Drugs for Alzheimer's disease

There is no cure for Alzheimer's disease, but medication can help manage the condition. Currently, the main drugs used to treat Alzheimer's are what's known as symptomatic therapies, meaning they ease symptoms but don't address the cause of the disease. These include cholinesterase inhibitors and memantine. A more recent entry into the field, lecanemab, may help slow the progression of the disease. Here's a look at how these medications work.

Cholinesterase inhibitors

One way Alzheimer's harms the brain is by decreasing levels of a chemical messenger called acetylcholine, which helps with alertness, memory, and thought processing. Cholinesterase inhibitors boost the amount of acetylcholine available to nerve cells by preventing its breakdown in the brain.

Three drugs in this category are approved by the FDA: donepezil (Aricept), galantamine (generic), and rivastigmine (Exelon). They can be prescribed at any stage of Alzheimer's, from mild to severe. The drugs are taken daily in pill form. Rivastigmine is also available as a skin patch.

These drugs can turn back the clock on memory loss, but only so far. "They can restore your memory to like it was six to 12 months before, but the drugs can't slow the disease's progression," says Dr. Andrew Budson, chief of cognitive behavioral neurology at Harvard-affiliated VA Boston Healthcare System. "And you have to keep taking the drug to maintain that advantage." People generally show the effects of the drug within one to two months.

Dr. Budson says that most people do well with any of the cholinesterase inhibitors. "However, we have the most experience with donepezil, so we usually try that one first," he says. "Galantamine is generally second-line." The drugs are covered by Medicare and well tolerated by most people. Still, common side effects include upset stomach, nausea, vivid dreams, and loose stools.

Since rivastigmine comes in a patch, it is often used for people who can't tolerate the pills. Also, people with certain types of cardiac arrhythmias shouldn't take cholinesterase inhibitors, as they can slow the heart rate.

Memantine

Another symptomatic drug approved for moderate-to-severe Alzheimer's is memantine (Namenda). It works by modulating the effects of both glutamate and dopamine, two chemicals that send messages between nerve cells in the brain and are widely involved in brain functions, including memory.

Typically, doctors prescribe memantine when a person with Alzheimer's begins showing difficulty performing activities of daily living, like dressing and bathing. "It is prescribed to help slow down the progression of symptoms, which could enable some people to maintain some daily functions a little longer than they would without the medication," says Dr. Budson.

The drug is taken as a pill or liquid once or twice a day. It may take as long as three months, or even longer, to see any improvement. Common side effects include dizziness, headache, drowsiness, confusion, and agitation.

Lecanemab

This new drug, approved by the FDA in January 2023, works differently from other Alzheimer's drugs, as it helps to slow the progression of the disease.

Lecanemab (Leqembi) is an immunotherapy that targets the protein beta-amyloid to slow the buildup of amyloid plaques in the brain. Plaques make it difficult for brain cells to communicate with one another, impeding memory and other mental functions. "The drug doesn't stop new plaque from forming, but slows the speed at which it can accumulate," says Dr. Budson.

The drug works only in people with early-stage Alzheimer's, which means they are showing mild cognitive impairment or mild dementia. "These are individuals who have trouble with thinking and memory and struggle with completing complicated tasks like paying bills and grocery shopping — but don't have problems with daily living," says Dr. Budson.

A study published Jan. 5, 2023, in The New England Journal of Medicine looked at 1,795 people who had amyloid plaques in their brains (as confirmed by MRI) and mild memory problems. The researchers found that compared with people taking an inactive treatment, those who took lecanemab for 18 months had a slower rate of cognitive decline (as measured by cognitive tests) and less amyloid in their brains.

Lecanemab is administered every other week via an hourlong infusion. It is currently unknown whether a person must take it indefinitely. The drug's main risks are brain swelling and brain bleeding, so people who take powerful blood thinners are advised against taking lecanemab. Genetic testing for an Alzheimer's risk factor gene is recommended for candidates for lecanemab, as those who have two copies of the gene may have between three and 10 times the likelihood of side effects.

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