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PICK up a glass, fill it from the tap and take a sip. You have just had a tiny dose of the pill your neighbour took days before.

Excreted and flushed through our sewage works and waterways, drug molecules are all around us. A recent analysis of streams in the US detected an entire pharmacy: diabetic meds, muscle relaxants, opioids, antibiotics, antidepressants and more. Drugs have even been found in crops irrigated by treated waste water.

The amounts that end up in your glass are minuscule, and won鈥檛 lay you low tomorrow. However, someone prescribed multiple drugs is more likely to experience side effects, and risks rise exponentially with each drug taken by a person over 65. So could tiny doses of dozens of drugs have an impact on your health?

鈥淲e don鈥檛 know what it means if you have a lifelong uptake of drugs at very low concentrations,鈥� says at the University of L眉neburg, Germany.

鈥淭hese drugs have been individually approved, but we haven鈥檛 studied what it means when they鈥檙e together in the same soup,鈥� says Mae Wu at the , a US advocacy group.

Learn from history

Thirty years ago, no one paid attention to endocrine disruptors, artificial chemicals found in a variety of materials. These environmental contaminants are now linked to breast cancer and abnormal development in children. The cocktail in our water involves many more compounds, so this time we can鈥檛 afford to wait for negative effects to emerge.

The issue of drugs in our water came to a head earlier this year when researchers were taken aback by the discovery of some drug residues in crops irrigated with treated waste water in Israel (Environmental Science & Technology, ).

To see if these residues passed into the body, at the Hebrew University of Jerusalem and his colleagues focused on an epilepsy drug called carbamazepine, which they detected in cucumbers, lettuce and other produce. Volunteers who consumed an irrigated crop had a dramatic spike in the drug鈥檚 levels in their urine, which took over a week to clear. Those who ate crops irrigated by fresh water saw no effect. 鈥淭his was a big surprise,鈥� says Chefetz, who plans to study at-risk groups such as pregnant women and children.

We shouldn鈥檛 worry about an instant effect in healthy adults, says Chefetz, as the levels were 10,000 times lower than from a 400 milligram pill. 鈥淏ut we don鈥檛 know what will happen with small children exposed to low levels of pharmaceuticals for a generation,鈥� he says, and it鈥檚 not practical or ethical to run a clinical trial. 鈥淭here鈥檚 no data about that.鈥�

Half of all irrigation water in Israel comes from recycled waste water, a process more countries are looking to use as water scarcities become more widespread. California plans to increase its use for crops in response to drought, for example. This suggests drug residues in our drinking water are set to rise. But fresh water isn鈥檛 immune either.

of the US Geological Survey and his team checked streams in the eastern US for 108 chemicals, a drop in the bucket of the 3000 drug compounds in use. One river alone had 45. And even though two-thirds of the streams weren鈥檛 fed by treated waste water, 95 per cent of them had the anti-diabetic drug metformin, probably from street run-off or leaky sewage pipes (Environmental Science & Technology, ).

鈥淭he number of chemicals we are exposed to is very, very large, and we don鈥檛 understand those impacts,鈥� says Bradley.

That鈥檚 perhaps unsurprising, given the level of drug use in the US (see 鈥�We know what you took last summer鈥�). Recent stats show one in five Americans had used three or more prescription drugs in the past 30 days.

Unknown cocktail

The big unknown is how these low-dose drug cocktails affect people. Usually, researchers assess risk by varying doses of one drug. They ask what dose causes a specific result, like mortality in a lab animal or signs of cancer. But you cannot assess multiple drugs in small doses over a long time period, says K眉mmerer.

鈥淚ndustry says we need sound science, but what does that mean?鈥� he says. 鈥淚f it鈥檚 a clear dose-effect relation, then we cannot establish this.鈥�

鈥淲e鈥檝e got hundreds of chemicals circulating in our blood that our grandparents did not have,鈥� says at Brunel University London. 鈥淲e can test each of these chemicals in turn and not see any adverse effect, but I鈥檓 not sure the whole mixture doesn鈥檛 do anything.鈥�

Some say the industry could do more. 鈥淥nce drugs are on the market, they claim they have no responsibility,鈥� says Chefetz. Bodies like the disagree. A spokesperson points to efforts like a collaboration within the to generate reliable ways of judging potential risk for pharmaceuticals.

Maybe we should accept we don鈥檛 know what is going on and take action to minimise the risks: a precautionary approach. There are two possible solutions.

One is to upgrade water treatment facilities. It鈥檚 an option Switzerland has gone for, but it isn鈥檛 cheap 鈥� it will cost the country over $1 billion. In England, it is estimated that just removing the hormone estradiol from sewage plants would cost billions of pounds.

鈥淭he public needs to decide if reducing these compounds is important enough to pay for,鈥� says Bradley.

鈥淲e don鈥檛 know what it means if you have a lifelong uptake of drugs at very low concentrations鈥�

Another issue is that treatment doesn鈥檛 remove all unwanted compounds and can transform some into new and unknown chemicals, says K眉mmerer. He argued against the approach last week at the conference in Paris.

Instead, he is calling for greener pharmaceuticals that degrade readily in the environment.

Traditionally, pharma firms have focused on the stability of drugs, ensuring their products have a long shelf life. K眉mmerer believes it鈥檚 time for a rethink. Existing drugs can be made to react and break down under conditions not found in the body, such as light or a specific pH. He has shown it鈥檚 possible to redesign drugs for heart disease so that they degrade faster in the environment (RSC Advances, ), though these molecules require testing before clinical use.

But if the companies won鈥檛 play ball, perhaps we need to hit them where it hurts 鈥� the bottom line. Drugs are assessed for their environmental impact but results cannot prevent them being sold. Doing so could shift thinking, but it is a big stick. Would blocking a cancer drug on environmental grounds really be acceptable?

Still, a ban could encourage firms to produce greener drugs. 鈥淭his could create revenue for innovative companies,鈥� says K眉mmerer. It鈥檚 thought some are already active in this area, but keeping the research under their hats, says of the Warner Babcock Institute for Green Chemistry in Wilmington, Massachusetts.

鈥淒rugs in the environment is a serious issue, but current regulations work against solving the problem by looking for stable drugs,鈥� he says. 鈥淭he fact you don鈥檛 hear about all these great things pharma is doing in this space doesn鈥檛 mean they are not doing it.鈥�

However we decide to deal with the drugs in our water, the lessons of the endocrine disruptors suggest we should start soon, even in the face of uncertainty about their effects.

鈥淭his hasn鈥檛 been getting enough attention,鈥� says Wu. 鈥淭he problem hasn鈥檛 been getting better because we are just ignoring it.鈥�

For more see 鈥淢yth busted: dumped pills aren鈥檛 main source of drugs in sewage鈥�

This article appeared in print under the headline 鈥淒rink up, dose up鈥�