Got some leftover drugs - the kind that someone else might want to use, such as painkillers or stimulants? Wrap them up in used kitty litter or other pet droppings, the US Government advises.

A pilot program at the Substance Abuse and Mental Health Services Administration (SAMHSA) is looking at ways people can safely dispose of unused prescription drugs that are liable to be abused.

The Food and Drug Administration recommends flushing some of the most dangerous ones down the toilet, including the strong, addictive painkillers oxycodone and fentanyl and stimulants such as methylphenidate.

But environmentalists worry about the effects on fish and amphibians.

On its website SAMHSA recommends ways to disguise leftover pills.

"Mixing prescription drugs with an undesirable substance, such as used coffee grounds or kitty litter, and putting them in impermeable, nondescript containers, such as empty cans or sealable bags, will further ensure the drugs are not diverted," it says.