Allium cepa

Onion/Drug Interactions:

  • AllantoinAllantoin: Based on clinical trial, cepae extract from onions, heparin, and allantoin may improve healing of injuries incurred during laser tattoo removal or surgery (139; 140; 141; 142; 143; 144).
  • AllopurinolAllopurinol: Oral onion administration reduced uric acid levels in hyperuricemic rats (312). These effects were less potent than allopurinol; however, the hypouricemic effect may be due to different mechanism than allopurinol and may be a useful addition to minimize adverse effects of allopurinol.
  • AntacidsAntacids: Meals including onion have been used to induce heartburn, dyspepsia, gastric acidity, and gastroesophageal reflux in clinical trial (8; 9).
  • AntibioticsAntibiotics: In laboratory study, onion exhibited antibacterial effects on Gram-negative and Gram-positive bacteria, including Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella spp., Shigella dysenteriae, Streptococcus faecalis, Streptococcus mutans, Streptococcus sobrinus, Porphyromonas gingivalis, Prevotella intermedia, Salmonella typhimurium, and Escherichia coli (12; 23; 19; 313; 314; 22).
  • Anticoagulants and antiplateletsAnticoagulants and antiplatelets: In pharmacologic and in vitro study, onion and onion extract, alone and in combination with other products, have shown hemostatic effects, including inhibited platelet aggregation, reduced plasma viscosity, decreased hematocrit, and increased fibrinolytic activity (145; 146; 147; 148; 149; 150; 151; 152; 153; 121; 154; 155; 156; 68; 157; 158; 159; 160; 161; 162; 163; 164; 165; 166; 167; 168; 169; 315).
  • AntidepressantsAntidepressants: In a rat behavioral model, onion administration exerted antidepressant effects independent of the hypothalamic-pituitary-adrenal axis (84). In a forced-swimming test in rats, onion suppressed an increase in the turnover of dopamine (84).
  • AntidiabeticsAntidiabetics: Based on human, animal, and laboratory study, onion (Allium cepa) has been found to possess antidiabetic potential (172; 170; 173; 174; 175; 176; 177; 178; 179; 180; 181; 182; 183; 184; 185; 186; 187; 188). The hypoglycemic effects of onion may be dependent on the stimulation of insulin secretions (178).
  • AntifungalsAntifungals: In laboratory study, onion displayed antifungal activity against various fungi, including Candida spp, Malassezia furfur, Achorion schoenleinii, Trichophyton gypseum asteroides, and Microsporon gypseum (316; 30; 31).
  • AntihypertensivesAntihypertensives: Based on human and animal study, onion and quercetin may reduce blood pressure (190; 146; 191; 192).
  • Anti-inflammatoriesAnti-inflammatories: Flavonoids like those found in onion have been found to exert anti-inflammatory effects and inhibit cyclooxygenase-2 (COX-2) transcription (317).
  • AntilipemicsAntilipemics: In animal and human (203) study, onion has been found to exert hypolipemic effects and lower various lipid parameters including total cholesterol, triglycerides, phospholipids, and triacylglycerol, and to increase the HDL cholesterol/total cholesterol ratio (300; 318; 319; 320; 321; 204; 148; 322; 323; 66; 324). Not all studies have found onion to have favorable effects on lipids. In animal study, whole onion has been found to lower cholesterol, whereas onion extract and residue were found to elevate cholesterol (204; 205). Dietary onion reportedly increased plasma triglyceride levels in quail (206).
  • AntineoplasticsAntineoplastics: In vitro, animal, and epidemiological study indicates that onion or onion extract prevents cancer, including gastrointestinal cancer, ovarian cancer, and skin cancer (12; 325; 326; 327; 37; 328; 329; 172; 330; 331; 332). The most common current theory is that the metabolites of organosulfur compounds, specifically S-alk(en)yl cysteine sulfoxide, found in onion inhibit mutagenesis, induce phase II detoxification enzymes, influence cell arrest and apoptosis, scavenge free radicals, enhance focus formation by increasing cell proliferation, and inhibit DNA adduct formation (330; 172; 329; 325; 327; 37; 333; 334; 335; 128; 336; 337; 338; 339; 340).
  • Cytochrome P450: substrates, inhibitors, inducersCytochrome P450: substrates, inhibitors, inducers: In animal study, onion and quercetin were found to reduce the bioavailability of cyclosporine (201; 202). Quercetin has been found to inhibit cytochrome P450 2C8 (194; 195; 196), 2C9 (197; 198), 2D6 (197; 198), 2E1 (199), and 3A4 (197; 198). In rat study, onion consumption induced CYP1A and 2B activity (199). Organosulfur compounds have been found to inhibit CYP2A6 in humans (200).
  • Drugs used for osteoporosis Drugs used for osteoporosis: Perimenopausal and postmenopausal women who consumed onion daily were found to have increased bone density compared to those who consumed onion once a month or less (341). In animal study, ingestion of onion significantly reduced bone loss and inhibited bone resorption (342; 343; 104; 344; 345; 346).
  • EstrogensEstrogens: In human study, subjects that consumed a legume/Allium diet (containing garbanzo beans, garlic, and onions) were found to excrete more urinary isoflavonoid phytoestrogens and lignans (347).
  • Low-molecular-weight heparins (LMWHs)Low-molecular-weight heparins (LMWHs): Based on clinical trial, cepae extract from onions, heparin, and allantoin may improve healing of injuries incurred during laser tattoo removal or surgery (139; 140; 141; 142; 143; 144).
  • NicotineNicotine: In rat study, onion oil protected against the oxidative damage caused by nicotine (348; 349).
  • P-glycoprotein-regulated agentsP-glycoprotein-regulated agents: Based on clinical and animal study, quercetin may act as a modulator of p-glycoprotein and may alter the levels of agents transported by this pump (195; 198).
  • SimvastatinSimvastatin: Onion was found to restore the reduced Na efflux through Na-K ATPase and Na-K cotransport in simvastatin-treated hypercholesterolemic rats (148).
  • TriamcinoloneTriamcinolone: In human study, combined use of onion extract gel with triamcinolone acetonide was more effective in the treatment of keloids and scars than that of triamcinolone acetonide (212).
  • Uridine diphosphate glucuronosyl transferase (UGT) substratesUridine diphosphate glucuronosyl transferase (UGT) substrates: In rat and humans in vivo study, onion and quercetin were found to induce UGT activity (350; 199) and may alter the effects of drugs metabolized through this system.

    • Onion/Herb/Supplement Interactions:

  • AntibacterialsAntibacterials: In laboratory study, onion exhibited antibacterial effects on Gram-negative and Gram-positive bacteria, including Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella spp., Shigella dysenteriae, Streptococcus faecalis, Streptococcus mutans, Streptococcus sobrinus, Porphyromonas gingivalis, Prevotella intermedia, Salmonella typhimurium, and Escherichia coli (12; 23; 19; 313; 314; 22).
  • Anticoagulants and antiplateletsAnticoagulants and antiplatelets: In pharmacologic and in vitro study, onion and onion extract, alone and in combination with other products, have shown hemostatic effects, including inhibited platelet aggregation, reduced plasma viscosity, decreased hematocrit, and increased fibrinolytic activity (145; 146; 147; 148; 149; 150; 151; 152; 153; 121; 154; 155; 156; 68; 157; 158; 159; 160; 161; 162; 163; 164; 165; 166; 167; 168; 169; 315).
  • Antidepressant herbs and supplementsAntidepressant herbs and supplements: In a rat behavioral model, onion administration exerted antidepressant effects independent of the hypothalamic-pituitary-adrenal axis (84). In a forced-swimming test in rats, onion suppressed an increase in the turnover of dopamine (84).
  • AntifungalsAntifungals: In laboratory study, onion displayed antifungal activity against various fungi, including Candida spp, Malassezia furfur, Achorion schoenleinii, Trichophyton gypseumasteroides, and Microsporon gypseum (316; 30; 31).
  • Antihypertensive agentsAntihypertensive agents: Based on human and animal study, onion and quercetin may reduce blood pressure (190; 146; 191; 192).
  • Anti-inflammatory agentsAnti-inflammatory agents: Flavonoids like those found in onion have been found to exert anti-inflammatory effects and inhibit cyclooxygenase-2 (COX-2) transcription (317).
  • Antilipemic agentsAntilipemic agents: In animal and human (203) study, onion has been found to exert hypolipemic effects and lower various lipid parameters, including total cholesterol, triglycerides, phospholipids, and triacylglycerol, and to increase the HDL cholesterol/total cholesterol ratio (300; 318; 319; 320; 321; 204; 148; 322; 323; 66; 324). Not all studies have found onion to have favorable effects on lipids. In animal study, whole onion has been found to lower cholesterol, whereas onion extract and residue were found to elevate cholesterol (204; 205). Dietary onion reportedly increased plasma triglyceride levels in quail (206).
  • AntineoplasticsAntineoplastics: In vitro, animal, and epidemiological study indicates that onion or onion extract prevents cancer, including gastrointestinal cancer, ovarian cancer, and skin cancer (12; 325; 326; 327; 37; 328; 329; 172; 330; 331; 332). The most common current theory is that the metabolites of organosulfur compounds, specifically S-alk(en)yl cysteine sulfoxide, found in onions, inhibit mutagenesis, induce phase II detoxification enzymes, influence cell arrest and apoptosis, scavenge free radicals, enhance focus formation by increasing cell proliferation, and inhibit DNA adduct formation (330; 172; 329; 325; 327; 37; 333; 334; 335; 128; 336; 337; 338; 339; 340).
  • AntioxidantsAntioxidants: The antioxidant effects of onion are well documented and likely due to the flavonoid content (10; 176; 178; 47; 351; 48; 352; 353; 354; 355; 354; 356; 357; 358; 85; 359; 360; 53; 361; 362; 348; 363; 48; 364; 33; 52; 176; 365; 366). In laboratory and animal study, onion extract or its flavonoid constituents have been found to increase total antioxidant (351; 357), super oxide dismutase, glutathione peroxidase, and catalase levels (351). Rises in free radicals and other reactive oxygen species and lipid oxidation have been inhibited (47; 48; 352; 85; 359; 362).
  • Beta-caroteneBeta-carotene: Onion was found to minimize the loss and enhance the bioaccessibility of beta-carotene from cooked vegetables such as carrots (367).
  • Cytochrome P450: substrates, inhibitors, inducersCytochrome P450: substrates, inhibitors, inducers: In animal study, onion and quercetin were found to reduce the bioavailability of cyclosporine (201; 202). Quercetin has been found to inhibit cytochrome P450 2C8 (194; 195; 196), 2C9 (197; 198), 2D6 (197; 198), 2E1 (199), and 3A4 (197; 198). In rats, onion consumption induced CYP1A and 2B activity (199). Organosulfur compounds have been found to inhibit CYP2A6 in humans (200).
  • Fish oilFish oil: In animal study, the concurrent ingestion of fish oil with onion was found to enhance the bioavailability of quercetin glucosides (368).
  • Green teaGreen tea: In animal study, supplementation with quercetin and red onions increased the bioavailability of epigallocatechin gallate from green tea extract (369).
  • HypoglycemicsHypoglycemics: Based on human, animal, and laboratory study, onion (Allium cepa) has been found to possess antidiabetic potential (172; 170; 173; 174; 175; 176; 177; 178; 179; 180; 181; 182; 183; 184; 185; 186; 187; 188). The hypoglycemic effects of onion may be dependent on the stimulation of insulin secretions (178).
  • LecithinLecithin: In animal study, the concurrent ingestion of lecithin with onion was found to enhance the bioavailability of quercetin glucosides (368).
  • Osteoporosis herbs/supplementsOsteoporosis herbs/supplements: Perimenopausal and postmenopausal women who consumed onion daily were found to have increased bone density compared to those who consumed onion once a month or less (341). In animal study, ingestion of onion significantly reduced bone loss and inhibited bone resorption (342; 343; 104; 344; 345; 346).
  • P-glycoprotein-regulated agentsP-glycoprotein-regulated agents: Based on clinical and animal study, quercetin may act as a modulator of p-glycoprotein and may alter the levels of agents transported by this pump (195; 198).
  • PhytoestrogensPhytoestrogens: In human study, subjects that consumed a legume/Allium diet (containing garbanzo beans, garlic, and onions) were found to excrete more urinary isoflavonoid phytoestrogens and lignans (347).
  • SeleniumSelenium: In comparative study, allium vegetables like onion were identified as sources of selenium (370).
  • Soybean oilSoybean oil: In animal study, the concurrent ingestion of soybean oil with onion was found to enhance the bioavailability of quercetin glucosides (368).
  • Uridine diphosphate glucuronosyl transferase (UGT) substratesUridine diphosphate glucuronosyl transferase (UGT) substrates: In rats and humans in vivo, onion and quercetin were found to induce UGT activity (350; 199) and may alter the effects of drugs metabolized through this system.

    • Onion/Food Interactions:

  • Beta-carotene-containing vegetablesBeta-carotene-containing vegetables: Onion was found to minimize the loss and enhance the bioaccessibility of beta-carotene from cooked vegetables such as carrots (367).
  • ButterButter: Concurrent use of butter and onion may alter coagulability of blood in humans (371).
  • EmulsifiersEmulsifiers: In animal study, the concurrent ingestion of emulsifiers (sodium caseinate, sucrose fatty acid ester) with onion were found to enhance the bioavailability of quercetin glucosides (368)
  • Fats and lipidsFats and lipids: In animal study, a high-fat diet was found to impair the antidiabetic effects of onion (372). In animal study, the concurrent ingestion of lipids (soybean oil, fish oil, beef tallow, lecithin) with onion were found to enhance the bioavailability of quercetin glucosides (368).
  • LactaseLactase: Based on in vitro study in human epithelial colorectal adenocarcinoma Caco-2 cells, lactase may increase the bioavailability of quercetin (373).
  • PotatoPotato: Heated onion extract may have an inhibitory effect on the browning of potatoes; this effect was dependent on temperature and may be increased by the addition of glycine and glucose (374).

    • Onion/Lab Interactions:

  • Blood pressureBlood pressure: Based on human and animal study, onion and quercetin may reduce blood pressure (190; 146; 191; 192).
  • Bone density scansBone density scans: Perimenopausal and postmenopausal women who consumed onion daily were found to have increased bone density compared to those who consumed onion once a month or less (341). In animal study, ingestion of onion significantly reduced bone loss and inhibited bone resorption (342; 343; 104; 344; 345; 346).
  • Coagulation panelCoagulation panel: Based on pharmacologic and in vitro study, onion and onion extract may inhibit platelet aggregation, reduce plasma viscosity, decrease hematocrit, and increase fibrinolytic activity (145; 146; 147; 300; 375). However, two in vivo clinical studies indicated that raw onions do not significantly affect platelet aggregation, thromboxane B2 production, factor VII, or other hemostatic variables (301; 302).
  • Complete blood count (CBC)Complete blood count (CBC): In animal study, onion consumption reduced hemoglobin, red blood cells (erythrocytes), and segmented neutrophils in a dose-dependent manner (323; 376); other cell counts were unaffected (323). Erythrocytes were found retain normal appearance in animals fed a cholesterol-enriched diet along with onion extract, whereas the cholesterol-enriched diet alone caused the erythrocytes to change shape and aggregate (377).
  • Glucose levelsGlucose levels: Based on human, animal, and laboratory study, onion has been found to possess antidiabetic potential and may reduce blood glucose levels (172; 170; 173; 174; 175; 176; 177; 178; 179; 180; 181; 182; 183; 184; 185; 186; 187; 188). The hypoglycemic effects of onion may be dependent on the stimulation of insulin secretions (178).
  • Hormone panelHormone panel: In animal study, fresh onion juice was found to increase serum total testosterone and luteinizing hormone (LH) levels; follicle-stimulating hormone (FSH) levels were not significantly affected (115).
  • Lipid profileLipid profile: In animal and human (203) study, onion has been found to exert hypolipemic effects and lower various lipid parameters including total cholesterol, triglycerides, phospholipids, and triacylglycerol and to increase the HDL cholesterol/total cholesterol ratio (300; 318; 319; 320; 321; 204; 148; 322; 323; 66; 324). Not all studies have found onion to have favorable effects on lipids. In animal study, whole onion has been found to lower cholesterol, whereas onion extract and residue were found to elevate cholesterol (204; 205). Dietary onion reportedly increased plasma triglyceride levels in quail (206).
  • Liver function testsLiver function tests: Onion juice reduced aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), and alkaline and acid phosphatases (AlP, AcP) activities in alloxan-diabetic rats (174).
  • Uric acidUric acid: Oral administration of onion reduced serum uric acid levels in hyperuricemic rats (312).