Raspberry ketones have gained popularity in the weight loss industry, with claims of being a "miracle fat-burner in a bottle." However, it is important to separate fact from fiction when it comes to these supplements.
Unforuntaely this is definitely one of the cases in which the claims are pretty much fiction, despite what Dr. Oz may say. Ultimately ketones, (found in raspberries and other fruit) aren't actually anything to do with ketosis. Despite the similarity in name. Which sadly is ultimately what a lot of people are led to believe by some less than scrupulous companies.
Aside From The Name Where Did The Idea Raspberry Ketones Burn Fat Come From?
When it comes to the general public, we can see how people have been misled about raspberry ketones, but what got the scientists so interested in them to begin with. As we've all heard there's been research on the compound. Well, that's because the molecular structure of raspberry ketones is similar to capsaicin. Capsaicin being the compound found in chili peppers, which has actually been shown to increase calorie burn.  The other chemical they are similar to being synephrine, a stimulant. And studies suggest that stimulants can boost metabolism and promote fat breakdown. 
As a result, this led researchers to speculate that raspberry ketones might have similar effects.
Initially, in test-tube studies using fat cells from mice, raspberry ketones were found to increase fat breakdown by making the cells more responsive to the fat-burning hormone norepinephrine.  Additionally, they were found to increase the release of adiponectin, a hormone that plays a role in regulating metabolism and blood sugar levels. So far so good. The problem was when human trials began.
There have been several studies which showed that raspberry ketones did not result in weight loss in humans when compared against a placebo. 
The only positive weight loss study for raspberry ketones
The only study that comes close to examining the effects of raspberry ketones in humans used a combination of substances, including raspberry ketones, caffeine, garlic, capsaicin, ginger, and synephrine.
In this eight-week study, participants who took the supplement alongside calorie restriction and exercise experienced a greater reduction in fat mass compared to those who took a placebo. However, it is highly unlikely that the observed weight loss can be attributed solely to raspberry ketones, considering that both caffeinie, capsaicinginger and synephrine have all been shown to have an impact on weight loss themselves. 
Raspberry Ketones Side Effects
Some users report jitteriness, rapid heartbeat, and increased blood pressure when taking raspberry ketone supplements.
In terms of dosage, there is no scientifically-backed recommendation due to the lack of human studies. Manufacturers typically recommend daily dosages of 100-400 mg, divided into two doses. Whether or not that actually does anything or not is up for debate. Dr. Oz recommended taking 100 to 200 mg supplements of raspberry ketones with breakfast and lunch daily, which he claimed to be the chemical equivalent of about 90 pounds of fresh raspberries. This is largely where the 100-400mg a day idea came from, rather than much in the way of scientific backing.
There are a few extra at risks with Raspberry Ketones for certain groups.
- Diabetics: Raspberry ketones may affect blood sugar levels, so individuals with diabetes should consult with their doctor before using these supplements.
- Heart Issues and High Blood Pressure: Raspberry ketones can have an impact on blood pressure and heart rate due to their effect on norepinephrine. Individuals with heart issues or high blood pressure should avoid raspberry ketone supplements.
- COPD and Asthma: Raspberry ketones may worsen conditions such as COPD and asthma due to their effects on the respiratory system. It is advisable for individuals with these conditions to avoid using raspberry ketone supplements.
Are Raspberry Ketones A Scam?
Yes, there is almost no evidence to suggest that raspberry ketones do anything at all to help with weight loss in humans. The only study which showed them to be effective was when they were combined with caffeine and capsaicin, which as we mentioned have been provent independantly to work for weight loss. Studies on raspberry ketones as a stand alone showed they were not effective. In short, we don't recommend buying raspberry ketones as weight loss aid.
1 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6273101/
2 - https://pubmed.ncbi.nlm.nih.gov/23376413/
3 - https://pubmed.ncbi.nlm.nih.gov/31603036/
4 - https://pubmed.ncbi.nlm.nih.gov/28378858/
5 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3639826/