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12 peer-reviewed studies
What the evidence says
Most Synephrine studies are mechanism or observational rather than RCTs that measure a clinical effect — keep findings provisional.
Most evidence is from high-quality meta-analyses and randomised trials published 2004–2022.
Based on 12 studies · 2 meta-analyses · 6 RCTs
Confidence
HighBy outcome
3 studies in the last 5 years · Latest meta-analysis: 2022
A meta-analysis of Citrus aurantium (bitter orange) / p-synephrine found small metabolic effects and concluded it modestly raises metabolic rate without large blood-pressure changes at typical doses, while urging caution with stimulant combinations.
Koncz D et al. · Nutrients (2022)
An early meta-analysis on citrus aurantium for weight loss found insufficient evidence of meaningful efficacy and flagged cardiovascular safety questions.
Bent S et al. · The American journal of cardiology (2004)
An evidence-based systematic review of bitter orange summarized modest thermogenic effects and a generally tolerable profile at low p-synephrine doses.
Ulbricht C et al. · Journal of dietary supplements (2013)
A randomized trial showed p-synephrine raises fat oxidation.
Gutiérrez-Hellín J et al. · European journal of sport science (2021)
A review of published adverse-event reports examined bitter orange extract and p-synephrine safety.
Stohs SJ et al. · Journal of dietary supplements (2020)
A randomized trial found p-synephrine increased fat oxidation during graded exercise.
Gutiérrez-Hellín J et al. · Nutrients (2022)
A randomized trial examined p-synephrine and caffeine on substrate oxidation during exercise.
Gutiérrez-Hellín J et al. · Medicine and science in sports and exercise (2018)
Acute p-synephrine ingestion increased fat oxidation rate during exercise.
Gutiérrez-Hellín J et al. · British journal of clinical pharmacology (2016)
Acute p-synephrine ingestion increased whole-body fat oxidation during exercise.
Gutiérrez-Hellín J et al. · European journal of nutrition (2020)
A citrus aurantium + caffeine complex was tested against placebo on metabolic biomarkers.
Kliszczewicz B et al. · Journal of the International Society of Sports Nutrition (2019)
A safety review of Citrus aurantium and its primary protoalkaloid p-synephrine summarized cardiovascular considerations.
Stohs SJ et al. · Phytotherapy research : PTR (2011)
An early clinical study assessed citrus aurantium and synephrine alkaloids for overweight management.
Haaz S et al. · Obesity reviews : an official journal of the International Association for the Study of Obesity (2006)