Most of our unhealthy habits stem from doing what’s easier or cheaper. But there’s nothing cheap or easy about taking vitamins and herbal supplements — and there’s no credible evidence they offer any benefits for the average person.

Anyone walking into a grocery store can quickly see that dietary supplements are big business. Vitamins and herbal supplements command a significant chunk of floor space.

The pills, capsules, and powders make up 5 percent of all grocery sales in the United States. Their profit margins, however, are about 10 times as high as those of food items.

Supplements, in fact, keep many small natural groceries in business, according to James Johnson, a senior market analyst for the trade publication Nutrition Business Journal.

Most Americans, hoping to improve their health, spend some of their hard-earned cash on these products.

About half of Americans take multivitamins. Many also take individual vitamin supplements. And roughly one in five U.S. adults uses herbal supplements.

All told, Americans will spend $21 billion on vitamins and herbal supplements in 2015. If protein powders are included, supplements are as big a market as all organic foods combined.

Related News: How ‘Superfoods’ Like Bulletproof Coffee Get Popular »

Many of the shortcomings in the American diet are linked to economics. We eat fast food because it’s cheap. We buy more processed foods and fewer fruits and vegetables because the packaged goods cost less and keep longer.

We gripe about the price tag on organic foods. Then we spend $21 billion a year — 9 cents for every adult in the nation — on products that are neither tasty nor cheap in hopes they will counter the damage we’ve done.

And American consumers do this almost entirely on their own.

The U.S. Preventive Services Task Force (USPSTF), an independent group of doctors, opted in 2013 not to recommend regular use of any multivitamins. It doesn’t recommend the use of any herbal supplements, and it advises consumers not to take beta-carotene or vitamin E.

In 2011, the Iowa Women’s Health Study found that, when other variables were excluded, those who took vitamins died sooner than those who didn’t. Only vitamin B and calcium had a small positive effect. The study followed more than 38,000 women for 20 years.

Herbal supplements are difficult to test, Dr. Carol Haggans, RD, of the Office of Dietary Supplements at the National Institutes of Health, told Healthline. There are multiple species of many common herbs on store shelves, and products often include more than one part of the plant.

Steve Mister, president of the supplements industry group the Council for Responsible Nutrition (CRN), agreed with Haggans’ assessment. Asked to cite herbs for which he’d seen compelling evidence, he named saw palmetto and echinacea but acknowledged that research studies have reached contradictory conclusions. Mark Blumenthal, founder and executive director of the American Botanical Council, mentioned St. John’s Wort to treat major depression, but research is mixed for it as well.

But there’s no lack of research on vitamins. Several large, long-term studies have failed to come up with evidence to suggest there’s any reason to take multivitamins or any of the common single-letter vitamins as a preventative measure.

The supplements industry finds fault with the science. Mister pointed instead to an outlier study that did find that multivitamins reduced the risk of cancer in an older and largely male study group of physicians.

A few vitamins are recommended under specific circumstances.

Vegans and those over 50 may want to consider adding vitamin B12, which is found naturally mainly in animal products and can be difficult for older Americans to digest.

Women who are or may become pregnant are advised to take folic acid to guard against neural tube birth defects.

The USPSTF recommends vitamin D for people over 65 who are at risk of falls. Some doctors recommend it for their younger patients as well because sunscreen and more time spent indoors limit our natural production of the vitamin.

Yet, consumers who don’t fall into any of these risk groups spend upward of $15 a month on vitamins. Market watchers and dieticians say consumers do this because they know they eat poorly but can’t find the time to eat more vegetables, fruits, and legumes. (There’s some evidence that a diet rich in fruits, vegetables, and legumes prevents cancer, heart disease, and obesity.)

“What people are saying is, ‘I know I should be eating better. I feel bad about that, but I either don’t want to do it or I don’t have the motivation. I’m going to get a multivitamin and that’s going to make me feel a little better — at least I’m doing that,’” said Joan Salge Blake, MS, RD, LDN, a dietician at Boston University.

An American eating a pretty average diet runs little risk of developing a vitamin deficiency, according to the Office of Dietary Supplements in the National Institutes of Health. Only about 10 percent of Americans have vitamin deficiencies, according to a national survey from 2003-2006.

The rest of us can easily get what we need, even with the minimum requirements of fruits and vegetables and the occasional bit of enriched flour or breakfast cereal.

“I encourage [patients] to look at their food choices and make changes in food first before resorting to pills,” said Katie Ferraro, MPH, RD, a dietician at the University of California, San Francisco (UCSF).

Learn More: The Symptoms of Vitamin B Deficiency »

Vitamins, and before them elixirs, have long held a particular sway over American consumers. The Food and Drug Administration (FDA) was established in 1906 to solve the same problem American consumers still, to a lesser degree, face: What is a genuine medicine and what is snake oil?

The Federal Trade Commission (FTC) came along about a decade later, tasked with making sure that marketers don’t make false or unsubstantiated claims about their products.

Since then, both agencies have had their hands full trying to figure out how best to regulate vitamins and supplements, and how to enforce those regulations for millions of products.

Supplement makers have to adhere to the FDA’s good manufacturing guidelines. They’re required to accurately identify the ingredients their products contain — but as the recent crackdown by the New York Attorney General’s office reveals, they don’t always do so.

With a limited budget, the FDA only spot tests about 1 percent of the 65,000 dietary supplements on the market, according to Todd Runestad, editor of the trade publication Functional Ingredients and the Engredea reports.

Dietary supplement makers aren’t required to prove their supplements have any effects on health. And only ingredients developed after 1994 must be tested for safety before they hit the shelves.

If a supplement results in “adverse events,” however, the FDA can pull it. The agency used this authority to ban the herbal weight loss supplement ephedra in 2004 after it led to eight deaths. In 2013, the FDA recalled OxyElite after it led to several cases of liver failure.

“There are a lot of consumers out there who think that these products wouldn’t be on the market with these claims if they hadn’t been reviewed by some government agency. There’s a large number of people who think that and it’s a myth,” said Rich Cleland, assistant director of the FTC’s Division of Advertising Practices.

The FTC, meanwhile, guards against false advertising. That job sometimes requires poring over the scientific studies on which marketers base their claims to see if they are real or junk science, according to Cleland.

Critics think the loose government regulations allow supplements to remain unchecked while being advertised as medical care. But others think regulators are in the pockets of special interests that don’t want supplements on the market in the first place.

“There’s lots of research, it’s just that the disease treatment system does not acknowledge that there are more than two states — healthy and diseased. The FDA is a wholly owned subsidiary of Big Pharma, and they’re there to protect the interests of Big Pharma,” said Runestad.

There have been a number of efforts to develop tighter regulatory control. In 1976, the FDA moved to regulate vitamins that contained more than 150 percent of the recommended daily allowance as drugs. Congress forbade the agency from doing so.

In the early 1990s, Congress considered several bills that would have expanded the powers of the FDA. The Nutritional Labeling and Education Act of 1990 imposed stricter labeling rules on food products. At the urging of Senator Orrin Hatch, a Utah Republican, the law exempted dietary supplements. Utah is home to many dietary supplement companies, whose combined value exceeds $5 billion, according to NASDAQ.

In 1994, the supplements industry scored a big legislative win. Regulations were loosened under the Dietary Supplement Health and Education Act (DSHEA), sponsored by Hatch and Tom Harkin, a now-retired Iowa Democrat whose largest corporate donor over the course of his career was the dietary supplements giant Herbalife.

DSHEA, which insiders pronounce duh-SHAY, didn’t go so far as to allow herbal supplements to claim on their labels that they cure, treat, or prevent any diseases, but it ushered in more general health claims, such as “supports healthy immune function.” Passage of the law led to an explosion in the industry.

Since then, lawmakers have tried to patch some of the problems with DSHEA, but the industry has resisted.

In 2006, a new law required dietary supplement makers to report serious adverse health events linked to their products. But a 2010 law requiring reporting of all adverse events died in the Senate.

And in 2013, a bill that would have given the Institute of Medicine the power to screen the ingredients in supplements also died without reaching a vote. Supplements makers lobbied hard against both bills.

Plan Ahead: Your Severe Allergy Toolkit»

For their part, consumers seem content. Even with the Preventive Services Task Force concluding that vitamins don’t prevent cancer or heart disease, the market grew 3 percent in 2013.

In recent years, the industry has been growing about as fast as the Chinese economy, according to numbers from Euromonitor. It has expanded 40 percent since 2008.

The trouble is, there’s really no way for consumers to know what they’re buying.

Although the FDA only tests a tiny fraction of vitamins and herbal supplements, it regularly turns up banned and prescription drugs in weight loss and sexual enhancement supplements.

These supplements inhabit the darkest corner of the industry, driven by high profit margins and a small chance of getting caught, experts say.

“DSHEA creates perverse incentives for unscrupulous manufacturers to out-compete legitimate companies by adding undeclared, illegal ingredients including prescription medications, banned drugs, and even entirely novel chemical compounds,” Dr. Pieter Cohen, an assistant professor at the Harvard Medical School, wrote last year in the Harvard Public Health Review.

Cohen and some colleagues tested supplements that were back on the shelves about a year after being recalled by the FDA for containing prescription drug ingredients. More than 60 percent still contained the banned drugs.

Sometimes new herbal ingredients, particularly in weight loss products, prove just as dangerous. A novel ingredient in the weight-loss supplement OxyElite was linked to several cases of liver failure. The unsold product the company was forced to destroy was worth $22 million.

Mister, of the CRN, called those who doctor their herbal products as “a part of the industry we try hard to marginalize.”

Health-oriented herbal supplements and vitamins are a safer bet, but they aren’t trouble-free.

Last month, the New York Attorney General’s office conducted its own testing of six popular herbal supplements — including garlic, echinacea, and saw palmetto — offered by major retailers.

According to the tests, 20 percent of the products matched their labels, while nearly 80 percent contained none of the product on the label or were contaminated with other plant material. None of the unlabeled ingredients was dangerous, except potentially to those with food allergies.

Industry groups contend that the government used the wrong testing method. A garlic supplement doesn’t contain garlic; it contains the active ingredient in garlic, they argue.

But Dr. Steven Heymsfield, a nutrition and obesity expert at Louisiana State University, said that critique is laughable. The industry works by sowing small seeds of doubt about scientific studies of their products, he said.

“A high-school student could do those analyses,” he said. “Give me a break.”

For Cohen, that is the best reason to stick to foods thought to have health benefits, such as turmeric, ginger, and cranberry, instead of buying their packaged equivalents.

“There may be evidence that some botanicals in their pure state have medicinal effects,” he said. “But consumers need to realize that what they’re purchasing in a bottle is completely different from what an ancient herbalist would have used, making it extremely unlikely that these highly processed products are going to confer any of the theoretical health benefits — even if they’re made from the plants they say they are.”

Heymsfield has done scientific research of his own on whether herbal weight loss supplements work. In addition to early research into ephedra, he worked in 1998 with a company that was interested in marketing garcinia cambogia, an ingredient in the tropical fruit tamarind also sometimes called hydroxycitric acid.

The study, published in the Journal of the American Medical Association, found that garcinia cambogia made no difference for weight loss. Others in the supplements industry critiqued the findings, but no study has refuted Heymsfield’s results. Because any unpatented substance found to promote weight loss would be wildly profitable, a lot of companies have looked into garcinia cambogia.

“Nestle, Dannon — all these companies have used a high-power microscope to look at those things and have walked away,” Heymsfield said.

But in late 2012, the telegenic Dr. Mehmet Oz called garcinia cambogia “a revolutionary fat buster.” Google search queries for the obscure herb shot up. After Oz went before Congress and admitted there was no scientific evidence to support this or other product endorsements he’d made on his show, search volume fell off, but not by much.

What is a fair way to regulate ingredients like garcinia cambogia?

“You don’t want to make foods require the same level of evidence that drugs do — nobody could afford the foods,” Heymsfield said. “There must be a lower level of claims that are acceptable. Maybe I’m conservative on this, but I think if you imply a claim or you make a claim you should have to prove it scientifically and usually that means doing a genuine study. Otherwise you’re in a no man’s land.”

Between continued consumer interest, grocery store profits, and manufacturers’ lobbying muscle, vitamins and herbal supplements probably aren’t going anywhere anytime soon.

So how can shoppers protect themselves and their pocketbooks?

The doctors and dieticians Healthline spoke to recommended waiting for a doctor to advocate any vitamins or supplements — or at the very least, clearing them with a doctor first.

Some herbs can interact badly with certain prescription medicines, and vitamins if taken in high dosages can be dangerous.

“If one multivitamin provides 100 percent daily value, it doesn’t mean that one providing 1,000 percent is 10 times better,” said USCF’s Ferraro.

For those who want to take a single multivitamin as an insurance policy, mainstream medical advice can be boiled down to indifference.

“You’re not likely to do any harm with a multivitamin, but it may not be doing any good either,” said Haggans of the NIH.

Stand-alone vitamin supplements, unless recommended by a doctor, are riskier.

“When people start buying individual supplements, the doses tend to be a little higher. You need to be a little more wary of it when you start doubling up on things. It can happen that people go too far,” said Haggans.

None of the dieticians or doctors Healthline spoke to endorsed any specific herbal supplements.

Even Runestad, an advocate who takes many vitamins and other supplements personally, acknowledged there is “a problem of ingredient adulteration.” But it’s easy to stay safe by buying reputable brands. He recommended several brands including Gaia Herbs, Herb Farm, Source Naturals, Doctors Best, and Nature’s Way.

Cleland of the FTC also specifically cautioned against buying unfamiliar brands online.

In the end, all conclude that healthy food is the cheaper and the better option.

“We’re smarter than we were years and years ago,” said dietician Blake. “Now we know there are phytochemicals and fiber in fruits and vegetables that are working to prevent cancer, and you can’t put those in a pill.”

Keep Reading: Vitamin Cheat Sheet »