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Bitter orange

Supplement botanical fitnessenergy
Aka: Citrus aurantium, synephrine
Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.
How to use
What it’s for
Energy expenditure may rise; weight effects inconclusive
Take with
Nothing established — trials used multi-ingredient products
Studied for
Trials ran 6–8 weeks
Pros & cons
Pros
  • A 2012 review of 23 studies: resting metabolic rate up
  • NCCIH: likely safe in amounts commonly found in foods
Cons
  • NCCIH: not clearly shown helpful for any health purpose
  • Abnormal heart rhythms, heart attacks, strokes reported
  • Became the ephedra substitute after the 2004 FDA ban
Sources
  1. NIH ODS — Dietary Supplements for Weight Loss (Health Professional), summary table row for bitter orange (read via the archive.org capture; ods.od.nih.gov returns 403 to a direct fetch) · read 2026-08-27
    what it says
    “Bitter orange (Citrus aurantium L.) … Small clinical trials of poor methodological quality … Possible increase in resting metabolic rate and energy expenditure; inconclusive effects on weight loss … Chest pain, anxiety, headache, musculoskeletal complaints, and increased blood pressure and heart rate”
  2. NIH ODS — Dietary Supplements for Weight Loss (Health Professional), bitter orange efficacy, 2012 review and 2011 systematic review (read via the archive.org capture; ods.od.nih.gov returns 403 to a direct fetch) · read 2026-08-27
    what it says
    “The authors of a 2012 review of 23 small human clinical studies involving a total of 360 participants concluded that synephrine increases resting metabolic rate and energy expenditure”
  3. NIH ODS — Dietary Supplements for Weight Loss (Health Professional), bitter orange efficacy, confounding by combination products (read via the archive.org capture; ods.od.nih.gov returns 403 to a direct fetch) · read 2026-08-27
    what it says
    “Interpreting the results of these studies is complicated by the fact that bitter orange is almost always combined with other ingredients in weight-loss supplements.”
  4. NIH ODS — Dietary Supplements for Weight Loss (Health Professional), bitter orange safety, single-dose haemodynamic study (read via the archive.org capture; ods.od.nih.gov returns 403 to a direct fetch) · read 2026-08-27
    what it says
    “a single dose of 900 mg bitter orange standardized to 6% (54 mg) synephrine significantly increased heart rate as well as systolic and diastolic blood pressure for up to 5 hours compared to placebo”
  5. NIH ODS — Dietary Supplements for Weight Loss (Health Professional), bitter orange, ephedra substitution (read via the archive.org capture; ods.od.nih.gov returns 403 to a direct fetch) · read 2026-08-27
    what it says
    “After FDA banned the use of ephedrine alkaloids in dietary supplements in 2004 … manufacturers replaced ephedra with bitter orange in many products; thus, bitter orange became known as an ephedra substitute”
  6. NIH ODS — Dietary Supplements for Weight Loss (Health Professional), Interactions with medications section (read via the archive.org capture; ods.od.nih.gov returns 403 to a direct fetch) · read 2026-08-27
    what it says
    “caffeine and bitter orange, could have an additive effect if taken with other stimulants. Bitter orange has also been shown to inhibit CYP3A4 activity, leading to increased blood levels of certain drugs, such as cyclosporine and saquinavir”
  7. NIH ODS — Dietary Supplements for Weight Loss (Health Professional), caffeine safety section (read via the archive.org capture; ods.od.nih.gov returns 403 to a direct fetch) · read 2026-08-27
    what it says
    “Combining caffeine with other stimulants, such as bitter orange and ephedrine, can potentiate these adverse effects.”
  8. NCCIH — Bitter Orange (What the Science Says / effectiveness) · read 2026-08-27
    what it says
    “Bitter orange has not been clearly shown to be helpful for any health-related purpose.”
  9. NCCIH — Bitter Orange (Safety: reported serious events and cardiovascular evidence) · read 2026-08-27
    what it says
    “Cases of serious medical events, including abnormal heart rhythms, heart attacks, and strokes, have been reported … Some studies indicate that bitter orange raises blood pressure and heart rate, but others do not.”
  10. NCCIH — Bitter Orange (Safety: food amounts) · read 2026-08-27
    what it says
    “Bitter orange is likely safe when used orally in amounts commonly found in foods.”
  11. NCCIH — Bitter Orange (Safety: medicines) · read 2026-08-27
    what it says
    “If you take any type of medicine, talk with your health care provider before using bitter orange or other herbal products; some herbs and medicines interact in harmful ways.”
  12. HSA — Guidelines on Prohibited and Restricted Ingredients in Health Supplements and Traditional Medicines, GL-CHPB-1-012 Rev. No. 001 (Oct 2025) — Annex A (118 substances, prohibited/restricted) and Annex B (4 substances: caffeine, Camellia sinensis extract, Hypericum perforatum, L-tryptophan) both read in full: bitter orange / Citrus aurantium / synephrine is NOT LISTED in Annex A or Annex B · read 2026-08-27
    what it says
    “The objective of this guideline is to highlight the substances of concern when used in HS and TM and is not meant to be an exhaustive list.”
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Updated 2026-08-29. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.