Countless supplements on the market claim to offer a quick way to drop excess weight.

Appetite suppressants are types of supplements that work by reducing appetite, thereby decreasing food consumption and promoting weight loss.

While certain types of appetite suppressants can only be prescribed by a doctor, many are available over the counter.

Here’s a review of 12 over-the-counter appetite suppressants, their effectiveness and safety.

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Conjugated Linoleic Acid (CLA) is a type of polyunsaturated fatty acid naturally found in foods like dairy and beef. It’s also sold in concentrated form as a weight loss supplement.

How it works: CLA has been shown to affect appetite-regulating genes and hormones. It may also boost the number of calories burned at rest, increase lean body mass and stimulate fat loss (1).

Effectiveness: While CLA reduces appetite and intake in animal studies, it has not been shown to reduce appetite in humans (2).

A 12-week study in 62 people demonstrated that 3.9 grams of CLA per day had no effect on appetite, body composition or the number of calories burned (3).

Though CLA supplements have been shown to promote fat loss in some studies, its impact on weight loss is small.

For example, a review of 15 studies found that overweight individuals who supplemented with CLA for at least six months only lost an average of 1.5 pounds (0.7 kg) more than people in the control group (4).

Side effects: Taking CLA may result in unpleasant side effects, such as diarrhea and gas. Supplementing long term may even cause serious complications, such as liver damage and increased inflammation (5, 6)

Summary CLA is a dietary supplement branded as an appetite reducer. However, human studies have shown that CLA has little impact on appetite and weight loss.

Bitter orange is a type of orange that contains synephrine, a compound that may be effective in reducing appetite.

Synephrine is structurally similar to the once-popular weight loss drug ephedrine, which has been banned from use in dietary supplements since 2004 due to serious side effects (7).

Bitter orange supplements are marketed to promote weight loss by reducing appetite and are available over the counter.

How it works: Bitter orange is believed to encourage weight loss by increasing your basal metabolic rate — or calories burned at rest — therein stimulating fat breakdown and suppressing appetite (8).

Effectiveness: Though research has shown that synephrine increases the numbers of calories burned, its effect on weight loss is inconclusive (9).

Because bitter orange is often combined with other compounds — such as caffeine — in weight loss supplements, it’s difficult to interpret its effectiveness.

A review of 23 studies found that 20–35 mg of synephrine per day increased metabolic rate and had a modest impact on weight loss.

However, some of the studies resulted in no weight loss or even weight gain after treatment with synephrine (10).

Side effects: Reported side effects of synephrine include increased heart rate, elevated blood pressure and anxiety.

However, it’s not yet understood whether synephrine alone or combined with other stimulants causes these symptoms (11).

Summary Bitter orange contains a compound called synephrine that may boost metabolism and encourage weight loss. However, research shows mixed results.

Garcinia cambogia diet pills are one of the most popular weight loss supplements on the market.

Made with an extract derived from the peel of the Garcinia gummi-gutta fruit, garcinia cambogia pills are used to suppress appetite and promote weight loss.

How it works: Garcinia cambogia extract contains hydroxycitric acid (HCA), which may reduce appetite by increasing serotonin levels in your brain and reducing the metabolism of carbohydrates (12).

Effectiveness: A review of 12 studies found that participants who supplemented with garcinia cambogia containing 1,000–2,800 mg of HCA per day for 2–12 weeks lost an average of 1.94 pounds (0.88 kg) more than those who consumed placebo pills (13).

Another study in 28 people demonstrated that garcinia cambogia was more effective at reducing appetite, increasing fullness and decreasing hunger than a placebo (14).

However, other studies have shown that garcinia cambogia has little to no effect on appetite or weight loss (15).

Side effects: Though generally considered safe, consuming garcinia cambogia may lead to side effects in some people, such as headaches, diarrhea, nausea, irritability and even liver failure in extreme cases (16).

Summary Some research shows that garcinia cambogia suppresses appetite and promotes weight loss.

Glucomannan is a type of soluble fiber derived from the edible roots of the konjac plant.

Because it can absorb up to 50 times its weight in water, it’s used as a weight loss supplement to increase fullness and reduce appetite (17).

How it works: Glucomannan is understood to encourage weight loss by reducing appetite, increasing feelings of fullness, slowing digestion and blocking the absorption of fat and protein (18).

Effectiveness: Studies on glucomannan’s impact on weight loss have provided inconsistent findings.

A review of six studies found that 1.24–3.99 grams of glucomannan per day for up to 12 weeks resulted in short-term weight loss of up to 6.6 pounds (3 kg).

However, researchers concluded that the results were not statistically significant and that larger and longer-term studies are needed (19).

Side effects: Glucomannan may cause side effects such as constipation, diarrhea, nausea and abdominal discomfort (20).

Summary Glucomannan is a type of soluble fiber that may promote short-term weight loss. However, results from studies are inconclusive.

Hoodia gordonii is a type of succulent plant traditionally used by indigenous people in southern Africa as an appetite suppressant.

Extracts from Hoodia gordonii are used in dietary supplements that claim to reduce appetite and boost weight loss.

How it works: Though the mechanism by which Hoodia gordonii suppresses hunger is unknown, some scientists link it to a compound called P57, or glycoside, which may impact your central nervous system and decrease appetite (21).

Effectiveness: There is little evidence to support the use of Hoodia gordonii to promote weight loss, and few human studies have examined the plant.

A 15-day study in 49 overweight women found that 2.2 grams of Hoodia gordonii per day taken one hour before meals had no effect on body weight or calorie intake compared to a placebo (22).

Side effects: Hoodia gordonii may lead to headaches, nausea, increased heart rate, high blood pressure and impaired liver function (23).

Summary Currently, no evidence supports the use of Hoodia gordonii for weight loss or reduced appetite.

Green coffee bean extract is a substance derived from the raw seeds of the coffee plant and is popularly used as a weight loss supplement.

How it works: Green coffee beans contain high levels of chlorogenic acid, which may inhibit fat accumulation. The extract also contains caffeine, which decreases appetite (24).

Effectiveness: A recent study in people with metabolic syndrome showed that those taking 400 mg of green coffee bean extract per day experienced a significant decrease in waist circumference and appetite compared to a placebo group (25).

An analysis of three studies found that overweight participants who took either 180 or 200 mg per day of green coffee extract for up to 12 weeks experienced an average weight loss of 6 pounds (2.47 kg) more than those taking placebos (26).

Side effects: Though green coffee bean extract is generally well tolerated, it may cause headaches and increased heart rate in some people.

Summary Several research studies have demonstrated that green coffee bean extract may reduce appetite and promote weight loss.

The guarana plant has been used for hundreds of years for various purposes, including appetite suppression (27).

How it works: Guarana contains more caffeine than any other plant in the world. Caffeine stimulates your nervous system and has been shown to decrease appetite and boost metabolism (28).

Effectiveness: Insufficient evidence exists to support the use of guarana to suppress appetite and promote weight loss.

However, test-tube and animal studies show that guarana extract may boost metabolism and limit fat cell production by suppressing certain genes (29).

Side effects: Because guarana is high in caffeine, it may cause insomnia, headaches, nervousness and increased heart rate and anxiety, especially when taken in high doses (30).

Summary Guarana — which is especially high in caffeine — may boost metabolism, but more research is needed to determine whether it suppresses appetite or promotes weight loss.

Acacia fiber, also known as gum arabic, is a type of indigestible fiber promoted as a means of suppressing appetite and promoting fullness.

How it works: Acacia fiber slows digestion, suppresses appetite, increases fullness and inhibits glucose absorption in your gut, which can all help manage weight (31).

Effectiveness: One six-week study in 120 women found that those taking 30 grams of acacia fiber per day lost significantly more body fat than those on a placebo (32).

Similarly, a study in 92 people with diabetes showed that 30 grams of acacia fiber daily for three months significantly reduced belly fat (33).

Side effects: Potential side effects of consuming acacia fiber include gas, bloating and diarrhea.

Summary Acacia fiber may encourage weight loss by increasing feelings of fullness and suppressing appetite.

Saffron extract is a substance derived from the stigma — or the female part of flowers where pollen is collected — of the saffron flower.

How it works: Saffron extract is believed to contain several substances that may increase feelings of fullness by boosting mood.

Effectiveness: One study in 60 overweight women demonstrated that those taking 176 mg of saffron extract per day experienced a significant reduction in snacking and lost more weight than women on a placebo pill (34).

Though these results are promising, larger and longer-term studies must be carried out to understand saffron’s role in appetite reduction and weight loss.

Side effects: Saffron extract is generally well tolerated but may cause dizziness, fatigue, dry mouth, anxiety, nausea and headache in some people (35).

Summary Some evidence supports the use of saffron extract as a way to reduce hunger and lose weight.

Guar gum is a type of fiber derived from the Indian cluster bean, or Cyamopsis tetragonoloba.

How it works: Guar gum acts as a bulking agent in your gut. It suppresses appetite by slowing digestion and increasing feelings of fullness (36).

Effectiveness: One study found that consuming 2 grams of guar gum per day resulted in significant reductions in hunger and decreased between-meal snacking by 20% (37).

Other studies demonstrate similar results, indicating that guar gum may be effective in reducing cravings and overall calorie intake (38).

However, guar gum has not been proven as an effective tool for weight loss (39).

Side effects: Guar gum may cause adverse side effects, such as abdominal discomfort, diarrhea, cramping, gas and bloating (40).

Summary Guar gum is a type of fiber that may be effective in reducing snacking between meals and decreasing overall calorie intake.

Forskolin is a compound extracted from the Coleus forskohlii plant.

How it works: Forskolin is purported to aid weight loss by reducing appetite, enhancing metabolism and increasing the breakdown of fat in your body (41).

Effectiveness: Human studies researching the effect of forskolin on weight loss and appetite suppression in humans are limited.

However, several studies demonstrate that doses of up to 500 mg of forskolin per day failed to reduce appetite, decrease food intake or encourage weight loss in overweight individuals (42, 43).

Side effects: Little is known about the potential side effects of Coleus forskohlii, though one study reported diarrhea and increased bowel movements (44).

Summary Forskolin seems to have little impact on appetite or weight loss. However, research on this supplement is ongoing.

Chromium is a commonly used mineral for blood sugar control, hunger reduction and decreased cravings.

How it works: Chromium picolinate is a highly absorbable form of chromium that helps reduce appetite and cravings by impacting neurotransmitters involved in regulating mood and eating behavior (45).

Effectiveness: A review of 11 studies in 866 overweight or obese people found that supplementing daily with 137–1,000 mcg of chromium for 8–26 weeks led to reductions in body weight by 1.1 pounds (0.5 kg) and body fat by 0.46% (46).

Side effects: Potential side effects related to chromium picolinate include loose stools, vertigo, dizziness, headaches and hives (47).

Summary Some research has shown that chromium picolinate may be effective in reducing appetite and encouraging weight loss.

Many supplements on the market claim to suppress appetite and boost weight loss.

However, very few of the dietary supplements listed above have sufficient evidence to suggest effectiveness in reducing appetite.

While certain supplements — such as acacia fiber, guar gum and chromium picolinate — have been reliably shown to decrease appetite, they may cause adverse side effects, such as headaches, diarrhea and abdominal discomfort.

There are many more effective, evidence-based ways to control appetite, reduce snacking and lose weight without relying on dietary supplements.

Cutting out processed foods, reducing your overall calorie intake and increasing your activity levels are tried-and-true methods that will put you on the path to weight loss.