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The question

I recently decided to clean out my medicine cabinet of old and unused prescription drugs. I did a Google search to find out what do with them. The website of the U.S. Food and Drug Administration says it's okay to flush some drugs, like opioids, down the toilet. But Health Canada's website says you should never flush away any drugs because it's bad for the environment. Who is right?

The answer

The first thing you need to know is that there are places to safely dispose of your medications without dumping them down a drain where they can end up in rivers and lakes and potentially harm aquatic life.

Most pharmacies, in Canada and the United States, will take back drugs, which are then sent to special facilities for disposal. In many cases, the drugs are incinerated –eliminating any chance they will end up in the wrong place.

Unfortunately, most people don't take advantage of the return programs – at least not in a prompt fashion.

"A lot of medicine cabinets are chock-a-block full of stuff like opioids," says Dr. Donald Redelmeier, a staff physician at Sunnybrook Health Sciences Centre in Toronto.

Indeed, he notes, some physicians overprescribe opioids, especially to patients having operations.

"Surgery hurts, so it's perfectly logical to prescribe painkillers," Redelmeier says. "And because doctors don't want patients to run short, there's a tendency to send people home from the hospital with far too much narcotics."

One study found only 41 per cent of the dispensed tablets are actually used for postsurgery pain.

Redelmeier says people sometimes inappropriately use their opioid stash when they have a minor pain long after their operations – potentially starting them down the road to drug dependency. Other family members, or visitors, may steal the drugs for "recreational" purposes, he adds.

To reduce the risk of drug misuse and abuse, the U.S. FDA says it's important to get rid of certain drugs – especially opioids such as fentanyl and oxycodone – as soon as they're no longer medically needed. Although medicine take-back programs are still the FDA's preferred disposal method, the U.S. government agency says opioids can also be put down a drain.

"We believe the known risks of harm and even death to humans from accidental exposure to certain potent opioids … far outweighs any potential risk to humans or the environment from flushing," FDA spokesperson Sarah Peddicord says.

In Canada, however, authorities have adopted a different approach. They put the emphasis on the medication-return programs and advise against dumping any drugs down drains.

The Canadian recommendations arise from growing concerns about the effects of pharmaceutical products on aquatic life. Medications literally pass through patients, ending up in their urine and feces. Many waste-treatment plants can't remove the drugs before the water is released back into the environment, Health Canada spokesperson Anna Maddison said in an e-mail. Deliberately dumping drugs down the drain only makes this problem worse.

Overall, the concentration of pharmaceuticals in surface water is extremely diluted. Even so, "chronic low levels of exposure can have negative impacts," Maddison says.

For instance, studies show that birth-control hormones in rivers and lakes can disrupt fish reproduction, leading to "intersex" offspring with both male and female characteristics.

Other research suggests antidepressants in waterways can alter fish behaviour, making them less likely to swim together in schools and thereby lowering their chances of survival.

Not much is known about the possible impact of opioids on wildlife, says Chris Metcalfe, a professor in the School of the Environment at Trent University in Peterborough. The fact is that little research has been done in this area, he says.

About 10 per cent to 20 per cent of the pharmaceutical products passing through sewage-treatment plants come from drugs dumped directly down drains. The other 80 per cent to 90 per cent is in excreted human waste.

Metcalfe applauds Health Canada's efforts to discourage drain disposal. "Whatever we can do to reduce the discharge of pharmaceuticals into the sewage system is a good thing."

Not everyone in Canada agrees. "A strong case can be made to flush drugs. It's fast, easy and irreversible," says Dr. David Juurlink, a drug-safety expert and head of clinical pharmacology and toxicology at Sunnybrook.

A recent study, co-authored by Juurlink, revealed that young children are much more likely to suffer an accidental overdose when opioids have been prescribed to their mothers. "For some opioids, a single tablet is enough to kill a child," Juurlink warns.

Of course, to flush or not to flush wouldn't be an issue if people returned their leftover drugs to pharmacies right away. But maybe that's too much to expect from human nature. After all, many of us are procrastinators. And it's awfully hard to let go of something that's still perfectly usable.

Paul Taylor is a Patient Navigation Adviser at Sunnybrook Health Sciences Centre. He is a former health editor of The Globe and Mail. You can find him on Twitter @epaultaylor and online at Sunnybrook's Your Health Matters.