Less-than-clear packaging could lead many parents to mistakenly believe over-the-counter cold medicines are safe for infants and toddlers, researchers reported Tuesday.

Last year, the U.S. Food and Drug Administration (FDA) issued an advisory recommending that parents not give over-the-counter cold and cough medicines to children younger than 2.

The medications, which have never been proven effective in children, have been implicated in the deaths of more than 100 infants in the U.S. in the past 40 years. They have also been linked to seizures, hallucinations and other serious side effects in children.

Manufacturers have stopped marketing cold medicines aimed at the youngest children, but products for children ages 4 and older remain on the market.

The new study, published in the journal Pediatrics, suggests that if labels are not clear enough in their warnings, many parents may mistakenly think the cold drugs are safe for infants and toddlers.

Researchers had 182 parents of infants, mostly mothers, read the packaging on four different cold and cough medications that have since been pulled from the market. The products were aimed at infants and children, but the dosing instructions advised parents to consult a doctor before giving the drug to a child younger than 2.

The parents had an average of 12.5 years of education and 99 percent had adequate literacy skills. However, only 17 percent had numeracy skills above the 9th grade level.

The researchers found that nearly three quarters of parents who read each product's packaging in full said they would give at least one of the four medications to a 13-month-old with cold symptoms.

Parents were commonly influenced by packaging features other than the dosing instructions, such as graphics of teddy bears or wording such as "pediatrician recommended."

The findings have implications for over-the-counter cold drugs still on the market, according to Dr. Russell L. Rothman, the senior researcher on the study.

"We believe that manufactures and the FDA should work together to improve current over-the-counter labels," said Rothman, of Vanceril University Medical Center in Nashville, Tennessee.

"This includes removing misleading graphics, using more uniform, plain language, improving the display of quantitative information, and simplifying the Drug Facts Panel component of the label," he told Reuters Health.

The "Drug Facts" portion of medication labels contains the dosing instructions and safety warnings, and its complexity may make it hard for parents to "navigate," Rothman and his colleagues write.

Rothman pointed out that questions remain about the use of cold medicines in older children as well. An expert advisory panel to the FDA recommended that the drugs be banned for children younger than 6 years old — an issue the agency is still studying — and many manufacturers suggest that parents not give them to children younger than 4 years old.

"Any parent considering using these medicines in younger children should read the labels carefully, and discuss what to do with their physician, pharmacist or other healthcare provider," Rothman said.