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A Study of Candesartan Compared to Placebo in Adults with Episodic Cluster Headache to Prevent Severe Headache Attacks

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What is this trial about?

A plain-language summary of the goals, design and what participants do

This study is looking at episodic cluster headache, a condition where people experience severe headache attacks that occur in patterns or cycles called bouts. The treatment being tested is candesartan, a medication that is normally used to treat high blood pressure but is being studied here to see if it can help prevent cluster headache attacks. Participants will receive either candesartan tablets or placebo, and both will be given in capsules so that no one knows which treatment they are receiving. The purpose of the study is to find out if candesartan can reduce the number of severe and very severe cluster headache attacks compared to placebo during a three-week treatment period.

The study involves several phases that participants will go through over time. First, there is a one-week period before treatment starts where participants keep a diary of their headache attacks to establish a starting point. Then comes a three-week blinded phase where participants take either candesartan up to 32 milligrams daily or placebo, with neither the participants nor the doctors knowing which treatment is being given. During this time, participants continue to record their headache attacks, how severe they are, and what medications they use to treat them. After the three-week blinded phase, there is an optional treatment period where participants may continue taking the study medication, followed by a wash-out phase where the medication is stopped to see what happens.

Throughout the study, participants will be asked to complete questionnaires about how much their condition has improved, how the headaches affect their daily life, and how they are feeling emotionally. The study will track how often severe and very severe attacks occur, how intense the attacks are, and how much rescue medication participants need to use. Researchers will also monitor how long it takes for attacks to stop completely and whether attacks return after treatment ends. The study is designed to gather information about whether candesartan can effectively prevent cluster headache attacks and improve the quality of life for people living with this condition.

The research process

The trial runs in 5 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Baseline diary period

    This period lasts one week before receiving any treatment.

    During this time, you will record all your headache attacks in a diary.

    You must experience between 4 attacks per week and a maximum of 8 attacks per day of severe or very severe intensity on average.

    This information will be used to compare with your headache frequency during the treatment period.

  2. Step 2

    Blinded treatment phase

    This phase lasts three weeks.

    You will be randomly assigned to receive either candesartan 32 mg or placebo (an inactive substance that looks like the real medication).

    Candesartan is a medication that blocks certain receptors in the body and may help reduce the frequency of severe headache attacks.

    The medication is taken by mouth in the form of encapsulated tablets.

    Neither you nor your doctor will know which treatment you are receiving during this period.

    You will continue to record all your headache attacks, their intensity, and any medications you use to treat them.

  3. Step 3

    Open treatment phase

    This phase follows the blinded treatment phase.

    During this period, you will receive candesartan treatment, and both you and your doctor will know what medication you are taking.

    The duration of this phase will be specified by your study doctor.

    You will continue to monitor and record your headache attacks and any treatments you use.

    If you were free from attacks at the end of the blinded phase, the study will track when or if your severe attacks return.

  4. Step 4

    Wash-out phase

    This phase occurs after the open treatment phase if you were taking candesartan during that period.

    You will stop taking the study medication.

    The purpose is to observe if and when your severe headache attacks return after stopping the medication.

    You will continue to record any headache attacks during this time.

  5. Step 5

    Assessment visits

    Throughout the study, you will complete questionnaires at specific time points: at week 3, week 9, and week 14 after the baseline period.

    These questionnaires will ask about your overall improvement, how your headaches affect your daily life, and your mood.

    You will rate how much better you feel compared to before starting the treatment.

    Questions about your emotional well-being, including anxiety and depression symptoms, will be included.

    You will also be assessed for any thoughts related to self-harm using a specific questionnaire.

    At week 8 of the open treatment phase, you will rate your overall condition compared to the end of the blinded treatment phase.

Who can join the trial?

9 criteria

  • You must be between 18 and 70 years old when you sign the consent form to join the study
  • You must have episodic cluster headache, which is a type of severe headache that occurs in patterns or cycles, with pain-free periods in between
  • You must have had at least one previous period of cluster headache that lasted more than 5 weeks
  • If you have other types of headaches such as migraine (a headache disorder causing severe throbbing pain) or tension-type headache (a headache causing mild to moderate pressing or tightening pain), you must be able to clearly tell them apart from your cluster headache attacks based on how the pain feels and other symptoms you experience
  • During the one-week observation period before treatment starts, you must have between 4 attacks per week and a maximum of 8 attacks per day that are severe or very severe in intensity on average
  • Your current period of cluster headache attacks must be typical of what you usually experience during these episodes
  • If you are a woman who can become pregnant, you must not be pregnant or planning to become pregnant during the study, and you must use an approved method of birth control throughout the study
  • If you are a man, no birth control requirements are needed
  • You must be able to understand and sign the consent form, and follow all the requirements and rules of the study

Who cannot join the trial?

4 criteria

  • The study information does not list specific reasons why patients cannot participate in this clinical trial
  • If you are interested in participating, you will need to discuss with the study team to learn about any health conditions, medications, or other factors that might prevent you from joining
  • General exclusion reasons in clinical trials may include having certain other medical conditions, taking medications that could interfere with the study drug, being pregnant or breastfeeding if you are a woman of childbearing age, or having allergies to the study medication
  • The study drug being tested is called candesartan, which is a type of medicine called an angiotensin-receptor antagonist that affects blood pressure regulation in the body
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Investigated drugs

Candesartan is a medication that belongs to a group of medicines called angiotensin-receptor antagonists. In this study, it is being tested to see if it can help prevent cluster headache attacks. The medicine works by blocking certain substances in the body that can affect blood vessels. It is being compared to a placebo to find out if it can reduce how often severe cluster headaches occur in people who have episodic cluster headaches.

What is already known about the treatment

Candesartan – Candesartan is a medication that belongs to a group of drugs called angiotensin-receptor antagonists, which work by blocking certain chemicals in the body that cause blood vessels to tighten, allowing blood vessels to relax and widen instead. It is commonly approved and used to treat high blood pressure and heart failure, but is currently being studied in clinical trials to see if it can help prevent severe cluster headache attacks in people who experience these intense headaches in episodes. In this research study, participants take candesartan as a tablet by mouth at a dose of 32 mg daily to test whether it can reduce the number of severe headache attacks compared to a placebo (inactive pill). The medication works at the molecular level by blocking receptors for a substance called angiotensin II, which normally causes blood vessels to narrow, and this blocking action may help prevent the painful headache episodes by affecting blood flow and other processes involved in cluster headaches.

Investigated diseases

Episodic Cluster Headache – Episodic cluster headache is a neurological condition characterized by recurring periods of severe headache attacks that occur in cyclical patterns or clusters. During an active period, called a cluster bout, individuals experience multiple headache attacks that typically last between 15 minutes to 3 hours. These attacks occur with remarkable regularity, often striking at the same time each day, and are usually felt on one side of the head, commonly around or behind the eye. The pain is described as extremely intense and sharp, often accompanied by symptoms such as watering of the eye, nasal congestion, or facial sweating on the affected side. Between cluster periods, individuals may experience remission phases lasting months or even years when no headaches occur. The episodic form is distinguished from chronic cluster headache by these pain-free remission periods that last at least three months.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2025-521470-34-00Protocol codeE. CandClus2 V3Estimated enrolment83 patientsSponsorHelse Bergen HF

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