• Age ≥18 years at the time of consent.

• Diagnosis of new IIH by consensus criteria, including normal structural brain imaging (excluding features of raised ICP and incidentalomas), including either magnetic resonance venography or computed tomographic venography to exclude thrombosis and no evidence of a secondary causes of raised ICP.

• Newly diagnosed patients with screening commenced no more than 4 weeks after the diagnostic LP.

• Lumbar puncture opening pressure ≥25 cm cerebrospinal fluid (CSF) at diagnosis.

• Presence of bilateral papilloedema (Frisén grade ≥1). Verification of papilloedema by the OCT Reading Centre. Where there is uncertainty fundus photography and/or ultrasound scan (B scan) of the optic nerves should be conducted for evaluation by the Independent Adjudication Committee (IAC).

• Perimetric Mean Deviation defined as between -2 to -7 decibels (dB) in at least one eye. Eyes meeting this criterion will defined as 'study eyes'.

• Reproducible visual loss present on automated perimetry including no more than 15% false positive responses (reliability confirmed by the Visual Field Reading Centre) in study eyes.

• Two or more headache days over the 7-day period prior to screening and also the patient must meet this criterion during the 7-day screening period.

• Females of childbearing potential must have a negative pregnancy test and must agree to use a highly effective birth control method (failure rate less than 1% per year when used consistently and correctly) during the whole trial duration including the last follow-up visit (12 weeks after ceasing drug). Female patients who are lactating must agree to stop breast-feeding OR Female patients of non-childbearing potential (defined as pre-menopausal females with a documented tubal ligation or hysterectomy; or post-menopausal females defined as 12 months of amenorrhoea \[in questionable cases a blood sample with simultaneous follicle stimulation hormone 25-140 IE/L and oestradiol \<200 pmol/L is confirmatory\]).

⁃ Male patients with a female partner of childbearing potential must commit to practice methods of contraception (e.g., condom, vasectomy) and abstain from sperm donation during the trial including the last follow-up visit (12 weeks after ceasing drug). Their partners, if they are women of childbearing potential, must agree to practice contraception and to use a highly effective method of contraception during the trial, including the last follow-up visit (12 weeks after ceasing drug).

⁃ Able to provide written informed consent.