Synephrine (Phenylethylamine Alkaloid · Thermogenic · Beta-3 Adrenergic)

Compound	Synephrine (p-Synephrine)
Chemical class	Alkaloid — Phenylethylamine (Protoalkaloid)
CAS	94-07-5
Primary source	Citrus aurantium (bitter orange peel), Citrus sinensis (sweet orange)
Key applications	Thermogenic, fat mobilisation, athletic performance, adrenergic
Claim strength	Moderate
Typical form	Bitter orange extract standardised to synephrine; isolated synephrine HCl
Buy from Herbuno	Request availability and bulk pricing →

Commercial source: p-Synephrine is commercially available as a standardised constituent of bitter orange (Citrus aurantium) peel extract from specialist botanical suppliers. Isolated synephrine HCl is available from specialist chemical suppliers. Contact Herbuno for availability assessment. Traditional use: Bitter orange (Zhi Shi in TCM, immature fruit; Zhi Ke, ripe fruit) has been used in Chinese traditional medicine for over 2,000 years for digestive complaints, constipation, gastroparesis, and as a Qi-moving herb. Synephrine’s adrenergic properties were not specifically targeted in traditional use; the herb was used for its overall digestive and circulatory-stimulating effects. Research trajectory: p-Synephrine emerged as a safer ephedrine alternative following the FDA ban of ephedra-containing supplements in 2004. Structurally similar to ephedrine but with different receptor selectivity, synephrine acts primarily on beta-3 adrenergic receptors (peripheral fat mobilisation) rather than beta-1/beta-2 (cardiovascular stimulation). Multiple human studies have been conducted for thermogenic, fat loss, and athletic performance applications. See sourcing options below.

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Evidence for Synephrine Applications

Thermogenic and metabolic rate: Human RCTs demonstrate synephrine (50–100 mg) increases resting metabolic rate by 2.5–4.5% compared to placebo. The beta-3 adrenergic mechanism activates thermogenesis in adipose tissue and skeletal muscle without significant beta-1/beta-2 cardiovascular stimulation at supplement doses. Claim strength: Moderate.

Athletic performance: Small human studies show synephrine (50–100 mg) pre-exercise improves upper and lower body muscular strength and power output. The mechanism involves beta-3 adrenoceptor-mediated catecholamine sensitisation. Effect sizes are modest compared to caffeine. Claim strength: Moderate.

Fat mobilisation (combined with caffeine and naringenin): The bitter orange alkaloid-flavonoid complex (synephrine + naringenin) has greater fat mobilisation in human adipose microdialysis studies than either compound alone, suggesting synergy. The combination is commercially established in thermogenic supplement formulations. Claim strength: Moderate.

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Dosage & Formulator Specification

Clinical dose range: 50–100 mg p-synephrine per serving for thermogenic applications. Bitter orange extract standardised to 6% or 30% synephrine is the standard commercial form. A 6% bitter orange extract at 500 mg/serving delivers 30 mg synephrine; a 30% extract at 200 mg delivers 60 mg synephrine.

Regulatory note: p-Synephrine (from bitter orange) is distinct from m-synephrine (oxilofrine), which is a prohibited substance in sport (WADA). Most commercial bitter orange extracts contain p-synephrine; ensure HPLC specification confirms p-synephrine content and absence of m-synephrine. Some national supplement regulations have placed restrictions on synephrine content per serving (e.g., France limits bitter orange extract in supplements); verify current regulatory limits in your target market.

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Frequently Asked Questions — Synephrine

Is synephrine a safe replacement for ephedrine?
p-Synephrine has a different and more favourable cardiovascular safety profile than ephedrine at equivalent doses. Ephedrine acts on beta-1/beta-2 adrenoceptors (cardiac stimulation, hypertension, arrhythmia risk); synephrine acts primarily on beta-3 adrenoceptors (thermogenesis, fat mobilisation) with much weaker cardiovascular stimulant activity. Multiple human RCTs confirm p-synephrine does not significantly increase heart rate or blood pressure at effective thermogenic doses. It is not a direct pharmacological substitute for ephedrine but serves a similar thermogenic role with an improved safety profile.

Why was bitter orange extract promoted after the ephedra ban?
The FDA banned ephedra-containing supplements in 2004 following adverse cardiovascular events including deaths. The supplement industry sought a thermogenic replacement, and bitter orange extract (synephrine) was positioned as a natural, legally available alternative with similar thermogenic mechanisms but different receptor selectivity and improved safety. This commercial positioning has driven the majority of the synephrine research evidence base.

Is there concern about synephrine and cardiovascular safety?
At doses of 50–100 mg p-synephrine, multiple human RCTs show no significant increase in heart rate or blood pressure versus placebo. However, high-dose synephrine (>200 mg) or synephrine combined with caffeine at high doses produces additive cardiovascular stimulation that warrants caution. Standard advisory language for cardiovascular conditions and caffeine co-administration is appropriate. Athletes should note that sports bodies may test for synephrine depending on the sport.

Does bitter orange extract also contain other adrenergic alkaloids?
Yes. Bitter orange peel contains a complex alkaloid fraction including p-synephrine (dominant), N-methyltyramine, hordenine (also an adrenergic alkaloid), octopamine, and tyramine. The combined adrenergic alkaloid profile of whole bitter orange extract produces broader adrenergic stimulation than isolated p-synephrine alone. For precise synephrine dosing, isolated p-synephrine HCl is more appropriate; for broad-spectrum bitter orange extract activity, the whole alkaloid complex from standardised extract delivers the full phytochemical complement.

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Claim-strength scale – High = multiple human RCTs; Moderate = limited trials or strong preclinical convergence; Emerging = early-stage lab or animal data.

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