What would count as a cure

Slow, stop or reverse

People mean different things by a cure. It helps to split it into steps.

• Slow it. The disease still gets worse, but more slowly. This would already change lives. It is what most trials on this site are trying to show.
• Stop it. The disease stops getting worse. People keep the abilities they have now.
• Reverse it. Lost abilities come back, because lost brain cells are replaced or repaired.
• Prevent it. People at high risk never develop Parkinson's at all.

A full cure would stop the disease and repair the damage already done. Nothing has yet been shown to do even the first step, slowing it.

Easing symptoms is not the same as slowing the disease

Today's medicines, such as levodopa, work well on symptoms like stiffness and slow movement. They replace the dopamine the brain has lost. But the brain cells keep dying underneath.

This makes slowing hard to measure. A drug that eases symptoms can make people score better for a while, even if the disease carries on as before. So trials have to be designed to tell the two apart. One way is a delayed-start trial, where some people start the drug later than others.

How we would know

A trial that can show slowing has four things.

• A placebo. Some people get a dummy treatment, so the difference is not just chance or what people expect. See placebo.
• Enough people. Often hundreds, because Parkinson's changes slowly and differs from person to person.
• Enough time. A year or more, and often much longer.
• Measures that matter. Movement, daily life and thinking, not just a blood test or a scan.

A change in a scan or a biomarker is a clue, not proof. Several drugs have changed a marker and still not helped people. Small trials without a placebo often look better than the large trials that follow.

Why it takes so long

A new drug usually goes through three stages of trials in people. Each one must finish before the next can start. The last, a Phase 3 trial, is the large one that can show slowing. Finding enough people to take part often takes longer than planned.

Then regulators review the results before a drug can be used outside trials. Even a clear success today would take time to reach clinics.

How this site measures progress

Each approach is placed on the same five steps. The steps show how far the work has got, not whether it works.

1. Step 1 Lab only
2. Step 2 First tests in people
3. Step 3 Testing whether it helps
4. Step 4 Final large trials
5. Step 5 Approved somewhere

Next to the steps, every approach also says whether it has been shown to slow Parkinson's. Today, for every approach, the answer is "not yet".

Step five, approved somewhere, does not mean a cure either. A treatment can be approved because it replaces some lost cells or eases symptoms, without stopping the disease.

What would change the answer

The answer changes when a large, well-run trial shows that a treatment slows Parkinson's. Other scientists must check the result too. When that happens, we will change this page and every approach page on the same day.

Until then, treat every claim of a cure with care. That includes claims from clinics, supplement sellers and news stories. Talk to your neurologist or Parkinson's nurse first.