Information and examples of repurposed drugs

Repurposing
A repurposed drug is one for which new uses have been discovered, sometimes by noticing and exploiting a side-effect, as with "off-label" usage, and sometimes through research, utilizing drug screening, sophisticated tools and testing.

One example of a repurposed drug that has escaped no one’s attention is Viagra. Viagra was originally developed for another purpose altogether; it first gained FDA approval as a treatment for hypertension.
 
In the realm of severe neurological disorders, an antibiotic called Ceftriaxone has been found to activate, or "turn on", the gene encoding the glutamate transporter in neurons. Drug trials are now underway to determine whether this has a neuroprotective effect on patients suffering from ALS, also known as Lou Gehrig's Disease.

Background
With Aid of Drug Library, New Remedies From Old
Teaching An Old Drug New Tricks
New Uses for Old Drugs (download PDF)
NYT - With Aid of Drug Library, New Remedies From Old

Recent examples of existing drugs that may have potential new uses for neurological diseases.

Epilepsy drug shows potential for Alzheimer's treatment

Cough medicine ingredient could effectively treat prostate cancer

Unsuccessful drug against anxiety opens a novel gateway for the treatment of cancer

Drug reverses mental retardation caused by genetic disorder - UCLA mouse study offers hope for correcting how autism disrupts brain

Dimebon significantly improves Alzheimer's symptoms

Promising new drug targets identified for Huntington's disease

Minocycline, an antibiotic, may improve symptoms of Fragile X

Diabetes drug may hold potential as treatment for epilepsy