The motor symptoms of Parkinson's disease (PD) are caused primarily by degeneration of dopaminergic neurons in the substantia nigra. The nonmotor symptoms of the disease are thought to be caused by degeneration of other neurotransmitter systems. No disease-modifying drugs are available for treatment of PD.

Cannabis (marijuana) contains more than 60 pharmacologically active cannabinoids; delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) are the best known. THC is the main psychoactive constituent of cannabis. CBD, unlike THC, does not produce intoxication or euphoria.

Tetrabenazine (Xenazine - Ovation Pharmaceuticals), an old drug first synthesized 50 years ago for treatment of schizophrenia, was recently approved by the FDA for the treatment of chorea associated with Huntington's disease. It has been available in other countries for decades.

Pregabalin (Lyrica - Pfizer) is the first drug approved by the FDA for management of fibromyalgia. When it was first marketed, pregabalin, which is structurally similar to gabapentin (Neurontin, and others), was approved for treatment of neuropathic pain associated with postherpetic neuralgia and diabetic peripheral neuropathy and for adjunctive treatment of partial onset seizures in adults with epilepsy. It has also been prescribed off-label for other types of neuropathic pain such as sciatica.

Over-the-counter products containing melatonin are widely used as sleep aids in children and adults.

Deep brain stimulation (DBS) is increasingly used to treat advanced Parkinson's disease (PD), but few controlled clinical trials have been published. New evidence from a large controlled study has recently become available.

View the Comparison Table: Some FDA-Approved Drugs for Weight Management

View the Comparison Table: Some Oral Antiseizure Medications

A selective serotonin reuptake inhibitor (SSRI) is generally used for initial treatment of major depressive disorder (MDD). A serotonin-norepinephrine reuptake inhibitor (SNRI), bupropion (Wellbutrin SR, and others), and mirtazapine (Remeron, and others) are reasonable alternatives. Improvement in symptoms can occur within the first two weeks of treatment with these drugs, but a substantial benefit may not be achieved for 4-8 weeks.

The FDA has approved deutetrabenazine (Austedo – Teva), a vesicular monoamine transporter 2 (VMAT2) inhibitor, for treatment of chorea associated with Huntington's disease and, more recently, for treatment of tardive dyskinesia in adults. It is the second VMAT2 inhibitor to be approved for each of these indications; tetrabenazine (Xenazine, and generics) was approved earlier for Huntington's chorea and valbenazine (Ingrezza) was recently approved for treatment of adults with tardive dyskinesia.