's similar to how we talk about blood pressure medications," says Dr. Tariq. "Which anti-obesity drug is best depends on the person's age, degree of obesity, whether or not they're diabetic, if there's a history of smoking dependence and other factors."

Having said that, he adds that a weight loss injection, tirzepatide, approved last year, is the strongest option currently available.

"It can lead to body weight loss in the range of 15% to 20%," explains Dr. Tariq. "This is the first drug that comes anywhere close to being as effective as surgical weight loss, which typically has the potential to lead to 30% body weight loss."

Can you ever stop taking a weight loss pill?

"As clinicians, we think of obesity as a chronic disease," says Dr. Tariq. "So, for many people, weight loss medications need to be taken long-term."

Does that mean for the rest of a person's life? Possibly, says Dr. Tariq. But with enough success over the course of a year or two — and if good habits are built during that time — individuals may be able to continue their weight loss and maintenance without weight loss pills, Dr. Tariq adds.

What weight loss pills shouldn't be used as is a short-term solution to weight loss.

"Taking weight loss medication is not a seven- or eight-week thing," says Dr. Tariq. "Like blood pressure drugs, people will typically need to take them continuously for quite some time."