Turn on the TV or radio, browse the Internet or flip through a newspaper or magazine, and you’ll undoubtedly come across advertisements for over-the-counter weight-loss supplements. These so-called “fat blockers” and other products pose as magic pills that can give you a trim, healthy body with little trouble on your part.

The Food and Drug Administration  (FDA) doesn’t approve such products before they go on the market and is only empowered to act if a health risk is found once they are in common use. So when it comes to weight-loss supplements buyer beware! Ephedra, which used to be a common ingredient in weight loss supplements, illustrates that all too well. The herb, also known as ma huang, is related to the hormone adrenaline and revs up the body’s systems. In doing so, it increases heart rate and blood pressure and can stress the heart and blood vessels, which has led to heart attacks or sudden death in some people. Because of the turmoil, other ingredients have taken ephedra’s place on the shelves – but are they any safer?

Here are some commonly found ingredients in weight-loss supplements and what you should know about them. 

Bitter Orange: This ingredient contains synephrine. Because it is similar to ephedra both in chemical make-up and possible side effects, bitter orange should be taken with caution.

Chitosan: Processed from a protein found in the shells of insects and shellfish, chitosan packagers claim it keeps fat from being absorbed in the intestine. However, a randomized, placebo-controlled trial showed no significant difference between people who took a chitosan product and those who took placebo.

Chromium: A mineral claimed by some manufacturers to decrease blood sugar and help with weight loss, chromium has not been proven to have any positive effects. However, chromium supplements have been shown to damage chromosomes, which house the body’s DNA.

Cider vinegar: Thought to interfere with the digestion of carbohydrates, vinegar held down after-meal sugar spikes and was associated with moderate weight loss in two separate studies. But don’t run out for vinegar pills or capsules; it’s the active acetic acid in fresh vinegar that’s thought to have an effect on metabolism. Instead, have vinaigrette dressing or pickles with your lunch or dinner.

Guarana: This tropical berry is loaded with caffeine – about 30 percent more than coffee. Some studies show caffeine increases metabolism, but not necessarily at burning, and it tends to raise blood pressure.

Gymnema sylvestre: An extract from the leaves of this woody tropical plant from India is supposed to work as a “sugar destroyer.” But for weight loss, the evidence isn’t clear. In one study, people lost weight after eight weeks of taking a product containing Gymnema sylvestre, but the product also contained chromium and hydroxycitric acid. In addition, the subjects’ diets were limited to 2,000 calories per day and they participated in a walking program, so it’s not possible to say what caused their weight loss.

Hoodia gordonii cactus: The flesh of this cactus is thought to suppress appetite. Interest in hoodia skyrocketed following a “60 Minutes” report on the plant’s effects. Clinical trials are underway, but as yet, there is no conclusive evidence that extracts of the plant are a safe and effective diet aid for humans. Hoodia plants are hard to grow and, therefore, are scarce, so watch for products that falsely claim hoodia as an ingredient.