PAX-D study: treatment resistant depression

The purpose of this study is to find out if pramipexole is a useful treatment for treatment resistant depression (TRD). A significant proportion of people diagnosed with clinical depression (up to 3 in 10) do not improve with current first-line treatments and are regarded as having TRD. Current medicines for TRD are not particularly effective for many people and often have unwanted effects which may be distressing.

There is some evidence that pramipexole may be an effective treatment for TRD. Pramipexole is unlike current antidepressant drugs in that it acts like a brain chemical called dopamine, which is known to influence people’s motivation to pursue goals and affects how rewarding they find them. This study will require visits to Oxford.

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Study for

Estudio dirigido a

Zielgrupper der Studie

Onderzoek voor:

Adults with treatment resistant depression

Sponsored by

Patrocinado por

Gesponsert von


University of Oxford








Participate by

Participar mediante


Duur van onderzoek:

May 1, 2024




What is expected of me? 

¿Qué se espera de mí?

Was wird von mir erwartet?

Wat wordt van mij verwacht?

The PAX-D study is designed to assess the effect of taking pramipexole. In order to do this, half the people in the trial will be taking pramipexole and half will be taking a placebo (a tablet that looks like pramipexole but has no effect). Overall from screening until the final visit, the study will last approximately one year for each participant. The study will involve a number of visits, described below, to the Warneford Hospital in Oxford (maps).

Screening visit

The team will ask questions about your health, mood, and medications. They will take a blood sample, and may ask for a urine sample. You will be set up to access the True Colours self-report system via the internet or your smartphone.

True Colours questionnaires

True Colours is a system that allows you to answer questionnaires about your health. Questionnaires will be sent weekly during the first 12 weeks of the study, after that the frequency will reduce. We estimate that it should take at most 15 minutes to complete the weekly questionnaires.

Randomisation visit

You will be randomly allocated either pramipexole or a placebo. The team will take your measurements and a blood sample. You will be asked to complete your True Colours questionnaire and a decision-making task on a computer.

Study medication

Following the randomisation visit the study medication will be posted to your home address (or to another suitable address, if you prefer, such as your GP practice or local pharmacy). Most participants will take their tablets at night as a single dose before bed. You will be provided with a schedule that describes how to increase your dose gradually over a period of about a month. This dose will then continue for the remainder of the study. In the event that you experience unwanted effects from pramipexole, your psychiatrist will ask you to reduce the dose to a level that is tolerable for you. At the end of the study you will be provided with a similar schedule to reduce your dose gradually over a period of around two weeks.

In between the visits described, you will be contacted regularly by a PAX-D study research assistant, usually by telephone. The research assistants will review your True Colours responses and ask about your experience of the study and the study medication

Other visits

You will be asked to attend four additional clinic visits at 2, 6, 12, and 48 weeks after you have attended the randomisation visit. At each visit measurements will be taken and you will be asked to complete a questionnaire; at weeks 2 and 12 you will be asked to perform a decision-making task.

Contact our study team

What is the benefit for me?

¿En qué me beneficia?

Welchen Nutzen habe ich davon?

Wat is het voordeel voor mij?

The purpose of the PAX-D study is to find out if pramipexole is a useful treatment for TRD. Taking pramipexole may improve your depression, but we cannot guarantee this.

You will be able to claim reasonable travel expenses, including costs of parking for study visits. Refreshments will be provided during any lengthy visits.

Who is the study for? 

¿A quién va dirigido el estudio?

Für wen ist die Studie geeignet?

Voor wie is het onderzoek bedoeld?

To take part you must have tried 2 or more anti-depressants but seen no or little improvement in mood.

You must not have a previous history of psychosis, bipolar depression, or impulse control disorders.

Pramipexole is an ‘add-on’ treatment for depression so we will ask you to continue your regular antidepressant treatment. On joining the study you should be on a stable dose of antidepressant for around 4 weeks. Wherever possible we will ask that your antidepressant not be changed for the first 12 weeks of the study (however your psychiatrist will be able to change your prescription if necessary). We will also ask that you not start a course of psychotherapy for the first 12 weeks of the study. This is allow us to assess the effectiveness of pramipexole fairly.

You will need access to a computer, smartphone or tablet to complete study questionnaires.

Complete this questionnaire to take part.

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