A commonly used anti-diarrhoea drug, available in chemists around the world, could offer new hope for a treatment for autism spectrum disorder (ASD).
Researchers believe anti-diarrhoea medication loperamide has the potential to treat the core social symptoms of ASD.
The surprising find came from computer analysis of existing drugs to see which ones might affect proteins involved in ASD.
"There are no medications currently approved for the treatment of social communication deficits, the main symptom in ASD," said Dr Elise Koch, of the University of Oslo and the study's lead author.
"However, most adults and about half of children and adolescents with ASD are treated with antipsychotic drugs, which have serious side effects or lack efficacy in ASD."
The researchers said that the reason a medication so seemingly unrelated to ASD could offer treatment is due to how it works in the body.
Loperamide binds to and activates a protein called the μ-opioid receptor, which is normally affected by opioid drugs, such as morphine.
The receptor also affects social behaviour, and in previous research, genetically-engineered mice that lack the μ-opioid receptor demonstrated social deficits similar to those seen in ASD.
Drugs that activate the μ-opioid receptor helped to restore social behaviours, the researchers said.
These results in mice highlight the tantalising possibility that loperamide, or other drugs that target the μ-opioid receptor, may represent a new way to treat the social symptoms present in ASD.
The researchers warned that further work was required to test this hypothesis.
They turned to drug repurposing, which involves exploring existing drugs as potential treatments for a different condition.
The approach has plenty of benefits, as there is often extensive knowledge about existing drugs in terms of their safety, side-effects and the biological molecules that they interact with in the body.
The researchers used a computer-based protein interaction network. Such networks look at proteins and the complex interactions between them.
The researchers constructed a protein interaction network that included proteins associated with ASD.
By investigating existing drugs and their interaction with proteins in the network, the team identified several candidates that counteract biological process underlying ASD - the most promising of which was loperamide.
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