The primary pathology of Parkinson's disease involves a reduction in dopamine, a neurotransmitter crucial for regulating movement and mood. Many medications, both prescription and over-the-counter (OTC), can either directly block dopamine receptors, deplete dopamine stores, or dangerously interact with Parkinson's medications designed to increase dopamine. A patient's unique medication schedule is also crucial, and delays in administering Parkinson's drugs can have serious consequences.
Dopamine-Blocking Culprits: Antipsychotics and Antiemetics
Why are they problematic?
Many common antipsychotic and anti-nausea medications work by blocking dopamine D2 receptors in the brain. For a person with PD, whose symptoms are caused by a dopamine deficiency, this antagonism can significantly worsen tremors, rigidity, and bradykinesia (slow movement). Some of these drugs are known to cause drug-induced parkinsonism, a condition that mimics PD, and are particularly dangerous for those with the disease.
Medications to avoid include:
- Typical Antipsychotics: Haloperidol (Haldol), chlorpromazine (Thorazine), fluphenazine (Prolixin), thioridazine (Mellaril), and pimozide (Orap) are strong dopamine blockers.
- Atypical Antipsychotics: Some second-generation antipsychotics, though generally having a lower risk, can still worsen PD symptoms. Risperidone (Risperdal), olanzapine (Zyprexa), and aripiprazole (Abilify) should be used with extreme caution.
- Antiemetics (Anti-Nausea): Metoclopramide (Reglan) and prochlorperazine (Compazine, Stemetil) are potent dopamine blockers and should be avoided.
Safer Alternatives
For managing psychosis in PD, atypical antipsychotics with lower dopamine-blocking activity are preferred under specialist supervision. These include clozapine (Clozaril) and quetiapine (Seroquel). Pimavanserin (Nuplazid) is specifically approved for PD psychosis and is a serotonin inverse agonist, avoiding dopamine blockade. For nausea, domperidone (Motilium) and ondansetron (Zofran) are generally considered safer options, though ondansetron is contraindicated with apomorphine.
Dangerous Interactions with MAO-B Inhibitors
Monoamine oxidase B (MAO-B) inhibitors, such as selegiline (Eldepryl, Zelapar), rasagiline (Azilect), and safinamide (Xadago), are prescribed to block the enzyme that breaks down dopamine, thereby prolonging its effects. However, these drugs can cause dangerous interactions with other medications, leading to a potentially life-threatening condition called serotonin syndrome or hypertensive crisis.
Medications to avoid with MAO-B inhibitors include:
- Narcotics/Analgesics: Meperidine (Demerol), tramadol (Ultram), methadone (Dolophine), and propoxyphene (Darvon) carry a risk of serotonin syndrome.
- Antidepressants: Non-selective MAOIs (phenelzine, tranylcypromine) and certain selective serotonin reuptake inhibitors (SSRIs) like fluoxetine or sertraline can lead to serotonin syndrome. St. John's Wort, an herbal supplement, also interacts and should be avoided.
- Cold and Allergy Medications: Over-the-counter decongestants like pseudoephedrine and phenylephrine, as well as cough suppressants containing dextromethorphan, can cause a dangerous increase in blood pressure.
- Muscle Relaxants: Cyclobenzaprine (Flexeril) can cause severe reactions with MAO-B inhibitors, including high fever and seizures.
Over-the-Counter and Other Prescription Medications
Beyond those with direct dopamine or MAO-B inhibitor interactions, other medications can pose risks for people with PD. These often increase specific side effects that are already common in PD, such as confusion, balance issues, or constipation.
Additional medications to approach with caution:
- Antihistamines: Older, first-generation antihistamines, like diphenhydramine (Benadryl), can cause sedation, confusion, and urinary retention. Newer antihistamines are often safer.
- Certain Blood Pressure Drugs: Methyldopa can affect the conversion of levodopa to dopamine, reducing its effectiveness. Reserpine depletes dopamine stores, which can worsen motor symptoms.
- Anticonvulsants: Certain anticonvulsants, like valproic acid, have been reported to induce or worsen parkinsonism.
- Calcium Channel Blockers: Some, particularly flunarizine and cinnarizine (less common in the US), can cause drug-induced parkinsonism.
The Impact of Supplements and Diet
Non-prescription supplements and dietary choices can also interfere with PD medication efficacy, especially with levodopa/carbidopa (Sinemet).
- Iron Supplements: Iron can bind to levodopa and carbidopa, reducing their absorption and effectiveness. It's recommended to take iron supplements at least two hours apart from levodopa.
- 5-HTP (5-hydroxytryptophan): This supplement, used for depression, can interact dangerously with carbidopa/levodopa and has been linked to a severe skin condition.
- High Protein Meals: Large amounts of dietary protein can compete with levodopa for absorption in the intestine and for transport into the brain. Timing protein intake later in the day or distributing it evenly can help.
Comparison of Problematic vs. Safer Alternatives
| Medication Category | Problematic Medications to Avoid | Generally Safer Alternatives (Consult a Doctor) |
|---|---|---|
| Antipsychotics | Haloperidol, risperidone, olanzapine, typical antipsychotics | Clozapine, quetiapine, pimavanserin |
| Antiemetics | Metoclopramide (Reglan), prochlorperazine (Compazine) | Domperidone, ondansetron (except with apomorphine) |
| Cold & Flu (OTC) | Pseudoephedrine, phenylephrine, dextromethorphan | Acetaminophen, saline nasal spray |
| Pain Medication | Meperidine (Demerol), tramadol (Ultram) | Acetaminophen, other pain relievers approved by neurologist |
| Antidepressants | Non-selective MAOIs (phenelzine), St. John's Wort | SSRIs (with caution), SNRIs, mirtazapine (under specialist guidance) |
| Blood Pressure | Reserpine, methyldopa | ACE inhibitors, ARBs, beta-blockers (under specialist guidance) |
Conclusion
Navigating medications with Parkinson's disease is a delicate process that requires vigilance and open communication with your healthcare team. Many medications that treat common ailments can interfere with the brain's dopamine system, either by blocking receptors or creating dangerous interactions with prescribed PD drugs. Before taking any new medication, supplement, or even an over-the-counter remedy, it is vital to consult your neurologist or a specialized pharmacist to confirm its safety. Awareness of these potential pitfalls is a crucial step in managing the condition and maintaining quality of life.
For more detailed information, the American Parkinson Disease Association offers resources on this topic. https://www.apdaparkinson.org/living-with-parkinsons-disease/treatment-medication/meds-to-avoid/
