Green coffee bean extract is a new ingredient on the market. It has strong anti-oxidant properties similar to other natural anti-oxidants like green tea and grape seed extract. These beans have polyphenols which act to help reduce free oxygen radicals in the body (in other words acting as good antioxidants). Green coffee bean extract is sometimes standardized to 30 to 50% chlorogenic acid, a compound present in coffee which has long been known for its beneficial properties.
   Boiled coffee drinks contain cafestol which is associated with the negative effects of using coffee as a stimulant, this is not present in green coffee beans or the extract.
   This natural supplement has been mentioned on the  Dr. Oz TV program several times as a potential fat burner that helps with weight loss. Is this claim true or are the claims overly enthusiastic? The hype began in September 2012 when Dr. Oz nationally introduced green bean coffee extract as a "fat burner that helps women lose weight." It now appears that the promises exceeded the actual benefits.
   A search on Medline in 2015 did not reveal any new human experiments with this product since 2012.

Availability by herb and vitamin suppliers
Green coffee bean is sold in a variety of extracts usually from 30 percent to 50 percent chlorogenic acid concentration. For appetite control I suggest Diet Rx which is more effective.

Buy Green Coffee Extract pills, high quality, or Diet Rx which is a more potent appetite suppressor

Research and benefit
Although this supplement has been promoted as a weight loss pill, there is only limited human research regarding this potential benefit. If you truly wish to shed some pounds, a comprehensive dietary and lifestyle approach is necessary as mentioned in this article on natural weight loss

Review of studies regarding its influence on body weight - retracted study
Diabetes Metabolic Syndrome Obesity 2012.
Randomized, double-blind, placebo-controlled, linear dose, crossover study to evaluate the efficacy and safety of a green coffee bean extract in overweight subjects.
Department, University of Scranton, Scranton, PA, USA.
A 22-week crossover study was conducted to examine the efficacy and safety of a commercial green coffee extract product GCA™ at reducing weight and body mass in 16 overweight adults. Subjects received high-dose GCA (1050 mg), low-dose GCA (700 mg), or placebo in separate six-week treatment periods followed by two-week washout periods to reduce any influence of preceding treatment. Significant reductions were observed in body weight, body mass index, and percent body fat, but with no significant changes to diet over the course of the study. The results suggest that GCA may be an effective nutraceutical in reducing weight in preobese adults, and may be an inexpensive means of preventing obesity in overweight adults.

Diabetes Metab Syndr Obes. 2014. Randomized, double-blind, placebo-controlled, linear dose, crossover study to evaluate the efficacy and safety of a green coffee bean extract in overweight subjects [Retraction] This retracts the article "Randomized, double-blind, placebo-controlled, linear dose, crossover study to evaluate the efficacy and safety of a green coffee bean extract in overweight subjects" in volume 5 on page 21, which was published in final edited form. Vinson JA, Burnham BR, Nagendran MV. Diabetes, Metabolic Syndrome and Obesity: Targets and Therapy. 2012. The sponsors of the study cannot assure the validity of the data so we, Joe Vinson and Bryan Burnham, are retracting the paper.

BMC Complement Altern Med. 2006. Inhibitory effect of green coffee bean extract on fat accumulation and body weight gain in mice.

High blood pressure benefit
Perhaps it may have some benefit in lowering blood pressure, but certainly more studies are needed to confirm initial findings.

Clin Exp Hypertens. 2006. The blood pressure-lowering effect and safety of chlorogenic acid from green coffee bean extract in essential hypertension.
Health Care Products Laboratories, Kao Corporation, Tokyo, Japan.
Chlorogenic acids (CGA) in green coffee bean extract (GCE) reduce blood pressure in spontaneously hypertensive rats and humans. The authors examined the blood pressure-lowering effect and safety of CGA in patients with mild hypertension through a placebo-controlled, randomized clinical trial. Subjects were randomized to receive treatment with CGA (140 mg/day) from GCE or placebo. Blood pressure, pulse rate, body mass index, routine blood test, hematochemistry, urinalysis, and subjective symptoms were recorded throughout the study. In the CGA group, but not the placebo group, blood pressure (systolic and diastolic) decreased significantly during the ingestion period. There was no difference in body mass index and pulse rate between groups, nor were there any apparent side effects. Thus, CGA from GCE is effective in decreasing blood pressure and safe for patients with mild hypertension.

Hypertens Res. 2005. Antihypertensive effect of green coffee bean extract on mildly hypertensive subjects.

Improved blood vessel action, circulation
Green coffee bean extract improves human vasoreactivity.
Hypertension Research. 2004.
Green coffee bean extract contains chlorogenic acid as a major phenolic compound, and it in turn contains ferulic acid as a metabolic component that acts on nitric oxide (NO) derived from the vascular endothelium. In this study, the effects of green coffee bean extract on blood vessels were evaluated in healthy males. The subjects were 20 healthy males with reduced vasodilation responses measured by strain gauge plethysmograms (SPG) to ischemic reactive hyperemia. Of the 20 subjects, 10 ingested a test drink containing green coffee bean extract (chlorogenic acid 140 mg/day), and the other 10 ingested a placebo drink for 4 months. During the ingestion period, SPG, pulse wave velocity (PWV), and serum biochemical parameters were measured, and acceleration plethysmograms (APG) were taken. The reactive hyperemia ratio (RHR) in the test drink group began to increase after ingestion for 1 month and was significantly higher than that in the placebo group after ingestion for 3 months and 4 months. In addition, after ingestion for 4 months, the test drink group showed a significant decrease in the plasma total homocysteine level compared with the pre-ingestion level. However, there were no significant differences in PWV or APG between the test drink group and the placebo drink group. The improvement in RHR after ingestion of a drink containing GCE suggested an improvement in vasoreactivity by this component.

Diabetes and blood sugar
Dietary supplementation with decaffeinated green coffee improves diet-induced insulin resistance and brain energy metabolism in mice. Nutr Neuroscience. 2012.

What do the beans contain?
Polyphenols including chlorogenic acids (caffeoylquinic acids and dicaffeoylquinic acids). Chlorogenic acids are cinnamic acid derivatives with biological effects mostly related to their antioxidant and antiinflammatory activities. Caffeoylquinic acids and dicaffeoylquinic acids are the main chlorogenic acids found in nature. Contains caffeine (I think the amount of caffeine is small but I am not sure yet) which has positive and negative attributes depending on dosage used, timing, and frequency.

Green coffee bean extract is made from the green beans of the coffea Arabica plant. There are two types of coffee plants, arabica and robusta... the arabica is higher in quality and higher in chlorogenic and caffeic acids, two primary compounds responsible for anti-oxidant activity.

My experience and side effects
I have only take this natural product two days in a row, 2 pills in the morning. I did notice appetite suppression but it was mild compared to Diet Rx. I also noticed feeling more alert and my vision was clearer. Side effects may include shallow sleep if taken later in the day. I tried it several months later and again I noticed slight visual clarity within an hour of taking two pills.

Interview questions asked by a magazine writer:
Can people really lose weight with these green coffee beans or is it just over-hyped about and does less than people think?
   The research on this topic is quite limited, just a handful of studies have been done on the use of green coffee bean extract supplements and weight loss in humans. Even though there have been positive results, I prefer having a chance to review a few more before having more confidence.

What's the magic ingredient in green coffee beans that makes weight loss possible?
   It's probably a combination of several ingredients including chlorogenic acids and caffeine.

If green coffee beans are so healthy for people, why don't they sell them in stores?
   I don't know much about their availability in coffee shops but they are sold over the counter as dietary supplement pills.

As a doctor, have any of your patients used green coffee beans? If yes, can you tell me their experience with it?
   Thus far no major side effects have been mentioned in the medical literature, but, as with any new dietary supplement, when hundreds of thousands of new people start using it with many of these individuals taking various medications or having existing medical conditions such as heart disease or hormone imbalances, it is possible adverse reactions could occur in some individuals that at present are difficult to predict.

Questions
Can a green coffee extract be taken the same day as tongkat ali, choline, dmae, or carnosine and other dietary supplements and herbal medicines? I forgot to ask about saw palmetto.
    Many of these nutrients and herbs you mention above are very stimulating, so it would be preferable not to take them the same day or to take lower dosages.

Is coffee a functional food?
The worldwide use of coffee for social engagement, leisure, enhancement of work performance and well-being is widely recognized. Depending on the quantities consumed, it can affect the intake of some minerals (K, Mg, Mn, Cr), niacin and antioxidant substances. Epidemiological and experimental studies have shown positive effects of regular coffee-drinking on various aspects of health, such as psychoactive responses (alertness, mood change), neurological (Alzheimer's and Parkinson's diseases) and metabolic disorders (diabetes, gallstones, liver cirrhosis),  increase the effectiveness of pain killers, especially for migraine medications, and gonad and liver function. Despite this, most reviews do not mention coffee as fulfilling the criteria for a functional food. Unlike other functional foods that act on a defined population with a special effect, the wide use of coffee-drinking impacts a broad demographic (from children to the elderly), with a wide spectrum of health benefits. However, there is a down side to coffee drinking. It can cause anxiety and blood pressure problems, and it could also cause or aggravate heart rhythm abnormalities. Hence, it is possible to claim that coffee, when limited to one cup a day could be considered a functional food, but not when 3 or more cups are drank a day, particularly if the coffee is ingested later in the day and causes insomnia.