AuthorisedTherapeutic exploratory (Phase II)Interventional

Evaluation of the effect of botulinum toxin on refractory upper limb rest tremor in parkinsonian patients, double-blind, placebo-controlled cross-over study : TOX PARK

Tremors in the hands and arms are a common and frustrating symptom of Parkinson’s disease, especially when resting. For some people, standard Parkinson's medicines do not bring enough relief. This trial, called TOX PARK, is testing whether injections of botulinum toxin into arm muscles can safely reduce these stubborn tremors. In this study, participants will receive both the real medicine and an inactive saltwater injection (placebo) at different times. To keep participants comfortable during the injections, a pain-relieving gas called Entonox (commonly known as gas and air) will be available. Researchers will assess your tremors, hand grip strength, and quality of life six weeks after each injection. By comparing how you feel after both treatments, the study team hopes to find out if botulinum toxin can help people with Parkinson's manage tremors that are hard to treat.

At a glance

Status

Authorised

Phase

Therapeutic exploratory (Phase II)

Sponsor

Centre Hospitalier Universitaire De Toulouse

Enrolment target

Start

24 Jul 2026

parkinson disease

What is this study about?

Parkinson’s disease affects the brain and nerves, often causing involuntary shaking known as a resting tremor. This shaking usually happens when the hands or arms are relaxed. While regular Parkinson’s tablets help many people manage their symptoms, some people find their tremors do not improve enough. When standard treatments fail to work, tremors are called 'treatment-resistant' or 'refractory'.

The TOX PARK study is exploring a different approach using botulinum toxin (Dysport). Botulinum toxin works by temporarily interrupting the chemical signals between nerves and muscles, helping overactive muscles relax. While it is already widely used for various nerve and muscle conditions, researchers want to see if precise injections can calm troublesome arm tremors in Parkinson's.

To make sure the results are reliable, this trial is a 'placebo-controlled cross-over' study. This means you will receive both the real medicine and an inactive dummy injection (saline) at separate times, without you or your doctor knowing the order. Comparing the two treatments in the same person gives scientists the clearest possible picture of how well the medicine works.

Finding a reliable way to reduce stubborn tremors could make a significant difference to everyday life. Calming hand tremors can make daily tasks—like drinking from a cup, eating, writing, or using a mobile phone—much easier, helping people maintain their independence and confidence.

Key takeaways

Tests botulinum toxin injections for Parkinson’s hand tremors that have not responded to usual tablets.
A cross-over trial where every participant receives both the medicine and a dummy injection at different times.
Pain-relieving gas (Entonox) is provided during the injections to help keep you comfortable.
Follow-up visits at six weeks will measure tremor relief, grip strength, and quality of life.
Taking part is completely voluntary and you can withdraw at any time.

Who may be eligible?

This trial is designed for adults aged 18 and over who have been diagnosed with Parkinson’s disease and experience a resting tremor in their hand or arm.

To take part, your tremor must be considered 'treatment-resistant'. This means you have already tried standard Parkinson’s tablets, but they have not provided enough control over your hand or arm shaking. Both men and women are welcome to apply.

You may not be eligible if you have other medical conditions that cause muscle weakness, allergies to botulinum toxin, or if your doctor feels the injections would not be safe for you. The study team will carry out a thorough health check to confirm whether the trial is a good fit.

Could this study suit you?

Answer these quick questions to see if you may be eligible. This is a guide only — the research team makes the final call.

I am aged 18 or older.
I have a confirmed diagnosis of Parkinson’s disease.
I have an involuntary shaking (resting tremor) in my hand or arm.
My tremor has not improved enough with regular Parkinson’s medicines.
I am able to attend hospital clinic appointments for injections and follow-up checks.

Answer every question to see your result.

What does participation involve?

Taking part involves several visits to the hospital clinic. During treatment visits, a specialist doctor will give small injections into specific muscles in your arm. To help reduce any discomfort, you will be offered Entonox (gas and air) to breathe in during the procedure. Because this is a cross-over study, you will receive the real medicine at one stage and an inactive saltwater injection at another, with a waiting period in between. Six weeks after each injection, you will return to the clinic for follow-up assessments. During these visits, doctors will measure the shaking in your arm, test your hand grip strength using a small measuring device, and ask you to complete short questionnaires about your daily activities, mood, and overall quality of life. The study team will monitor you closely throughout the trial to track any changes or side effects.

Potential risks and benefits

The main potential benefit is a reduction in your arm tremor, which could make everyday tasks easier and improve your quality of life, although improvement cannot be guaranteed. The most common risk of botulinum toxin injections in the arm is temporary muscle weakness in the treated hand, which could affect your grip. You might also feel brief pain, bruising, or soreness where the needle enters the skin. Taking part is entirely voluntary, and you can change your mind and leave the study at any time without your standard NHS medical care being affected.

Locations (1)

Some site locations are approximate. We're improving this — please verify with the trial team before travelling.

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Unverified
France

Common questions

What is botulinum toxin?

Botulinum toxin is a prescription medicine that temporarily relaxes muscles by blocking nerve signals. It is widely used in the NHS to treat various muscle spasms and movement conditions.

Will the injections be painful?

You may feel a brief pinch or sting. To keep you comfortable, the study provides Entonox (gas and air), a fast-acting pain relief gas that you can breathe in during the injections.

What does a cross-over study mean?

It means every participant gets to try both the real treatment and the dummy (placebo) injection at different stages of the trial, allowing researchers to compare the results fairly.

Could the treatment make my hand weak?

Temporary weakness in the treated hand is a known side effect of botulinum toxin. The study team will carefully measure your grip strength at each visit to check for this.

Can I keep taking my normal Parkinson's medications?

Usually, yes. You will need to discuss your exact medication routine with the study doctors to make sure your doses remain steady during the trial.