The idea of homeopathy is to dilute an active ingredient down, usually with water, until there are only trace amounts left. Advocates claim that a tiny trace amount of a substance that causes symptoms of a disease in healthy people would cure similar symptoms in sick people.

Normally homeopathists dilute the active ingredient down to such a minuscule amount that there is just the tiniest amount of the ingredient left, which won't do anything good for you, other than perhaps a mild placebo effect, but at least you can be pretty confident that you aren't being poisoned. You're basically eating very expensive sugar, or drinking slightly funny-tasting water.

However, when the US Food and Drugs Administration (FDA) carried out an inspection of products from Canadian-based homeopathy company Homeolab USA, it found variable amounts of belladonna in its products.

Specifically, it found the ingredient more commonly known as deadly nightshade in products designed to be given to teething babies.

The FDA sent a stern letter to Homeolab USA about the levels of nightshade found within their products, which it published on its website on Wednesday. It doesn't mince words.

"Your operators use an inherently variable process, to produce in-process powder blends, including those made from toxic ingredients. You did not test the in-process powder blends for adequacy of mixing to assure uniformity and homogeneity prior to release and shipment to your contract manufacturer, Raritan," the letter reads.

"Your Infants’ Teething Tablet contains belladonna. Raritan uses this powder blend mixture to produce finished drug products for infants and children, a population vulnerable to the toxic effects of belladonna...

"You shipped [..] Infants’ Teething Tablets to the U.S. market before evaluating whether your manufacturing process was reliable and reproducible."

Atropa belladonna is a plant that was used to make poison arrows by early humans. Side effects of taking belladonna can include blurred vision, red dry skin, fever, fast heartbeat, inability to urinate or sweat, hallucinations, spasms, mental problems, convulsions, and coma, according to the US National Library of Medicine.

Last year, the FDA warned against anyone using homeopathic teething tablets or gels, after several cases of babies suffering seizures with symptoms akin to deadly nightshade poisoning were reported to them.

"Consumers should seek medical care immediately if their child experiences seizures, difficulty breathing, lethargy, excessive sleepiness, muscle weakness, skin flushing, constipation, difficulty urinating, or agitation after using homeopathic teething tablets or gels," the FDA states on its website.

It advises anyone who has bought such products to dispose of them immediately.