Bitter Orange
Summary
Bitter orange is a safety-first page. A 2022 meta-analysis of 18 placebo-controlled trials (341 people) found no significant weight loss, while longer use raised blood pressure about 6/4 mmHg. Heart attacks, strokes and arrhythmias have been reported with bitter orange products, mostly multi-stimulant blends. In FDA testing, 6 of 59 products contained a synthetic stimulant not permitted in supplements.
Key facts
- Peel or fruit extract of Citrus aurantium, standardized to p-synephrine; structurally related to ephedrine but with different pharmacology[1][2]
- Weight loss: no significant effect (C); blood pressure: raised with prolonged use (C); fat burning during exercise: higher in two small lab studies (D)[3][7][8]
- Case reports of heart attack, stroke and arrhythmia with bitter orange products; NCAA lists synephrine as a banned stimulant[1][2][9][10][11]
- In an FDA analysis of 59 products, only 5 of 23 with a synephrine claim were within 80–120% of the label[12][1]
- None set; bitter orange is a botanical, not a nutrient[1]
- 6 graded human outcomes on this page
- October 10, 2026
How it works
Proposedp-Synephrine is a protoalkaloid that acts on adrenergic receptors and may mimic adrenaline and noradrenaline, which is the basis for claims of higher energy expenditure, fat breakdown and appetite suppression. How strongly it raises heart rate and blood pressure in people is disputed: some studies find increases and others do not.[2][1][3]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Cardiovascular safety | Grade C | Worsened | Meta-analysis of 11 trials · n = 222 · 2022 | 2 rows |
| Weight | Grade C | No effect | Meta-analysis · n = 94 · 2022 | 2 rows |
| Exercise metabolism | Grade D | Improved | Crossover RCT · n = 15 · 2021 | 2 rows |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Blood pressure and heart rate (harm) | Worsened | Grade C | Meta-analysis · n = 222 · 2022 Adults in 11 placebo-controlled trials Form: Bitter orange extract or p-synephrine · Dose: 10–214 mg p-synephrine · Duration: Single doses to prolonged use After prolonged use, systolic blood pressure rose 6.37 mmHg and diastolic 4.33 mmHg versus placebo; the authors conclude synephrine tends to raise blood pressure and heart rate. | 36235672 (opens PubMed)Source [3] |
| Body weight and body composition | No effect | Grade C | Meta-analysis · n = 94 · 2022 Adults in the weight-loss subset of placebo-controlled synephrine trials Form: Bitter orange extract or p-synephrine · Dose: 10–54 mg/day p-synephrine · Duration: Prolonged use (weeks) Weight loss with synephrine was not significant after prolonged treatment, and body composition did not change. | 36235672 (opens PubMed)Source [3] |
| Weight loss in randomized trials | No effect | Grade D | Systematic review · n = 20 · 2004 Adults with overweight in the only eligible RCT Form: Combination product containing bitter orange · Dose: Not stated in the review abstract · Duration: 6 weeks Only one eligible placebo-controlled trial was found, and it showed no statistically significant benefit for weight loss. | 15541270 (opens PubMed)Source [4] |
| Heart rate, blood pressure and ECG over 15 days | No effect | Grade D | Crossover RCT · n = 16 · 2018 Healthy adults Form: Bitter orange extract · Dose: 49 mg/day p-synephrine · Duration: 15 days No significant changes in heart rate, ECG, systolic or diastolic pressure, blood counts or chemistries, and no adverse effects reported. | 29130542 (opens PubMed)Source [6] |
| Fat oxidation, energy expenditure and heart rate in a maximal cycling test | Improved | Grade D | Crossover RCT · n = 15 · 2021 Elite cyclists Form: p-Synephrine · Dose: 3 mg/kg, single dose · Duration: Single dose Fat oxidation rate rose versus placebo; energy expenditure and heart rate during exercise did not change. | 32859142 (opens PubMed)Source [8] |
| Fat oxidation and energy expenditure during 1 hour of cycling | Improved | Grade D | Crossover RCT · n = 14 · 2020 Healthy adults Form: p-Synephrine · Dose: 3 mg/kg, single dose · Duration: Single dose Whole-body fat oxidation rose versus placebo while energy expenditure did not change. | 31691018 (opens PubMed)Source [7] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Bitter orange peel extract standardized to p-synephrine | Varies[6][3][13] | No human absorption data in our sources.[13] | No changes in heart rate or blood pressure at 49 mg/day for 15 days in one small trial; a 2022 meta-analysis found blood pressure rises with longer use.[6][3] | Cardiovascular-safety and weight trials (10–214 mg synephrine) |
| p-Synephrine (isolated) | Varies[7][8] | No human absorption data in our sources.[7] | Single 3 mg/kg doses did not change exercise heart rate in two small lab studies.[7][8] | Exercise fat-oxidation studies (3 mg/kg) |
| Multi-ingredient fat burners and pre-workouts containing bitter orange | Varies[1][2] | Usually combined with caffeine and other stimulants.[2] | Most serious adverse event reports involve these combination products.[1][2] | Most weight-loss trials and case reports |
Studied doses
Doses studied in human trials ranged from 10 to 214 mg/day of p-synephrine, from single doses to about 8 weeks. A single 54 mg dose raised heart rate and blood pressure for up to 5 hours in one study, while other trials at 20–49 mg/day found no change.[3][2][6]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Medicines
Who should be careful
- Heart disease, high blood pressure or arrhythmia
- Bitter orange products have been linked to heart attacks, strokes and dangerous heart rhythms, and synephrine raised blood pressure with prolonged use in pooled trials.[1][3]
- Pregnancy and breastfeeding
- NCCIH says it may not be safe, and animal data suggest it might reduce milk production.[1]
- Competitive athletes
- The NCAA lists synephrine (bitter orange) as a banned stimulant.[1]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Cardiovascular safety
Serious heart and stroke events have been reported, and whether bitter orange itself or co-ingredients are to blame is unresolved.
- Case reports
- Published cases include a lateral-wall heart attack in a 55-year-old after a year of a bitter orange weight-loss product, an ST-elevation heart attack in a healthy 24-year-old within hours of a synephrine product, and supraventricular tachycardia with heart-muscle injury in a 38-year-old woman.[9][10][11]
- Conflicting trials
- A single 54 mg dose raised heart rate and blood pressure for up to 5 hours in 15 adults, while an 8-week trial of a 20 mg/day product found no change; pooled data show blood pressure rises with longer use.[2][3]
- Industry-linked reassurance
- Two small crossover trials at 49 mg/day found no heart-rate, blood-pressure or ECG changes, and a 2017 review concluded bitter orange is safe at common doses; both involve an author who has consulted for a bitter orange extract company.[5][6][13]
- Exercise
- A 180 mg synephrine dose before submaximal exercise showed no unfavorable heart-rate or blood-pressure effects in 12 healthy men.[14]
How to read the label
- Label dose vs clinical doseLabels typically list mg of bitter orange extract or "synephrine". Trials used 10–214 mg of p-synephrine, and FDA testing found most labels inaccurate.[3][12]
- Illegal synthetic aminesFDA researchers found methylsynephrine (up to 240 mg per daily serving) in 6 products and isopropyloctopamine in 1; neither is permitted in supplements.[12][1]
- Check the full stimulant loadAdd up caffeine from all sources; many bitter orange products include several hundred milligrams of caffeine.[2]
Frequently asked questions
Does bitter orange help you lose weight?
No: a 2022 meta-analysis of placebo-controlled trials found no significant weight loss or change in body composition.[3]
Is bitter orange safe?
It is a safety concern. Heart attacks, strokes and arrhythmias have been reported with bitter orange products, and synephrine raised blood pressure with prolonged use in pooled trials.[1][3]
Is synephrine the same as ephedrine?
No. They are structurally similar but have different pharmacology; bitter orange became popular as an ephedra substitute after the 2004 FDA ban.[1][2]
Can athletes use bitter orange?
The NCAA lists synephrine (bitter orange) as a banned stimulant.[1]
Can I take bitter orange with caffeine?
Most serious adverse reports involve products combining synephrine with caffeine or other stimulants, so this combination is the one to avoid.[2][12]
Is eating bitter orange or marmalade a problem?
NCCIH considers bitter orange likely safe in amounts commonly found in foods; the concerns are about concentrated supplements.[1]
Sources
- [1]Bitter Orange: Usefulness and Safety (last updated November 2024). NIH National Center for Complementary and Integrative Health, 2024. fact-sheet
- [2]Dietary Supplements for Weight Loss: Fact Sheet for Health Professionals (updated May 18, 2022). NIH Office of Dietary Supplements, 2022. fact-sheet
- [3]The Safety and Efficacy of Citrus aurantium (Bitter Orange) Extracts and p-Synephrine: A Systematic Review and Meta-Analysis.. Nutrients, 2022. meta-analysis
- [4]Safety and efficacy of citrus aurantium for weight loss.. Am J Cardiol, 2004. systematic-review
- [5]Cardiovascular Safety of Oral p-Synephrine (Bitter Orange) in Healthy Subjects: A Randomized Placebo-Controlled Cross-over Clinical Trial.. Phytother Res, 2016. crossover-RCT
- [6]Safety evaluation of p-synephrine following 15 days of oral administration to healthy subjects: A clinical study.. Phytother Res, 2018. crossover-RCT
- [7]Acute p-synephrine ingestion increases whole-body fat oxidation during 1-h of cycling at Fatmax.. Eur J Nutr, 2020. crossover-RCT
- [8]p-Synephrine, the main protoalkaloid of Citrus aurantium, raises fat oxidation during exercise in elite cyclists.. Eur J Sport Sci, 2021. crossover-RCT
- [9]Possible association of acute lateral-wall myocardial infarction and bitter orange supplement.. Ann Pharmacother, 2004. observational
- [10]STEMI in a 24-year-old man after use of a synephrine-containing dietary supplement: a case report and review of the literature.. Tex Heart Inst J, 2009. observational
- [11]Unexplained Supraventricular Tachycardia and Myocardial Injury After Bitter Orange Supplement Use in a Young Woman.. JACC Case Rep, 2026. observational
- [12]Analysis of bitter orange dietary supplements for natural and synthetic phenethylamines by LC-MS/MS.. Drug Test Anal, 2020. observational
- [13]Safety, Efficacy, and Mechanistic Studies Regarding Citrus aurantium (Bitter Orange) Extract and p-Synephrine.. Phytother Res, 2017. review
- [14]Bitter Orange (Citrus aurantium L.) Intake Before Submaximal Aerobic Exercise Is Safe for Cardiovascular and Autonomic Systems in Healthy Males: A Randomized Trial.. Front Nutr, 2022. crossover-RCT
What changed
- First draft. Every PMID checked against NCBI E-utilities esummary (title and year taken from the record) and abstracts read for the cited rows.
- Adversarial review pass: every evidence row re-read against its PubMed abstract; the 2022 meta-analysis participant counts (341 overall, 222 for blood pressure, 94 for weight) taken from PMC9572433. Industry ties: S. Stohs consultancy for Novel Ingredients (PMC5655712) disclosed on the 15-day safety trial and the 2017 review. NCCIH fact sheet (opened 2026-10-10, updated November 2024) and NIH ODS weight-loss fact sheet (opened 2026-10-10, updated May 18, 2022) used for safety, regulatory and product-quality statements. Retraction, expression-of-concern and erratum check run on all 12 PMIDs: none flagged. Safety-first page: no cost-per-dose block and no product links at launch. Page set indexable.