Most drugs for Parkinson’s disease mainly treat symptoms of the disease, and do not really slow down the progression of the disease. 

Take for example levodopa. This drug is converted into dopamine, which is a substance that is substantially reduced in Parkinson patients. Levodopa however does not slow down the progression of the disease; it just improves symptoms for a while. But the disease still further progresses, which also leads to increased amounts of levodopa to be given to patients. 

Another example are dopamine agonists, like pramipexole (Mirepex), ropinirole (Requip) or rotigotine (Kynmobi). These drugs stimulate dopamine receptors, but they do not address the root causes of Parkinson’s disease, like mitochondrial dysfunction, protein accumulation and oxidative stress. 

Selegiline and rasagiline a MAO-B (monoamine oxidase) inhibitor. This means it inhibits the MAO-B protein (enzyme). 

MAO-B is an enzyme that breaks down dopamine. MAO-B inhibitors inhibit this enzyme, so less dopamine is broken down, which increases dopamine levels in the brain (in Parkinson’s disease, there is a shortage of dopamine). 

However, MAO-B inhibitors like selegiline and rasagiline also seem to have neuroprotective effects (R). 

One way they can achieve this is by protecting neurons against oxidative stress. 

The MAO-B enzyme breaks down dopamine, and by doing so it produces lots of free radicals. These are small, reactive particles that damage cell structures. 

So by inhibiting MAO-B, less free radicals are produced, leading to less oxidative stress, especially in dopamine-producing cells; the same cells that get damaged with Parkinson’s disease.  

These are drugs used to treat other diseases than Parkinson’s which have been shown to reduce the risk or progression of Parkinson’s disease.

This drug is used in male patients to reduce symptoms of prostate enlargement (prostate hypertrophy). It’s an alpha-1-adrenergic receptor antagonist, meaning it blocks alpha-1-adrenergic receptors on cells. 

When these receptors are stimulated, for example on blood vessel cells or cells lining the ducts that transport urine, these vessels contract. 

By inhibiting alpha-1-adrenergic receptors, however, these vessels relax, which explains how terazosin could improve prostate hypertrophy or overgrowth, which presses on blood vessels and urine flow vessels. 

However, this drug also has been shown to be associated with less Parkinson’s disease (R,R). Various studies show that people who take this drug have less risk of Parkinson’s disease (R,R). #

This drug is used to prevent immune rejection of kidney transplants. 

Rapamycin also has been shown to extend lifespan in dozens of animal studies. Therefore, in lower doses it is taken by many longevity enthusiasts to extend lifespan and healthspan. 

Studies also show that rapamycin could be protective for Parkinson’s disease (R,R). Currently, clinical trials are ongoing using rapamycin-like drugs (“rapalogues”) to treat Parkinson’s disease (R).

Rapamycin could improve Parkinson’s disease via several mechanisms. 

Firstly, it induces autophagy. Etc etc

Mitophagy etc