Ecstasy and anti-depressant drugs such as Prozac have the potential to stop cancer cell growth, research has found.
A University of Birmingham team tested the impact of amphetamine derivatives such as Ecstasy and weight-loss pills, and antidepressants including Prozac.
They found the drugs were effective at blocking cancer growth in more than half of lymphoma (white blood cell cancer) samples tested.
It is hoped the FASEBJ Journal study will will lead to new cancer therapies.
The study focused on 17 samples of acute lymphoblastic leukaemia and multiple myeloma.
Cancer growth was slowed down in nine out of the 17 samples when they were exposed to antidepressants, and in 11 out of 17 when exposed to one or both of the amphetamine derivatives.
Researcher Professor John Gordon said: "We think that a range of psychotropic agents that are being used, or sometimes abused, for other reasons will now help us in our fight against all different types of cancer.
"We are excited that drugs like Prozac are effective in killing these types of cancer cells, as these antidepressants are in such wide circulation and have an impressive safety record."
However, the researchers stressed that the use of ecstasy was not so straightforward - the dose required to block cancer growth was so high it would kill the patient.
Dr Nick Barnes, who also worked on the study, said he was still hopeful the drug could be one day be used to combat cancer.
"Perhaps by breaking down the actions of this designer drug we can extract its cancer killing properties from more general toxic effects associated with its use.
The research was supported by the Leukaemia Research Fund. Spokesman Dr David Grant welcomed the findings.
He said: "Around 10,000 people are diagnosed with a lymphoma in the UK each year and so the possibility that some of these patients can be treated with antidepressants that have cancer-killing properties is truly remarkable.
"Clearly there is a lot more work to do before this became a reality but it is very exciting that there may be other, much less aggressive ways, of treating this particular cancer."