Gingko: Can inhibit clotting - should not be used with aspirin or other nonsteroidal anti-inflammatory drugs or with anticoagulants such as warfarin or heparin, or in conjunction with anticonvulsant drugs used by epileptics, such as carbamazepine, phenytoin or phenobarbital, or with tricyclic antidepressants.

Ginseng: Should not be used with warfarin, heparin, aspirin and other nonsteroidal anti-inflammatory drugs because it can inhibit clotting. Also may cause headache, tremulousness and manic episodes in patients treated with phenelzine sulfate. Should not be used with estrogens or corticosteroids because it may add to those drugs' side effects. May also interfere with the heart drug digoxin or with digoxin monitoring. Should not be used by diabetics because it can affect blood glucose levels.

Karela: Should not be used by patients with diabetes because it can affect blood glucose levels.

Kava: Should not be used with the tranquilizer alprazolam because it may result in coma.

Kelp: May interfere with thyroid therapies.

Mugwort: Do not use if pregnant or nursing.

Licorice: Can offset the effect of the diuretic drug spironolactone. May also interfere with heart drug digoxin or with digoxin monitoring.

St. John's Wort: Can produce skin reactions to light if you're fair-skinned -take care! Anyone taking other drugs that cause light sensitivity, such as piroxicam or tetracycline, may want to avoid this herb. The active ingredient in St. John's Wort is uncertain, so it should not be used with two common types of psychiatric drugs called monoamine oxidase inhibitors and selective serotonin reuptake inhibitors. Tannic acid in the herb may inhibit absorption of iron.

Valerian: Should not be used with barbiturates, such as thiopental and pentobarbital.