Thanks for bringing up this topic! I've gone around several posts explaining why GSE is bad, from what I've learned, but it's still widely used.
That article is a good start! There is also an interview with Richard Perry, Citricidal's manager:
Here's some stuff from Wikipedia that may be helpful:
Nevertheless, as a result of marketing by manufacturers in the health food arena and a few misinterpreted studies conducted in vitro that tested contaminated extracts which were not pure GSE processed without solvents or brands which are known to contain preservatives, the controversy over the effectiveness of GSE continues even when studies conclude – self-made pure GSE has no natural antimicrobial properties and commercial GSE has been identified with contamination from synthetic preservatives.
Independent studies have shown that commercial preparations contain the compound benzalkonium chloride, which is a synthetic antimicrobial commonly used in disinfectants and cleaning products, the related compound benzethonium chloride, the antibiotic triclosan, or the preservative methylparaben. Some samples were shown to contain up to 22% benzalkonium chloride by weight, despite the known allergenicity and toxicity of the compound at higher doses. These chemicals were not present in grapefruit seed extracts prepared in the laboratory, and GSE preparations without the contaminants were found to possess no significant antimicrobial effect.
Here's some info from a Naturopathic Clinic (also at the bottom of the Wikipedia page):
The Grapefruit Seed Extracts that were found to have significant antimicrobial properties were also found to contain preservatives. Does that make sense? Now why would an antimicrobial extract, presumably powerful, in its full strengh, need a preservative?
Now there are GSE's out there which now boast of containing NO added synthetic preservatives, but these were found ineffective against microbes and fungi in lab tests.
Either way, it is not a "natural," substance, but one derived through a synthetic "secret," process that the companies will not divulge.
There is some evidence that the actual, natural, extract of the grapefruit seed (pulp and its juice) does contain some beneficial properties, but these are very small and there are other ways to get larger quantities of these without risking Rx overdose.
It is very dangerous for those taking Rx's to take any grapefruit containing product since it can increase the potency of many drugs. I'm not saying stop eating grapefruits, but be cautious when taking Rx, especially of these so-called "extracts!"
Grapefruit can have a number of interactions with drugs, often increasing the effective potency of compounds. Grapefruit contains naringin, bergamottin and dihydroxybergamottin, which inhibit the protein isoform CYP3A4 predominately in the liver. It is via inhibition of this enzyme that grapefruit increases the effects of a variety of drugs. The effect of grapefruit juice with regard to drug absorption was originally discovered in 1989. However, the effect became well-publicized after being responsible for a number of deaths due to overdosing on medication.
Grapefruit juice may be the first documented, but apple and orange juices have been also implicated in interfering with etoposide, a chemotherapy drug, some beta blocker drugs used to treat high blood pressure, and cyclosporine, taken by transplant patients to prevent rejection of their new organs.