The main reason why Alzheimer’s drugs keep failing is because the brain is a relatively inaccessible and harder to test and deliver compounds. Since Alzheimer’s affects the brain, it is quite difficult for researchers and scientists to access the brain and release drugs that are on trial.
The other reason that Alzheimer’s drugs are failing is that the condition is challenging since symptoms emerge a decade or more after the onset of the disease. As a result, pharmaceutical companies have to go through expensive and lengthy trials which may eventually not pay off. Before a trial is finished, most patents will have already expired.
It’s also because the drugs currently available for treatment can only help some patients while they may not work for other patients. These drugs also don’t work for everyone and come with side effects. See some of the current Alzheimer’s drugs used to treat symptoms.
Most companies that manufacture Alzheimer’s drugs have targeted the amyloid-β proteins that form aggregates or plaque in the brain of people with Alzheimer’s.
From evidence, it is suggested that amyloid (a protein in the body) is deposited early in the course of the disease even before clinical symptoms begin appearing. This means that targeting amyloid in patients with only a mild or moderate Alzheimer’s disease leads to failed clinical trials and drugs and it may also not be enough to stop the disease from progressing.
There is little that is known about the biology of Alzheimer’s. Some companies have stopped in their pursuit of an Alzheimer’s drug due to the amount of time, energy and money needed and the continued failures.