Four friends are on track to raise more than £18,000 for young people's charity Holt Youth Project, after trekking through the wilds of Madagascar to climb a 9,000ft mountain.

Alison Mawson, 57, who is known as Dr Brooks to her patients at Holt Medical Practice, came up with the idea of completing the challenge after meeting Holt Youth Project staff and young people in the course of her work.

She recruited friends Diana Jacob, 55, Karen Siddall, 53 and fellow GP Catherine Scott, 54, – who is known as Dr Ashworth at Mundesley Medical Centre – and, after paying their own travel expenses, the intrepid quartet got together to come up with fundraising ideas.

A rainforest-themed ball and auction they hosted at the Auden Theatre, Holt, in January set them on the right track, bringing in £14,000 in ticket sales, auction bids and donations.

The four friends also set up a Just Giving online charity page which, with other donations, has taken their total so far up to £16,000.

'As a GP, I have seen the amazing work that Holt Youth Project does with young people with low self-esteem, mental health issues and low aspirations,' Dr Brooks said. 'I think that although Holt is an apparently affluent area, people don't realise how much deprivation there is and we felt it was really important to support a local charity.'

Previous charity challenges undertaken by the pals have seen them trek to Machu Pichu, Peru, raising £20,000 for Macmillan Cancer Support, go on an expedition to the Himalayas – again raising £20,000 for Macmillan - and, in 2012, travel to the Great Wall of China to raise £24,000 for Holt Youth Project and the research charity Against Breast Cancer.

They flew to Madagascar on Saturday, to spend nine days camping under the stars and trekking through canyons, gorges, dense forest and rocky plains to climb 2658m Pic Boby, which is nearly twice the height of Ben Nevis.

Proceeds from their latest challenge will go towards Holt Youth Project's Achieving Confidence Training (ACT) programme, which offers individually-tailored educational, vocational and social skills courses to young people with problems ranging from emotional and mental health issues, to autistic spectrum disorders.

To support Dr Brooks and friends' Madagascar challenge, visit www.justgiving.com/fundraising/Diana-Jacob1