Synephrine: What Is It?

What is Synephrine?

Synephrine is a stimulant that is chemically similar to ephedrine. Today, a popular claim associated with this supplement is that it promotes weight loss. Many dietary supplement companies have begun to replace the banned ephedrine with synephrine.

Where does it come from?

Synephrine is derived from a fruit tree known as Citrus aurantium. The Citrus aurantium tree is native to Vietnam, but is cultivated all over the world. Synephrine is made from the unripe fruit of the tree. Unlike the sweet tasting fruit that comes from most citrus plants, the fruit from this plant is described as bitter. It is more commonly known as bitter orange, Seville orange, sour orange, and zhi shi. In traditional Chinese medicine, zhi shi was used to treat abdominal pains and gastrointestinal problems.

The extract from this fruit contains five alkaloids: synephrine, N-methyl-tyramine, hordnine, octopamine, and tyramine. The most abundant of these is synephrine. There are six different isomers of synephrine. However, is it unclear exactly which one is in the Citrus aurantium. Most research indicates that it is either para-synephrine or meta-synephrine.

How does it work?

Synephrine stimulates the sympathetic nervous system, which is activated during excitement or stress. This branch of the nervous system increases heart rate as opposed to the parasympathetic nervous system which decreases heart rate.

At the cellular level, synephrine acts on different receptors through the release of norepinephrine and epinephrine. There are five different classes of receptors: alpha 1, alpha 2, beta 1, beta 2, and beta 3. Although there is ongoing research to confirm exactly which of the receptors synephrine acts upon, most data indicates effects on beta 3 and limited effects on beta 2 and alpha 2.

The beta 3 receptor increases the rate of fat release from body stores, which is known as lipolysis, and increases the resting metabolic rate, which is known as thermogenesis. Research also shows synephrine has limited affects on beta 2 and alpha 2 receptors. The beta 2 receptor is located in heart muscle. It influences heart function and causes dilation of blood vessels in the heart. The alpha 2 receptor is located in adipose tissue and can inhibit lipolysis.

Synephrine is thought to be a safer supplement than ephedrine because of its actions on the receptors. Limited effects on the beta 2 receptors indicates that synephrine should not cause as many heart problems as ephedrine and the limited effect on alpha 2 indicates that the effects of beta 3 will not be inhibited.

Synephrine vs. Ephedrine

After the ban of ephedrine, dietary supplement companies needed a new stimulant to use as an ingredient. Synephrine and ephedrine were found to be chemically similar with similar effects as well. Many companies found synephrine to have the same stimulant properties without some of the harmful side effects ephedrine was argued to have, such as the cause of cardiovascular problems, respiratory problems, and nervous system problems. Continuing research shows that synephrine may be more thermogenic and less stimulatory than ephedrine due to the differences in effects on the beta and alpha receptors. However, there is still a debate as to how safe and effective synephrine really is.


There have been many claims made about synephrine, such as it increases metabolic rate, increases caloric expenditure, burns fat, promotes weight loss, and increases energy levels. However, many of these claims made are not based on scientific research, but only thoughts as to what may be an effect. Most of the research has been performed on animals and not on humans, which makes the claims less valid.

One research study recorded synephrine and octopamine increasing the metabolic rate and decreasing the amount of brown adipose tissue in dogs. However, adult humans do not have brown adipose tissue, so this research has no significance for humans.

Another study used mice as subjects. The mice were given different doses of synephrine to test the effects of the supplement on the sympathetic nervous system. The mice that were given the highest doses had a reduction of water and food intake and experienced weight loss. However, there was also a 50% death rate. In doses given to the mice similar to that recommended for humans, there was a slight weight loss found, but there was also a 10% death rate.


Synephrine has been showed to be somewhat effective when it is combined with another stimulant, such as caffeine. Other research shows that with a healthy diet and regular exercise, a dietary supplement containing synephrine can aid in weight loss. However, the weight loss is minimal.

Synephrine is thought to have some of the same side effects as ephedrine, but to a lesser degree. It could cause cardiac problems and high blood pressure, but there have been no major complaints with consumers.

What is it used in?

Synephrine has been used in nasal spray for decades. It is found in over-the-counter medications for such aliments as colds, the flu, and allergies. It is also used in ophthalmic solutions to dilate the eye prior to an exam or surgery. Today, with new claims coming out about its weight loss potential, it is commonly found in several dietary supplements.


Even though synephrine is becoming a widely used supplement, there is still not enough research to support the weight loss claims. Different research studies show contradictory results on the effectiveness and different studies support different claims. Overall, synephrine appears to be safer than ephedrine and perhaps somewhat effective, but until more research is done, these claims cannot be confirmed.