Medication can be used to improve the main symptoms of Parkinson's disease, such as shaking (tremors) and movement problems.
However, not all the medications available are useful for everyone, and the short- and long-term effects of each are different.
Three main types of medication are commonly used:
- dopamine agonists
- monoamine oxidase-B inhibitors
Your specialist can explain your medication options, including the risks associated with each medication, and discuss which may be best for you. Regular reviews will be required as the condition progresses and your needs change.
Read on to learn about the treatments you may be offered. You can also see a summary of the pros and cons of treatments for Parkinson's disease, where you can compare your options.
Most people with Parkinson's disease eventually need a medication called levodopa.
Levodopa is absorbed by the nerve cells in your brain and turned into the chemical dopamine, which is used to transmit messages between the parts of the brain and nerves that control movement.
Increasing the levels of dopamine using levodopa usually improves movement problems.
It is usually taken as a tablet or liquid, and is often combined with other medication, such as benserazide or carbidopa.
These medications stop the levodopa being broken down in the bloodstream before it has a chance to get to the brain.
They also reduce the side effects of levodopa, which include:
- feeling sick (nausea) or vomiting
If you're prescribed levodopa, the initial dose is usually very small and will be gradually increased until it takes effect.
At first, levodopa can cause a dramatic improvement in the symptoms.
However, its effects can be less long-lasting over the following years – as more nerve cells in the brain are lost, there are fewer of them to absorb the medicine. This means the dose may need to be increased from time to time.
Long-term use of levodopa is also linked to problems such as uncontrollable, jerky muscle movements (dyskinesias) and "on-off" effects, where the person rapidly switches between being able to move (on) and being immobile (off).
Dopamine agonists act as a substitute for dopamine in the brain and have a similar but milder effect compared with levodopa. They can often be given less frequently than levodopa.
They are often taken as a tablet, but are also available as a skin patch (rotigotine).
Sometimes dopamine agonists are taken at the same time as levodopa, as this allows lower doses of levodopa to be used.
Possible side effects of dopamine agonists include:
- nausea or vomiting
- tiredness and sleepiness
Dopamine agonists can also cause hallucinations and increased confusion, so they need to be used with caution, particularly in elderly patients, who are more susceptible.
For some people, dopamine agonists have been linked to the development of compulsive behaviours, especially at high doses, including addictive gambling and an excessively increased libido.
Talk to your healthcare specialist if you think you may be experiencing these problems.
As the person themselves may not realise the problem, it's key that carers and family members also note any abnormal behaviour and discuss it with an appropriate professional at the earliest opportunity.
If you're prescribed a course of dopamine agonists, the initial dose is usually very small to prevent nausea and other side effects.
The dosage is gradually increased over a few weeks. If nausea becomes a problem, your GP may prescribe anti-sickness medication.
A potentially serious, but uncommon, complication of dopamine agonist therapy is sudden onset of sleep.
This generally happens as the dose is being increased and tends to settle once the dose is stable.
People are usually advised to avoid driving while the dose is being increased in case this complication occurs.
Monoamine oxidase-B inhibitors
Monoamine oxidase-B (MAO-B) inhibitors, including selegiline and rasagiline, are another alternative to levodopa for treating early Parkinson's disease.
They block the effects of an enzyme or brain substance that breaks down dopamine (monoamine oxidase-B), increasing dopamine levels.
Both selegiline and rasagiline can improve the symptoms of Parkinson's disease, although their effects are small compared with levodopa. They can be used alongside levodopa or dopamine agonists.
MAO-B inhibitors are generally very well tolerated, but can occasionally cause side effects, including:
- abdominal pain
- high blood pressure
Catechol-O-methyltransferase (COMT) inhibitors are prescribed for people in later stages of Parkinson's disease. They prevent levodopa from being broken down by the enzyme COMT.
Side effects of COMT inhibitors include:
- nausea or vomiting
- abdominal pain
Want to know more?
Parkinson's UK: drug treatments
Parkinson's UK: Parkinson's drugs and compulsive behaviours
When Parkinson's symptoms become difficult to control with tablets alone, a number of other treatments can be considered.
A dopamine agonist called apomorphine can be injected under the skin (subcutaneously) either by:
- a single injection, when required
- a continuous infusion using a small pump carried around on your belt, under your clothing, or in a bag
If you have severe on-off fluctuations, a type of levodopa called duodopa may be used.
This medication comes as a gel that's continuously pumped into your gut through a tube inserted through your abdominal wall.
There's an external pump attached to the end of the tube, which you carry around with you.
About 25 specialist neuroscience centres in the UK offer this treatment. This treatment is only available if you have very severe on-off fluctuations or involuntary movements.