If every supplement marketed as a fat melting miracle actually worked, the obesity epidemic wouldn't exist, and we would all be thin (or ripped) and happy. But do some of them work? Is it just a matter of finding the right pill?

Today we'll look at a handful of the most popular and buzz-worthy supplements that claim to help people lose weight. Do they work? Are they safe? Let's dig in.

Weight Loss Supplements' Best Kept Secret

Some don't work at all. A few do. But here's the mostly-hidden truth: Most of the ones that "work" show very small effects, and usually only when used in conjunction with diet and exercise.

That sounds like a no-brainer, like, of course I'm going to diet and exercise if I'm interested in weight loss. But the real life decision you're trying to make is this: If I'm already dieting and exercising, will the supplement help me drop more weight than I could on my own? And if I don't intend to diet and exercise (so not you, dear reader, but your lazy friend), what's the point of taking a pill that won't work by itself?

So we have to distinguish between what sorta kinda "works," and what's worth taking. And we also have to look at the safety profile. There's no such thing as a drug that has purely beneficial effects. If something can change and affect your body, there will be risks and benefits to balance against each other. Yes, even if the drug or supplement is "natural."

One last caveat: some supplements aren't supported by science at all. Somebody decides that an obscure herb would look good on a product label, so they start selling it with wild claims about weight loss without any basis for those claims. Remember the acai berry supplements that were widely advertised a few years ago? There were no studies on acai in humans. The berry was tested in rats—but didn't make them lose weight.

A few popular supplements and what they really do

Garcinia cambogia

What it's supposed to do: Shut down the body's ability to store fat, and/or decrease your appetite so you eat less.

What it actually does: It works in rats, so if you're an overweight rat, this is the supplement for you. In humans, the evidence is disappointing: two trials found no difference in weight loss between people taking Garcinia and people taking a placebo. A third study found a barely detectable difference: people taking Garcinia lost anywhere between half a pound and 6.6 pounds, while people on the placebo lost up to 5.3 pounds.

That difference is statistically significant, so if you believe that one study (and ignore the two others) you could say Garcinia "works." But consider the cost, literally: The average benefit was only about one pound of weight loss over the course of the study. The study ran for 12 weeks at a dose of 1200mg Garcinia per day (400mg before each meal). That's $90 of Garcinia at GNC prices, or $42 at Wal-Mart prices.

Would you pay that much for a one-in-three chance of losing one pound over the course of 12 weeks? We don't even know if it would work longer-term, or how likely you are to gain it back.

Bottom line: Probably doesn't work; not worth it even if it does.

Hoodia gordonii

What it's supposed to do: Suppress your appetite, like the hunter-gatherers who chewed on this plant during famines.

What it actually does: Probably nothing good, and maybe something bad.

Hoodia tastes bitter, and that's probably the only reason that chewing on it might decrease your appetite. The active ingredient gets destroyed in the stomach, and probably doesn't make it to the brain or anywhere else it might be helpful.

As a supplement, it hasn't resulted in weight loss for humans. It works in rats, but even if you're a rat, I wouldn't recommend this: it seems to be toxic to them at fairly small doses.

Bottom line: Probably useless.

Ephedra

What it's supposed to do: Raise your metabolism and body heat, causing your body to burn extra calories.

What it actually does: Exactly that, but it might also kill you.

Hey, I said “might!” Examine.com (a great resource for checking out the science behind supplements) writes that "while dietary supplements containing ephedrine alkaloids have been used with an acceptable margin of safety and efficacy by many individuals, they can be downright dangerous for those with certain underlying medical conditions."

Ephedra was linked to 155 deaths before it was banned in the US, including deaths of athletes from heat stroke and heart problems. (It's not possible to prove that ephedra directly caused these deaths, but they match up with the way ephedrine, its main active ingredient, is known to work.)

At least ephedra works, right? Studies consistently show that it helps with weight loss, at least in the short term (up to six months). What happens after that, we don't know. Ephedra is a stimulant, and seems to work better when paired with caffeine. Studies suggest you'll lose about an extra 2 pounds per month if you take ephedra along with diet and exercise, versus diet and exercise alone.

Bottom line: It works, but is illegal in the US and carries significant risks. If you really feel like this is worthwhile, definitely take it under medical supervision.

Legal "ephedra"

What it's supposed to do: Same thing as ephedra

What it actually does: Nobody really knows.

The word "Ephedra" comes from the scientific name of the ma huang plant, Ephedra sinica. But there are around 70 other species in the Ephedra genus, including mormon tea (Ephedra nevadensis). These share a name and thus a reputation with the Ephedra we know and love, but they're not very well studied, and may have little to no ephedrine (the active ingredient). Really, without studies, it's impossible to say whether they work.

A different type of supplement, marketed the same way, is bitter orange. It has a component called synephrine that looks chemically similar to ephedrine, but there's no evidence supporting it as a fat burner in humans.

Bottom line: If it actually works, it probably has similar safety issues as ephedra. But then again, it might not be equivalent at all.

What You Need to Know

Most weight loss supplements share the same story as Garcinia and Hoodia: they're just expensive placebos. A few are more like Ephedra: effective, but not necessarily worth it. (Cigarettes, for example, seem to cause weight loss but are definitely not recommended.)

One problem with all supplements in the US is that we can never totally trust the contents. If you believe that supplements have to be approved to be legally sold, or that dangerous supplements would carry a warning label, you would be wrong—but also in good company, since more than half of Americans share these misconceptions.

There's also no independent quality control. It happens sometimes that supplements don't contain the snazzy ingredients that you paid so much for. And there have been plenty of cases where a supplement contained ingredients that weren't on the label—in some cases, dangerous drugs, and in others, drugs that caused athletes to later test positive for performance enhancers, even though the athletes themselves thought they were clean. This is illegal, but it happens: the FDA doesn't have the funds to go after every sketchy-looking pill bottle.

I can’t tell you whether or not to take a supplement, but It's important to realize that supplements (weight loss or otherwise) are a bit of a gamble even if science backs up the claims. And as we've seen, it often doesn't.