The Food and Drug Administration warned Thursday that children and adolescents should not be prescribed cough and cold medicines containing codeine and hydrocodone because of serious safety risks posed by the opioid ingredients.

The agency said it is requiring manufacturers to change the wording on their labels to make clear that such products should not be used for anyone younger than 18. Common side effects of opioids include headache, dizziness and vomiting. Greater dangers include breathing difficulties and even death.

The FDA also said it is requiring manufacturers to add new safety warnings for adult use _ including an expanded boxed warning, the most prominent kind _ spelling out the risks of using medications with codeine and hydrocodone.

The new warnings are consistent with the labels on other drug products with opioids, including painkillers.

Katie McPeak, medical director for primary care with St. Christopher's Hospital for Children, called Thursday's announcement a positive step because it will raise even more awareness about the opioid epidemic. However, she said the dangers to children from opioids have been long known _ not only the threat of addiction and breathing risks, but unpredictability of how individual children will metabolize the drugs.

McPeak, who graduated from medical school in 2001, said that in her career opioids have not been commonly given children in primary care. The exceptions are children with some chronic illnesses or cancer.

"There's no reason for any primary care doctor to prescribe opioids" to children, she said.

In April, the FDA announced that it was strengthening labeling on codeine and tramadol, both opioid pain relievers, to protect young children and nursing babies from breathing problems arising from the medications' use. Tramadol already didn't have FDA approval for children.

In the spring announcement, the FDA said both medications should not be given to children younger than 12 years old, children younger than 18 after surgery to remove tonsils or adenoids, or children ages 12 to 18 who are obese or have other conditions that can affect breathing. The federal directive also said mothers who are breast-feeding should not take the medications because the opioids could get passed on to their babies while nursing.

The new warning follows an extensive FDA review of data and a meeting of the agency's Pediatric Advisory Committee in September. The panel declared that the risks of using certain opioids in children's cough medications outweigh the benefits.

According to the agency, outside experts said that while some children's coughs require treatment, many get better on their own _ including ones that are the result of respiratory infections.

FDA Commissioner Scott Gottlieb, who has made battling the opioid epidemic a top priority, said in a statement Thursday that it is critical "to protect children from unnecessary exposure" to prescription cough medicines containing codeine or hydrocodone. "At the same time we're taking steps to help reassure parents that treating the common cough and cold is possible without using opioid-containing products," he said.

The agency urged parents to read the labels on prescription bottles. "If the medicine prescribed for your child contains an opioid, talk to your child's health care professional about a different, non-opioid medicine," it said.

Staff writer Rita Giordano contributed to this article.