Why you need to replace dopamine when you have Parkinson’s

Getting dopamine to your brain is important to help you start your day when you have Parkinson’s. Levodopa, a dopamine precursor (often given with a protective DDI, either carbidopa or benserazide, to help reduce nausea), is the still most effective medication for managing Parkinson’s symptoms, especially bradykinesia (slowness) and rigidity.

Levodopa treats motor symptoms like:

  • Bradykinesia (slow movement)
  • Rigidity (stiff muscles)
  • Tremor (shaking)
  • Postural instability (balance problems)
  • Shuffling walk
  • Trouble starting movements
  • Freezing episodes.

Delaying levodopa treatment can actually make overall motor function worse. Starting early can help you move better, feel better, and enjoy life more.

Why protein & amino acids can compete…

To work well, levodopa needs to be absorbed into the bloodstream through your gut and then cross into your brain. Some people experience low medication efficacy, or find the meds don’t work as well, when they have protein near their levodopa medication. For some people, their Levodopa will struggle to work when they have a milky coffee and bacon and egg brekkie with their pills. Constipation is also a big culprit for loss of medication effectiveness, if your food isn’t moving through your gut, how can the meds get to where they need to be too?

Food protein is made up of amino acids. Levodopa is structurally similar to certain amino acids and uses the same transport systems in the gut and at the blood–brain barrier to get into the bloodstream and then the brain (think of them taking the same escalator up to the brain and protein filling the steps first and pushing levodopa out of the way and to the end of the line). When you eat protein at the same time as your levodopa dose, those amino acids can also “compete” with levodopa for transport and potentially reduce the amount that gets into your brain when you want it to. 

This can lead to:

  • Delayed or reduced effectiveness of your dose (it comes on later, or that dose doesn’t work well at all)
  • “Off” periods where motor symptoms reappear or worsen sooner
  • Motor fluctuations, where the response to the medication is unpredictable. 

n.b. Importantly, the protein effect doesn’t happen in everyone, varies from person to person, and tends to be more noticeable in people with motor fluctuations.

Nausea as a side effect

Nausea is a side effect that may happen with levodopa, especially when first starting, taking levodopa without a DDI, or after dose increases.

Why does this happen? 

  1. Levodopa turns into dopamine outside the brain (levodopa is converted into dopamine by the enzyme dopa-decarboxylase). 
  2. We want this conversion to happen in the brain, but early on, some levodopa is converted to dopamine in the bloodstream and gut.
  3. That peripheral dopamine:
    • Stimulates the chemoreceptor trigger zone (CTZ) in the brainstem
    • The CTZ sits outside the blood–brain barrier and is very sensitive to dopamine
    • This activates the nausea and vomiting reflex

Research estimates vary depending on the study setting, but in clinical and observational studies, nausea with levodopa commonly occurs in around only ~6% to ~19% of people. So addressing this for everyone living with Parkinson’s is not a one-size-fits-all approach.

Some quick tips

  • Take your carbidopa-levodopa on an empty stomach with a full glass of water if tolerated.
  • If nausea occurs, take medication with something low in protein, like a dry biscuit or toast.
  • Avoid protein at least 30 minutes before or take your pills 60 minutes after eating or drinking protein.
  • Vitamin C seems to help how the body absorbs and processes levodopa in some people. Try 1-2 tbsp of freshly squeezed lemon in your glass of water.
  • Ginger (ginger tea or ginger biscuits) can help settle your stomach for some people.
  • Your GP or neurologist can prescribe anti-nausea medication that’s safe with levodopa if needed. n.b.: Don’t independently take over-the-counter anti-nausea drugs without checking — some are unsafe in Parkinson’s.
  • Track your OFFs & ONs with when you take your pills and what you eat, there may be some foods/drinks that affect you more than others.
  • If you experience dramatic “offs” with protein, rather than eliminating it, some people shift most of their daily protein to the evening so daytime doses aren’t competing with a protein load. Ask your Parkinson’s Nurse, Dietitian or GP to help you plan a Protein Redistribution Diet. n.b. Protein is essential for muscle, immune function, energy and overall health, especially important in Parkinson’s, so don’t cut it out entirely (healthy proteins pictured).
  • Look for “on/off” patterns E.g., does the medication take longer to work after a high-protein meal? Does it wear off more quickly?
  • Work with your neurologist and bring your tracking notes to appointments. They can help adjust dose, timing or which combination is best for you based on your body’s data.

How to track when levodopa is working

Keeping a simple tracking system helps you and your neurologist optimise your medication:

Track daily response

Used our medication planner or app to record:

  • Time taken
  • Dose size
  • Time you start to feel benefits (“on” time)
  • Time symptoms return (“off” time)
  • Side effects (nausea, dizziness, dyskinesia)

This helps identify patterns related to meals, timing and activity. It can help you and your care partner plan your days. Exercise and do high-input activities during ‘on’ periods. 

Who to ask for support in Australia

Parkinson’s Organisations

These groups offer education, nurse helplines, support groups, dietitian referrals and medication guidance:

  • Parkinson’s Australia infohub – information, resources and referral guidance. 

  • State Parkinson’s organisations (NSW, QLD, SA, WA, TAS, VIC) — they often have Parkinson’s Nurse Specialists, can point you to a local dietitian and support group resources.

  •  An accredited dietitian can give you personalised advice on timing meals and protein

Your Care Team

  • Neurologist / movement disorder specialist — adjusts your Parkinson’s meds.

  • GP — for general health, nausea management and diet referrals.

  • Accredited dietitian — personalised advice on timing meals and protein so meds work best. Go to Dieitians Australia to find one near you.

  • Parkinson’s Nurse Specialist — ongoing support and education.

Key takeaways

  • Protein and levodopa use similar transport systems, and eating protein too close to medication can reduce effectiveness for some people. 

  • Adjusting meal timing and possibly shifting protein to later in the day can help maximise “on” time. 

  • Nausea can often be eased with small snacks, fluids, and medical help if needed. 

  • Tracking your symptoms and response to medications and foods helps personalise your treatment.

  • Support from neurologists, dietitians and Parkinson’s organisations in Australia can make a big difference. 

Resources & references 

Rusch, C., Flanagan, R., Suh, H., & Subramanian, I. (2023). To restrict or not to restrict? Practical considerations for optimizing dietary protein interactions on levodopa absorption in Parkinson’s disease. npj Parkinson’s Disease, 9(1), 98.

Education is Medicine www.educationismedicine.com

Parkinson’s Canada Factsheet https://www.parkinson.ca/wp-content/uploads/Levodopa-and-Protein-Medication-Absorption-Concerns.pdf

Parkinson School https://www.parkinson-school.com/

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