RESEARCH MONOGRAPH · KDC-MN-383

Synephrine

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 2 min read

Our opinion on this compound

53/100

Bitter orange alkaloid with weak adrenergic activity; mostly hype carried over from the ephedra ban

Honestly synephrine is a compound that exists because of regulatory accident more than pharmacology. When the FDA banned ephedra in 2004, the supplement industry needed a replacement adrenergic agent and bitter orange extract (Citrus aurantium) standardized for p-synephrine fit the bill. It's structurally similar to phenylephrine, primarily a beta-3 and weakly beta-2 adrenergic agonist with some alpha-1 activity, and the marketing pitch was always 'ephedrine without the side effects.'

The pharmacology actually justifies a more modest version of that pitch. Oral bioavailability of p-synephrine is poor and CNS penetration is minimal, which is why the cardiovascular signal at typical supplement doses (25 to 50 mg) is small. Blood pressure changes in controlled studies are usually nonsignificant or low single-digit mmHg. The thermogenic effect is also modest, measurable but small.

What we like: it's a reasonable beta-3 tool compound for adipocyte and brown fat work in vitro. The receptor pharmacology is decent, and the m-synephrine and p-synephrine isomers can be separated to ask receptor-selectivity questions.

What we don't like is how it gets marketed in the fat-burner space. The clinical thermogenic data is real but minor and gets dramatically oversold. The interaction risk with MAOIs and other adrenergic compounds is real and underappreciated. The Stohs reviews are funded by the bitter orange industry and read accordingly.

Sourcing is the messy part. Bitter orange extract varies wildly in standardization, the m-synephrine versus p-synephrine ratio matters pharmacologically and is rarely specified, and adulteration with synthetic phenylephrine has been documented. For research, the pure isolated p-synephrine reference standard from analytical suppliers is the only way to do this rigorously.

Honestly the more interesting use of synephrine is as a structural reference point for understanding the trace amine and adrenergic receptor families. It binds TAAR1 weakly, which puts it in conversation with octopamine and the trace amine literature, which is genuinely undervalued work.

Staying power is moderate, mostly because the supplement industry will keep using it whether or not the evidence justifies it.

Evidence: 45
Mechanism: 65
Reliability: 50
Safety: 65
Sourcing: 55
Value: 50
Signal: 40
Staying power: 55

Plain-language summary Intrigue 42 / 100

Synephrine is an alkaloid from bitter orange peel (Citrus aurantium) that became a bestselling thermogenic supplement after the FDA banned ephedra in 2004. Structurally it resembles phenylephrine, but it preferentially activates beta-3 adrenergic receptors over the alpha-1 and beta-1 receptors that drive blood pressure changes. The beta-3 activity stimulates fat oxidation and thermogenesis in adipose tissue, which is the basis of the weight-loss claims. Clinical evidence for actual fat loss is modest at best. Plasma half-life is about two hours. Used as a beta-3-preferring adrenergic agonist in metabolic research and as the workhorse stimulant ingredient in many over-the-counter weight-loss formulas. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Adrenergic agonist (bitter orange alkaloid)

p-Synephrine; a phenylethanolamine alkaloid from Citrus aurantium (bitter orange); a beta-3 adrenergic-preferring agonist used as a thermogenic supplement.

Abstract

Synephrine (p-synephrine, (R/S)-4-[1-hydroxy-2-(methylamino)ethyl]phenol; CAS 94-07-5; molecular formula C9H13NO2; molecular weight 167.21) is a phenylethanolamine alkaloid from Citrus aurantium (bitter orange) and other Citrus species. The compound is a structural analog of phenylephrine (the m-isomer) with a beta-3 adrenergic preference (relative to alpha-1 and beta-1) that distinguishes its pharmacology. The beta-3 activity drives thermogenesis and fat oxidation in adipose tissue, the basis for its supplement use as a weight-loss aid. Synephrine became prominent after the 2004 FDA ban on ephedra (which contained the more potent ephedrine). Clinical evidence for weight-loss effect is modest. Plasma half-life is approximately 2 hours. Used as a beta-3-preferring adrenergic agonist in metabolic research and supplement formulations.

Mechanism of action

Phenylethanolamine adrenergic agonist with beta-3 preference; thermogenesis and fat oxidation in adipose tissue.

Reported research dose ranges

Supplement 30 to 100 mg in the published literature.

References

Stohs SJ, et al. A review of the human clinical studies involving Citrus aurantium (bitter orange) extract and its primary protoalkaloid p-synephrine. Int J Med Sci 2012.
Haaz S, et al. Citrus aurantium and synephrine alkaloids in the treatment of overweight and obesity. Obes Rev 2006.
Stohs SJ, Shara M. A review of the safety and efficacy of synephrine. Phytother Res 2017.

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KDC-MN-383

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

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Synephrine

Abstract

Mechanism of action

Reported research dose ranges

References

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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