The warning comes six years after the FDA warned parents against using Hyland's Teething Tablets. Regulators said a laboratory analysis found that the tablets used an inconsistent amount of belladonna, a substance that can be toxic in large doses.

Belladonna, also known as deadly nightshade, is not uncommon in homeopathic remedies and is used by Hyland's to combat redness, inflammation and general discomfort.

In a statement, Hyland's described the FDA warning as a "surprise" and said the company is "confident that Hyland's Baby Teething Tablets remain safe."

The company is cooperating with the FDA investigation, although it said it had yet to learn of any of the data supporting the FDA's warning.

The company's teething tablets are sold over the counter and are tested for excessive belladonna content and contaminants, Hyland's said.

"A 10-pound child would have to accidentally ingest, all at the same time, more than a dozen bottles of 135 Baby Teething Tablets before experiencing even dry mouth from the product," the company said in a statement.

"Additionally, the body clears belladonna alkaloids from any single dose in a matter of hours," making it unlikely that the substance would build in a person's system, the company said.

The company also worried about "rumors" that cause "fear and worry" about belladonna.

"This new FDA statement increases the confusion," the company said. "The safety and effectiveness of Hyland's natural homeopathic medicines is our top priority. That's why we work with regulators to ensure that our products meet the highest standards."

However, the FDA said the tablets and gels have not been evaluated or approved for either safety or efficacy by the government agency. Regulators said they were unaware "of any proven health benefit of the products."

The FDA is investigating the issue. Among other steps, regulators are testing product samples to determine whether there are unsafe levels of belladonna or other substances.