Goldenseal:

Goldenseal has been shown to speed up recovery time in subjects with diarrhea, and decrease diarrhea volume in clinical studies (43). In one study, 400mg of goldenseal (berberine sulfate) produced a significantly higher rate of recovery from E. coli-induced diarrhea within 24 hours of treatment and significantly lower stool volume in subjects with cholera-induced diarrhea. Other research has also indicated that goldenseal may be beneficial for some forms of diarrhea (44,45).

It has been reported that Goldenseal is well tolerated at the therapeutic dose of 500mg (55).  

Although goldenseal is generally nontoxic at recommended dosages, at high dosages goldenseal may interfere with vitamin B metabolism (63).  It has been stated that people with high blood pressure should avoid goldenseal (63). If you are pregnant or nursing, or taking a prescription medication, consult a physician before using this product.

(43) - Khin MU, Myo K, Nyunt NW, Aye K, Tin U. Clinical trial of berberine in acute watery diarrhea. Br Med J (Clin Res Ed) 1985;291:1601-5.

(44) - Sack RB, Froelich J. Berberine inhibits intestinal secretory response of Vibrio cholerae and Escherichia coli enterotoxins. Infection and Immunity 1982;471-5.

(45) - Kamat SA. Clinical trials with berberine hydrochloride for the control of diarrhea in acute gastroenteritis. J Assoc Physicians India 1967;15:525-9.

(55) - Snow JM. Hydrastic candensis L .(Ranunculaceae). 1996.

(63) - Anonymous. Hydrastis canadensis L. (Ranunculaceae)—Goldenseal. In: CRC Handbook of Medicinal Herbs, edited by JA Duke.  Boca Raton, FL:CRC Press, Inc., 1985, pp. 238-239. 

http://www.vitacost.com/science/hn/Concern/Diarrhea.htm

Due to of its supposed antimicrobial activity, goldenseal has a long history of use for infectious diarrhea. Its major alkaloid, berberine (also found in barberry and Oregon grape), has been shown to improve infectious diarrhea in some double-blind trials.51 Negative studies have generally focused on people with cholera, while positive studies investigated viral diarrhea or diarrhea due to strains of E. coli. These studies generally used 400–500 mg berberine one to three times per day. Because of the low amount of berberine in most goldenseal products, it is unclear how effective the whole root or root extracts would be in treating diarrhea.

http://www.ajc.com/health/altmed/shared/health/alt_medicine/ConsHerbs/Goldensealch.html

Today, goldenseal is marketed as a tonic to aid digestion and sooth upset stomach. It is also considered a natural antibiotic and is often combined with echinacea in preparations designed to strengthen the immune system. Many professional herbalists recommend goldenseal in herbal remedies for hay fever (also called allergic rhinitis), colds, and flu. Goldenseal is considered a useful antiseptic (which is why some herbalists use it topically to disinfect cuts and scrapes) and astringent, and is commonly used to treat a host of skin, eye, and mucous membrane inflammatory and infectious conditions (such as sinusitis, conjunctivitis ["pink eye"], and urinary tract infections). It is also available in mouthwashes for sore throats and canker sores.

Laboratory studies suggest that this substance has antibacterial and immune-enhancing properties and may also have cardiovascular benefits.

http://www.healthy.net/scr/article.asp?ID=1906

Its bitter stimulation helps in loss of appetite, and the alkaloids it contains stimulate bile production and secretion. All catarrhal conditions improve with Golden Seal, especially sinus ones. The anti-microbial properties appear to due to alkaloids present. As an example of research that has been done on plant constituents we shall consider berberine. Berberine, found in a number of other herbs as well, has antibiotic, immuno-stimulatory, antispasmodic, sedative, hypotensive, uterotonic, cholerectic, & carminative activity. Its demonstrable pharmacological activities strongly contribute to the therapeutic use of Hydrastis. Berberine has marked antimicrobial activity, and whilst not in the same league as antibiotics, ithas a broad spectrum of antimicrobial activity. In vitro antimicrobial effects have been demonstrated against bacteria, protozoa, and fungi, including:

Staphyloccus spp.
Streptoccus spp.
Chlamydia spp.
Corynebacterium diphtheria
Escherichia coli
Salmonella typhi
Vibrio cholerae
Diplococcus pneumonia
Pseudomonas spp.
Shigella dysenteriae
Entamoeba histolytica
Trichomonas vaginalis
Neisseria gonorrhoeae
Neisseria meningitidis
Treponema pallidum
Giardia lamblia
Leishmania donovani
Candida albicans.

Berberine's action against some of these pathogens is actually stronger than that of antibiotics commonly used, however, please remember that we are dealing with whole plants and not extracted constituents. Berberine'saction in inhibiting Candida, as well as other pathogenic bacteria, prevents the overgrowth of yeast that is a common side effect of antibiotic use. This fascinating alkaloid increases blood supply to the spleen. This improved blood supply may promote optimal activity of the spleen by increasing the release of compounds that potentiate immune response. It has also been shown to activate macrophages in a number of ways. Coupled with its ability to inhibit tumor formation in the laboratory, suggests that berberine possesses some antineoplastic activity.

Berberine has been shown in several clinical studies to stimulate the secretion of bile (i.e. it is a cholerectic) and bilirubin. One clinical trial that examined the effect of berberine on 225 patients with chronic cholecystitis. Oral doses of 5 to 20 mg three times a day before meals caused, over a period of 24-48 hours, disappearance of clinical symptoms, decrease inbilirubin level, and an increase in the bile volume of the gallbladder. Berberine corrects the elevated levels of tyramine found in patients with liver cirrhosis. It prevents the elevation of serum tyramine following oral tyrosineload, by inhibiting the enzyme tyrosine decarboxylase found in bacteria in the large intestine.

Traditionally Hydrastis canadensis has been used during labour to help contractions, but it is for just this reason that it should be avoided during pregnancy. Applied externally it can be helpful in eczema, ringworm, itching, earache and conjunctivitis.

Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications; 1998:78.

Duke JA. Handbook of Phytochemical Constituents of GRAS Herbs and Other Economic Plants. Boca Raton, Fla: CRC Press; 1992.

Foster S, Tyler VE. Tyler's Honest Herbal. 4th ed. New York: The Haworth Herbal Press; 1999:195-197.

Karch SB. The Consumer's Guide to Herbal Medicine. Hauppauge, New York: Advanced Research Press; 1999:102-103.

Khin-Muang-U, Myo-Khin, Nyunt-Nyunt-Wai, et al. Clinical trial of berberine in acute watery diarrhea. Br Med J 1985; 291:1601-5.

Lau CW, Yao XQ, Chen ZY, Ko WH, Huang Y. Cardiovascular actions of berberine. [review]. Cardiovasc Drug Rev. 2001;19(3):234-244.

Periera da Silva A, Rocha R, Silva CM, Mira L, Duarte MF, Florencio MH. Antioxidants in medicinal plant extracts. A research study of the antioxidant capacity of Crataegus, Hamamelis and Hydrastis. Phytother Res. 2000;14(8):612-616.

Rabbani GH, Butler T, Knight J, et al. Randomized controlled trial of berberine sulfate therapy for diarrhea due to enterotoxigenic Escherichia coli and Vibrio cholerae. J Infect Dis 1987; 155:979-84.

Rotblatt M, Ziment I. Evidence-Based Herbal Medicine. Philadelphia, PA: Hanley & Belfus, Inc; 2002:221-225.

Scazzocchio F, Cometa MF, Tomassini L, Palmery M. Antibacterial activity of Hydrastis canadensis extract and its major isolated alkaloids. Planta Med. 2001;67(6):561-564.

Swanston-Flatt SK, et al. Evaluation of traditional plant treatments for diabetes: studies in streptozotocin diabetic mice. Acta Diabetol Lat. 1989;26:51–55.

White L, Mavor S. Kids, Herbs, Health. Loveland, Colo: Interweave Press; 1998:22, 32.