Synephrine Overview

Learn about one of the most commonly used ingredients in weight loss and diet supplements...

Synephrine is the main "active" compound found in the fruit of a plant called Citrus aurantium. The fruit is also known as zhi shi (in traditional Chinese medicine), and as green orange, sour orange and bitter orange in other parts of the world. Synephrine is chemically very similar to the ephedrine and pseudo-ephedrine found in many OTC cold/allergy medications and in a number of weight loss and energy supplements which contain Ma Huang. But synephrine differs from ephedrine in that synephrine is considered a semi-selective sympathomimetic (because it targets some tissues such as fat, more than it targets others such as the heart) versus a non-selective sympathomimetic (like ephedra which targets many tissues equally and thus often causes side effects). For example, although some high-dose ephedra-containing supplements have been associated with certain cardiovascular side effects as elevated blood pressure and heart palpitations, researchers at Mercer University in Atlanta have shown that Citrus aurantium extract (because it targets fat tissue rather than heart tissue) has no effect on hemodynamics such as heart rate and blood pressure.

Claims

• Increases metabolic rate
• Increases caloric expenditure
• Fat burner
• Promotes weight loss
• Increases energy levels

Theory

Because synephrine is a mild stimulant similar in some ways to caffeine and ephedrine, it is thought to have similar effects in terms of providing an energy boost, suppressing appetite, and increasing metabolic rate and caloric expenditure. In traditional Chinese medicine, zhi shi is used to help stimulate qi (pronounced chee, and defined as the body’s vital energy or life force) – but in order to maximize the metabolic benefits of these extracts, total synephrine intake should probably be kept to a range of 2-10 mg/day. Although synephrine and several other compounds found in zhi shi are structurally similar to ephedrine and are known to act as stimulants (via adrenergic activity), zhi shi does not appear to have the same negative central nervous effects of ma huang (ephedra). Through its stimulation of specific adrenergic receptors (beta-3, but not beta-1, beta-2 or alpha-1), zhi shi is theorized to stimulate fat metabolism without the negative cardiovascular side effects experienced by some people with Ma Huang (which stimulates all beta-adrenergic receptors).

Scientific Support

The effects of synephrine alone or in combination with other ingredients such as kola nut and guarana (both are caffeine sources) or with salicylates such as white willow (a natural form of aspirin) generally fall into the category of acting as a mild stimulant. The extract of citrus aurantium, in addition to synephrine, also contains tyramine and octopamine. Octopamine may be related in some way to appetite control, as it is thought to influence insect behavior by stopping bugs from eating the citrus fruit (so if you're an insect, this may be the perfect weight loss supplement for you).

A recent study conducted in dogs suggests that synephrine and octopamine can increase metabolic rate in a specific type of fat tissue known as brown adipose tissue (BAT). This effect would be expected to increase fat loss in humans – except for one small detail – adult humans don't have brown adipose tissue to speak of.

Up until very recently, synephrine-containing supplements existed with only some interesting theories on how they might work to increase metabolic rate and promote significant weight loss. At this writing, there are now at least two clinical studies showing that synephrine-containing supplements help promote weight loss, and at least three clinical studies showing an enhanced thermogenesis (calorie expenditure) from these supplements. There is a great deal of research currently underway into the weight loss benefits of synephrine and supplements with related thermogenic effects, leading researchers in the Department of Physiology at Georgetown University to conclude that “Citrus aurantium may be the best thermogenic substitute for ephedra.”

Safety

Early animal studies using high doses of isolated (purified) synephrine have been shown to raise blood pressure - but more recent human studies of citrus aurantoum extracts (standardized for synephrine) have not demonstrated any cardiovascular side effects. When used as directed (see dosage below), synephrine-containing supplements appear to be quite safe and should be treated as a mild stimulant (similar to a cup of coffee) with appetite controlling and mild thermogenic properties.

Value

The most likely explanation for weight loss effects attributed to citrus aurantium supplements is the mild appetite reduction and thermogenisis. Although these effect is likely to be somewhat less dramatic that effects induced by Ma Huang (ephedra alkaloids), users can expect variable effects including reduced appetite and heightened feelings of energy (similar to caffeine) – both of which are likely to result in weight loss - but with less chance of cardiovascular involvement (palpitations, blood pressure, heart rate, etc).

Dosage

Because synephrine is but one small component of the Citrus aurantium fruit, a standardized extract is recommended. A dose of 4-20 mg of synephrine per day is a typical dose found in products providing 200-600 mg of a standardized citrus aurantium extract (3-6% synephrine).