Three studies reported increased metabolic rates when ingesting Citrus aurantium products.
– J Med. 2002;33(1-4):247-64. — Citrus aurantium as a thermogenic, weight-reduction replacement for ephedra: an overview. — Preuss HG, DiFerdinando D, Bagchi M, Bagchi D.

Bitter orange or synephrine, found in bitter orange, has been associated with adverse cardiovascular reactions. Based on the Naranjo probability scale, C. aurantium is possibly associated with this cardiovascular event.
– Ann Pharmacother. 2004 Mar 16 — Possible Association of Acute Lateral-Wall Myocardial Infarction and Bitter Orange Supplement (May). — Nykamp DL, Fackih MN, Compton AL.

Individuals with severe hypertension, tachyarrhythmias, and narrow-angle glaucoma and monoamine oxidase inhibitor recipients should avoid consumption. Persons taking decongestant-containing cold preparations should also refrain from intake.
– J Clin Pharmacol. 2001 Oct;41(10):1059-63. — Seville (sour) orange juice: synephrine content and cardiovascular effects in normotensive adults. — Penzak SR, Jann MW, Cold JA, Hon YY, Desai HD, Gurley BJ.

Bitter Orange may increase blood pressure and is considered a diuretic herb. There are also reports of it causing light sensitivity and skin irritation.

Bitter Orange can interact adversely with many types of prescription and over the counter medications. Do not use if you are pregnant
or breastfeeding and do not give to children.

Describes a patient in whom ischemic colitis developed one week after taking a weight-loss supplement. The patient had no other predisposing factors, and discontinuation of the supplement led to improvement and resolution of the symptoms.

– Mayo Clin Proc. 2006 Dec;81(12):1630-1. — Ischemic colitis associated with use of a bitter orange-containing dietary weight-loss supplement.Sultan S, Spector J, Mitchell RM.

To examine the safety and efficacy of citrus aurantium, an herb now commonly used as a substitute for ephedra in dietary supplements marketed to promote weight loss, a systematic review was conducted. An extensive search of MEDLINE, EMBASE, BIOSIS, and the Cochrane Collaboration Database identified only 1 eligible randomized placebo controlled trial, which followed 20 patients for 6 weeks, demonstrated no statistically significant benefit for weight loss, and provided limited information about the safety of the herb.

– Safety and efficacy of citrus aurantium for weight loss. — Bent S, Padula A, Neuhaus J. — Am J Cardiol. 2004 Nov 15;94(10):1359-61.

Seville orange (Citrus aurantium) extracts are being marketed as a safe alternative to ephedra in herbal weight-loss products, but C. aurantium may also have the potential to cause adverse health effects. C. aurantium contains synephrine (oxedrine), which is structurally similar to epinephrine. Synephrine increases blood pressure in humans and other species, and has the potential to increase cardiovascular events. Additionally, C. aurantium would be expected to increase serum levels of many drugs. There is little evidence that products containing C. aurantium are an effective aid to weight loss. Synephrine has lipolytic effects in human fat cells only at high doses, and octopamine does not have lipolytic effects in human adipocytes.
– Citrus aurantium, an ingredient of dietary supplements marketed for weight loss: current status of clinical and basic research. — Fugh-Berman A, Myers A. — Exp Biol Med (Maywood). 2004 Sep;229(8):698-704.