New Tests on Effects of THA Urged

The jury is still out on THA, the experimental drug being tested as a treatment for Alzheimer’s disease. Although researchers have faulted Dr. William K. Summers’ work on the subject, most seem to agree that the drug may hold promise and should be tested.

THA, also known as tacrine, was synthesized during World War II by researchers looking for an intravenous, anti-bacterial agent to treat soldiers, Summers said. But it turned out to be more effective at arousing the central nervous system.

Among other things, it proved useful in reversing coma caused by drug overdose. According to Summers, researchers used it in Great Britain in the 1950s to prevent respiratory depression in cancer patients who were on morphine.


In the 1960s, researchers at the Missouri Institute of Psychiatry used THA in looking for the causes of schizophrenia. They would use drugs to induce delirium in subjects and, when necessary, reverse it with THA.

The drug is believed to work in part by slowing the breakdown of a chemical in the brain that plays a crucial role in memory. That chemical, acetylcholine, has been found to be deficient in patients with Alzheimer’s disease.

THA came to Summers’ attention in the mid-1970s when he was completing his psychiatric training at Washington University in St. Louis. He was confronted one day with a patient in a delirious state, which he determined was a side-effect of a drug she had been given.

That drug, atropine, is known to block the effects of acetylcholine (the chemical deficient in Alzheimer’s patients). To treat the woman, Summers administered a drug related to THA. It reversed her condition, but there were side effects: She vomited on Summers.

Looking for a safe but effective substitute, he returned to the medical library and stumbled upon THA. Then he applied for federal permission to begin testing the drug as a treatment for overdose coma. According to Summers, it worked.

Next, Summers decided to try the drug on patients with Alzheimer’s disease.