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You can't escape the ads. They pop up on TV, on your Twitter feed, on your Facebook page: "100 percent natural." "This miracle pill can burn fat fast." 

The ingredients are seemingly plant-based—green tea extract, bitter orange, raspberry ketones—and harmless-­sounding. Some of these products have been widely touted as safe or downright miraculous. Even Mehmet Oz, M.D., the trusted Dr. Oz, has made headlines because he's featured controversial ingredients on his show. In June he was called to testify at a Senate hearing, where he faced tough questions from Senator Claire McCaskill (D–Mo.). Women who would never dream of taking an old-school chemical diet pill may wonder: Are natural products a safe, easy answer to losing those extra pounds?

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That's what Kari Skitka was hoping. The 24-year-old marketing associate, based in New York City, thought she'd found the answer in a bottle of raspberry ketone pills.

"I'd read they would suppress my appetite and give my workouts an extra boost," she said.

Skitka did lose some weight on the pills, but it came at a price.

"I felt a little manic," she said, "dizzy, shaky and nauseated. But I thought I could handle it. I was willing to endure some negative side effects because I knew I wouldn't be taking it forever. I was looking at it as a short-term solution." 

While dieting, exercising and taking the pills, she lost 20 pounds. But she finally decided the symptoms weren't worth it. She stopped taking the pills, the side effects went away, and eventually she gained back every pound. Still, she was relatively lucky: Other women who have taken these and other seemingly natural weight loss supplements have experienced side effects ranging from mild to extreme—some even life-threatening.

It may seem hard to believe, but dietary supplement manufacturers (unlike pharmaceutical companies) don't have to prove that their products work or even that they're safe. They don't have to get approval from the FDA before selling them to the public. In 1994, Congress passed a law called the Dietary Supplement Health and Education Act, which determined that supplements should be regulated as foods, not drugs.

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That means the rules are less rigorous, which has unsurprisingly been a boon to the industry. Before 1994, there were about 4,000 dietary supplements on the market. Today they number approximately 85,000. Some 180 million Americans spend more than $32 billion a year on nutritional supplements, many of which are in the weight loss category.

"The law basically said manufacturers can do whatever they want in terms of safety and advertising," said Dr. Pieter Cohen, assistant professor at Harvard Medical School, who has studied the dangers of nutritional supplements extensively. "That allowed the industry to grow to where it is now."

There are so many products on store shelves and on the Internet, when you buy one, you really don't know what you're getting.

Sainah Theodore learned this the hard way when she decided to shape up and lose some weight. She wanted something to kick-start her regimen of running, swimming and Spinning. So the 27-year-old went to a Brooklyn, New York, health food store, where, a year and a half earlier, she'd bought some diet pills. Theodore had lost 15 pounds on the pills but eventually regained the weight. Now, she thought she'd try again.

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This time, she was directed to a supplement called Natural Lipo X. Theodore knew she was sensitive to caffeine (it makes her heart feel fluttery). According to a lawsuit she has filed against the store, Theodore was told that the pills did not contain caffeine and had "absolutely no side effects."

She said, "The language was very clear. And I trusted them."

That turned out to be a mistake. Two nights after starting Natural Lipo X, Theodore says, she began experiencing sleeplessness that would turn into complete insomnia; three days later, she stopped taking the pills. After about a week of little or no sleep, she had a breakdown. She lashed out at coworkers and friends and inexplicably stopped her car in the middle of an intersection one night.

"Something was definitely wrong," she said.

Theodore ended up being admitted to a hospital, where she was sedated. When she awoke, clearheaded, in the psych ward, she told a doctor about the Natural Lipo X. Later, she learned that the guarana-seed extract in the pills can contain twice as much caffeine as coffee beans. The lawsuit alleges that the pills also illegally included sibutramine, a stimulant that the FDA has warned can lead to anxiety, insomnia and even heart attacks; and phenolphthalein, a laxative ingredient now considered to be possibly carcinogenic. The label did not include the name and address of the manufacturer, which are required by the FDA. 

Even now, neither Theodore nor her lawyers know who made the pills. And the health food store has denied the allegations in the suit.

Theodore says she was unable to work for two months after she left the hospital. She adds that she worries about how this episode might affect her, professionally and personally, in the future.

"I'm embarrassed about the things I did," she said. "It's so not like me."

Stories like Theodore's have led some health experts to call for radical changes in the way diet aids are manufactured, marketed and regulated.

"Supplement producers should have to prove that their pills are safe and effective," Dr. Cohen said.

Last summer, Senator Dick Durbin (D–Ill.) proposed a law requiring supplement companies to submit a list of ingredients to the FDA, and for products to carry a label warning of possible adverse reactions. The industry opposes the legislation, and at press time, the bill was still in committee. For now, the only way to ensure your safety is to avoid diet supplements completely.

Karina Lujan wishes she'd never tried them. She says she first took OxyElite Pro in 2012 and then again in 2013. The 37-year-old Texan was already plenty active: She regularly hit the gym with her husband, ran up and down stadium stairs and went for bike rides with her three boys. But she says she wanted to lose the baby weight she was still carrying after giving birth to her fourth child. She thought OxyElite Pro might help rev up her workouts, so why not give it a try? 

One day after a dose, Lujan says she was walking up a flight of stairs when she suddenly felt out of breath. She started sweating and felt tremendous pain and pressure in her upper body, and her arm went numb. It turned out she was having a heart attack. 

"I couldn't understand it," she said. "You hear stories of things like this happening to people who are a lot older and out of shape, not someone who's young and healthy and has no history of heart problems. I was panicking."

Lujan survived, but 18 months later, she says she's still feeling the effects. She's taking blood thinners and medication to control her heartbeat. According to a lawsuit she filed against USPlabs, the manufacturer of OxyElite Pro, she has lost 10 to 20 percent of her heart function. She says she also has tachycardia, a condition that makes her heart beat too fast. She has yet to venture back to the gym or return to her bike riding. 

"How can I be like this for the rest of my life?" she asks.

The OxyElite Pro that Lujan bought contained DMAA, a stimulant sometimes called geranium extract. According to the FDA, it's an amphetamine derivative that can lead to heart attacks. In 2012, the agency issued letters to 11 manufacturers, including USPlabs, warning them that DMAA was illegal and calling on them to remove it from their products. Initially USPlabs questioned the FDA's legal basis for the order, but eventually the company eliminated the ingredient, recalled products from retailers and destroyed its own inventory when threatened with stronger FDA action.

In 2013, USPlabs released a new version of OxyElite Pro that contained aegeline, a synthetic version of a natural extract found in an Asian tree. In Hawaii last year, 44 people suffered either acute hepatitis or liver failure after taking it; one person died. Other cases of OxyElite-related injuries came to light. In all, nearly 100 people around the country experienced liver disease from the pills, and three of them needed liver transplants. In November last year, the FDA called on USPlabs to recall the product. USPlabs said it knew of "no valid concern about the safety of aegeline or OxyElite Pro" but, as "a precautionary measure," agreed to stop using the substance, issued a recall and destroyed remaining stocks.

USPlabs has denied responsibility for Lujan's heart damage, and her case is headed to court. Six Hawaiian consumers have also sued USPlabs.

Despite all of these problems, natural-sounding weight loss supplements continue to attract women. Karen Jacobs-Poles, a nurse at Penn Presbyterian Medical Center in Philadelphia, tries to be cautious about what she puts in her body. But the forty-something mother of three wanted to lose about 30 pounds, and exercising and eating fresh fruit and veggies didn't seem to be doing it. Then, one night in 2011, she saw a commercial for Slimquick, a diet supplement that billed itself as tailored to the problems women have losing weight, Jacobs-Poles said. "That really drew me in."

Slimquick claimed to be "the only weight loss supplement to help women lose up to 25 pounds." The berry-flavored drink mix contained green tea extract, and since she wanted to avoid potentially harmful chemicals, that appealed to her.

"I'd heard a lot about green tea and berries, and how they help your metabolism," she said. "I thought it sounded great."

Jacobs-Poles lost 15 pounds in about a month, with, she thought, no side effects. After a couple of weeks, though, she started to notice that she was more tired than usual.

"I figured it was just life and being constantly on the go," she said.

But it kept getting worse, and eventually she felt fatigued all the time. Then a coworker noticed that her eyes had turned bright yellow, a symptom of a sick liver.

"I was scared," Jacobs-Poles said. "I should have been feeling great, but instead I felt exhausted and awful."

According to a lawsuit Jacobs-Poles has filed against Slimquick, a blood test found dangerously high levels of liver enzymes. Doctors diagnosed her with jaundice, acute hepatitis and an enlarged liver. Her suit contends that this was a direct result of ingesting Slimquick ingredients.

"I thought I did everything right, all my due diligence," Jacobs-Poles said. "I was trying to be healthy. How was I to know it would make me so sick instead?"

She recalls it took almost a year before her liver functions were back to normal and almost another year before the exhaustion finally lifted. In their response to the lawsuit, the company that distributes Slimquick, Platinum US Distribution, denies responsibility for Jacobs-Poles's liver problems, saying that the products are made by third-party contractors.

An analysis by the National Institutes of Health's Drug-Induced Liver Injury Network of patients with liver illness from dietary supplement use found that cases increased from 7 percent to 20 percent from 2004 to 2012.

And while the potential for dangerous side effects is one huge reason not to take "natural" weight loss supplements, here's another: Most of these products don't work, said Melinda Manore, professor of nutrition at Oregon State University in Corvallis. In her review of hundreds of studies, Manore found that none of the products helped women lose more than a few pounds. 

"There is not one of these products I would recommend to anyone trying to lose weight," she said.

The only way to be sure you're safe and not sorry? Do what Jacobs-Poles and other women wish they had done: Leave those weight loss supplements on the shelf.

This article originally appeared on Self.com.

Additional reporting by Sara Angle.