Anti-parkinson drugs are used to treat Parkinson disease (PD) and related syndromes ("parkinsonism"; "parkinsonian syndromes", et al).

WTF are Parkinson disease and 'parkinsonism' and 'parkinsonian syndromes' and stuff like that?

These terms are broad, encompassing many diseases that all share the component of damage to specific parts of the brain (namely the regions known as the "striatronigral pathway" and "basal ganglia"). So, it makes a lot of sense that all of these parkinsonian disorders share symptoms -- common symptoms are essential (24/7) tremor, intentioned (occurring while aiming the hand to a target) tremor, fatigue/depression, ataxia (difficulty walking), and vagal hyperhidrosis (a type of excessive sweating).

Classic Parkinson disease (PD), the one we hear of most often, strikes people during their late middle age and is of unknown biological cause. A major variant of PD is one that shows up in younger adults (e.g., Michael J. Fox's case).

Unsurprisingly, the "parkinson-" syndromes share similar features with "regular" PD. Somewhat ironically, these parkinsonian syndromes generally have a known cause, ranging from brain infection (encephalitis and the related meningitis) to head trauma to genetic syndromes to what have you. Treatment of patients with antipsychotic agents is also one way that parkinsonism can develop.

In any event, anti-parkinsonian agents may be helpful no matter what the cause of your parkinsonism is.

The crux of effective treatment of the parkinsonian disorders is the stimulation of dopaminergic neurons. Most drugs that are effective in these disorders are "pro-dopaminergic" in some way, shape, or form.

Types of antiparkinsonian agents:

The archetypal treatment, levodopa (L-DOPA in chemical shorthand; the drug is sold as DOPAR and under many other brand names).

L-DOPA combined with other drugs (a common combination is with "carbidopa" and is sold in a pill with L-DOPA with the brand name SINEMET).

Newer "dopamine agonists". These drugs are relatively new and consist of drugs that activate specific dopamine receptors. Examples include NEUPRO (rotigotine) and the non-intuitively sedating MIRAPEX and REQUIP (pramipexole and ropinirole, respectively).

Anticholinergic drugs such as the ubiquitous BENADRYL (diphenhydramine) and the prescription medicine ARTANE (trihexyphenidyl) are also used.

MAOI (Monoamine Oxidase Inhibitor) drugs, which increase the availability of serotonin, norepinephrine, and of course, dopamine, are also used to treat cases of parkinson-type stuff.