Thermogenics are a widely used and often believed to be an excellent accessory or even a main system for weight loss. In this article, we will discuss the nature of thermogenics, the most popular ingredients in thermogenic supplements (caffeine, ephedrine, capsaicin, green tea, and a mixture), if thermogenics work, and how well they might work. By the end of this article you will have a scientifically sound understanding of thermogenics and their worth – let us take on this challenge together.

What is a thermogenic?

As you may know, energy is measured in heat production (look up direct calorimetry, as a prime example), and as such, the more heat our body produces, the more energy it uses. Energy, in nutritional terms, is measured in calories, so a thermogenic supplement increases the body’s heat production, which means it increases the body’s caloric use [1].

Here is an example of direct calorimetry. It used to be the way we figured out how much energy a person expends by gathering the heat they release in an insulated chamber.

What are popular thermogenics?

It is pointless for me to list the seemingly impossible number of thermogenic products that have been used in the past, are currently being used, and will be used; however, these products have different doses of a series of repeatedly seen constituents, and we will look into the most popular of these. We will look into ephedrine, caffeine, capsaicin, and a mixture of some of these constituents.

Do thermogenics work?

Well, since there is a lot of controversy over the efficacy of thermogenics, it will be necessary for us to investigate several scientific, peer-reviewed sources to establish an answer that we can proudly claim as accurate. To do this, we must not only prove that these products increase caloric expenditure, but also address for how long (is it significant or insignificant?), how much of an increase, and how much is the appropriate dose to see an increase, if any. So, without further ado, let us break this down between constituents.


Caffeine has been a popular stimulant for quite a long time and has been consumed in copious amounts for seemingly forever. In terms of its increase in caloric expenditure, there seems to be evidence that caffeine, alone, does lead to an increase in caloric expenditure [2]. Caffeine increases resting metabolic rate (RMR) by 3-4% for around 2.5 hours if 100mg are ingested [2]. So, the absolute amount of energy expenditure increase is relative to the person, but it can be statistically significant. That said, a person measures their caloric intake by the day, so we need to adjust this value to accommodate this measure.  

First, we need to be clear that resting metabolic rate is not total daily energy expenditure (TDEE), but only a part, albeit large part, of TDEE. So, assuming a person has a 1800 calorie RMR, they would need to ingest 100mg of caffeine every 2-3 hours to see a continuous 4% increase in caloric expenditure for the day. In caffeine studies, the dose was administered every 2 hours for 12 hours with a subtotal caloric expenditure increase of 8-11% [2]. However, this increase in caloric expenditure is limited as caffeine cannot be ingested throughout the night as a person sleeps, so this value, because it is limited to half of a day, does not continue throughout the night as ingestion stops [2]. This being the case, a person with an RMR of 1800 would see between a 70 – 110 increase in daily calorie expenditure; this value would be different depending on greater or lower RMR values between people. According to this research, it is safe to assume caffeine increases metabolic rate by 70-110 calories per 24 hour period if consumed every 2-3 hours, depending on the individual’s size, weight, and body composition [2].

Another study also showed the effect of caffeine in doses 4mg/kg and 8mg/kg led to an increase in RMR of 12 and 16%, respectively, for 3 hours post ingestion [3]. This means that more caffeine may bring about more stimulatory effects on metabolism and would lead to greater increase in calorie expenditure. Intaking the higher end of caffeine would lead to absolute numbers of 5,6-800mg of caffeine per day for a slight increase (~50-100 calories) in caloric expenditure. So, we ask ourselves the three questions to answer the overall question accurately:

Does caffeine work as a thermogenic? Yes.
How well does caffeine increase caloric expenditure, per day? 70-110 calories, possibly a bit more.
How much caffeine for that caloric expenditure increase? 100mg every 2-3 hours, much more for increased potency.


Capsaicin is a molecule found in many spicy foods that people believe leads to an increase in metabolism. However, not everyone eats spicy foods, so there is an alternative version that does not come with the heat, but with the same punch of traditional capsaicin called capsiate. When it comes to the research, things get extremely confusing. It seems that although there are some studies that show increases in energy expenditure with the intake of either molecule (capsaicin or capsiate), there are also studies showing no effect, as well as one study showing reduced energy expenditure [4]. It seems that the prevailing theory is body composition plays an important factor in effectiveness – apparently, lean individuals see a more pronounced benefit from these molecules than overweight or obese individuals [4]. However, another problem arises as even in those where capsiate is shown to be effective (0.8 – 0.9 calories/kg/day), that effect seems to diminish rapidly with continued ingestion [4]. This being the case, it seems that the body adapts quickly to the molecule rendering its caloric expenditure benefits moot in the long term. So, all in all, with so many scattered results, we cannot present a strong case that either capsaicin or capsiate offer a long term, significant thermogenic effect.

Does capsaicin/capsiate work as a thermogenic? Not conclusively.
How well does capsaicin/capsiate increase caloric expenditure, if any? None, conclusively.
How much capsaicin/capsiate is needed for caloric expenditure increase? Dose ranges from 3mg/day – 135mg/day, adding to its inconclusive nature.


Ephedrine is a component of an herb called ephedra and while you may be familiar with it stacked together with other products, we will first examine it on its own. Probably unsurprising, considering its potency, ephedrine is also effective in isolation. While getting concrete numbers is hard to come by as there are few studies that have directly looked at metabolism/caloric increase with ephedrine alone, we can still see it does have an impact on increasing metabolic capacity. According to a study done on adolescents, metabolism increased by about 5-7%, which is a sizeable jump by comparison to other popular stimulants like caffeine (discussed earlier)[5][6]. Numerically, another study conducted on a limited sample size of overweight women showed a weight reduction of 5.5 lbs after 4 weeks and 12.1 lbs after 12 weeks with three 20mg doses administered orally [7]. So, while it might be possible, between both of these studies, to extrapolate and find an estimated increase in caloric expenditure, it might lead us to shaky numbers. What we do know is ephedrine does work on its own if people are responsive to it [5].

Does ephedrine work as a thermogenic? Yes.
How well does ephedrine increase caloric expenditure, if any? No specific answer possible based on the available research.

How much ephedrine is needed for caloric expenditure increase? Proven, 20 mg 3x a day, other doses could also work as well, or better.

Ephedrine, Caffeine, & Aspirin (ECA Stack)

Now we are getting into the various stacks that people can take and often do take, because, frankly, they are more potent than any of these substituents in isolation. In this case, there are several studies substantiating the efficacy of ephedrine compounded with caffeine [8][9]. Now to find out how much better this stack is, say, compared to caffeine alone or ephedrine alone. An ephedrine and caffeine combination with 20mg of ephedrine and 200mg of caffeine has shown to increase metabolism by 30 calories every 3 hours [8]. So, if we ingest this EC stack 4 times in a day, for 12 hours, we will see, roughly, a 120 calorie increase in metabolism.

In a study examining ephedrine given at a 30mg dose along with simply an aspirin given at a 300mg dose, the results showed an increase of roughly .23 calories/min, which equates to 41 calories over 3 hours, and if we assume a person were to consume this stack 3-4 times, we get about a 120 - 160 calorie/day increase [10]. However, in the same study it was assumed that aspirin increased the effect of thermogenesis started by ephedrine only in obese individuals, not lean individuals. Other studies have also proven that an ECA stack taken at similar doses tends to be effective at increasing thermogenesis showing 7.5 lbs more weight loss, over 24 weeks, when taking ECA over those not taking ECA [13]. Yet other studies showed direct weight loss results and thermogenic potentials of ECA [11][12].

Does an ECA stack work as thermogenic? Yes.
How well does ephedrine increase caloric expenditure, if any? 120 – 160 calories/day
How much ephedrine is needed for caloric expenditure increase? 20 – 30mg ephedrine, 200mg of caffeine, ~300mg of aspirin, 3-4x a day, every 3 hours.

Are thermogenics safe? Side effects?

We have only touched on a few popular ingredients used in thermogenic supplements, so to say that all thermogenics are safe is a stretch – some are not, and usually for good reason as thermogenics increase energy output in one way or another, and some can certainly increase energy output via substantial body heat which can be unsafe. However, of the ones we have discussed, if you are healthy, the chances of serious adverse effects are rather low [6]. Caffeine, depending on sensitivity, will, at most, make you jittery and reduce sleep. Capsaicin is eaten regularly in spicy peppers and you likely will not drop dead from ingesting equal amounts, especially as the effect diminishes with time and consistent intake. Finally, ephedrine, while there are some inconclusive studies that show ephedrine increasing systolic blood pressure sharply, the body seems to address this via regulatory mechanisms quite quickly [14]. Other than that, ephedrine has been assumed safe for healthy populations, although caution and taking smaller doses would be advised until sensitivity is discovered [6].


Many thermogenics are bogus, because either they do not use proven ingredients or they do not use a suitable dosage. However, if a thermogenic were to use caffeine around doses of 100mg or higher, 3-4x a day, one would see a small increase (70-100) in daily calorie expenditure. Capsaicin offers little hope in terms of sustained weight loss, and ephedrine has too few studies on its individual impact on exact calorie expenditure. However, a combination of ephedrine and caffeine, a common combination, leads to superior results with possible increased calorie expenditure between 120-160 calories per day with 20-30mg ephedrine and 200mg caffeine, 3-4x a day.

Writer: Nicolas Verhoeven
This is educational material only and not meant to be prescripton, consult your physician before making any changes.


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[10] Horton, T. J. (1991). Aspirin potentiates the effect of ephedrine on the thermogenic response to a meal in obese but not lean women. International Journal for Obesity, 15(5), 359-366. Retrieved from

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[12] Horton, T. J. (1996). Post-prandial thermogenesis with ephedrine, caffeine and aspirin in lean, pre-disposed obese and obese women. International Journal for Obesity Related Metabolic Disorders, 20(2), 91-97. Retrieved from

[13] Astrup, A., Breum, L., & Toubro, S. (1995). Pharmacological and Clinical Studies of Ephedrine and Other Thermogenic Agonists. Obesity Research, 3(S4), 537S-540S.

[14] Persky, A. M., Berry, N. S., Pollack, G. M., & Brouwer, K. L. (2004). Modelling the cardiovascular effects of ephedrine. British Journal of Clinical Pharmacology, 57(5), 552-562. Retrieved from

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