Moon gives me final instructions and closes the door. I'm alone with jazzman Kenny G on the stereo, turned up just loud enough to disguise my yelp of surprise as I discover the lubricating olive oil and long tube ready for my 10-litre coffee colonic.

Koh Pha Ngan, in southern Thailand, is known as the party island, its Haad Rin beach infamous for hosting full-moon parties of up to 10,000 fluoro singlet-wearing, whisky bucket-drinking revellers in a debaucherous free-for-all on the sand. A few years ago I was part of that beach crowd, wearing fisherman's pants, twirling glow sticks and drinking into the wee hours. Returning to Koh Pha Ngan older and a little wiser, I'm seeking to explore the island's holistic side, so I bypass the parties and head over the island's spine to the Anantara Rasananda resort on the edge of Thong Nai Pan Noi village. The resort will be my base while I unwind and detox.

A yoga session at Anantara Rasananda resort.

The village has one crumbling road lined with cafes, laundries and a traditional Thai boxing ring. Chickens roam free and there isn't a go-go bar in sight or techno music to be heard. I sit on the beach by day and eat at the Bamboo cafe at night. After the third night, Peekan, the cafe owner and chef, offers to teach me how to cook chicken laab.

The tail of a cyclone that hit the Philippines is lashing this part of the Thai coast, preventing me taking a boat from Haad Rin to The Sanctuary, an eco-resort built on an isolated stretch of Koh Pha Ngan's Haad Tien Bay, so I hitch a ride with a farmer. The bay is a tropical paradise at its best: white coral sand, warm water and swaying palms.

The Sanctuary's manager, Mike Doyle, is waiting for me and demonstrates the barefoot, open-shirt attitude of the place as we chat over ginger-and-lemon tea with honey. Originally from Ireland, Doyle travelled via Australia to Koh Pha Ngan and was appointed manager in 1998.

The resort's spa in Koh Pha Ngan.

I see people playing soccer, practising yoga and reading with beers in hand. As Doyle describes it, The Sanctuary is full of all sorts: "Loan sharks, students, musicians and business executives."

I have fasted before arrival and will avoid consuming alcohol and meat on the day before my rapid-detox program begins. I'll get nutritional shakes, supplements and advice from the staff before the colonic. For my last meal before then, however, I order from an enzyme-rich menu: a confetti salad of carrot, daikon, cabbage, sweet potato and pumpkin, followed by a "hot and raw soup" of vegetables "introduced" to hot water before being blended with broth, garlic and ginger. While the benefits of a detox program are what draw many here, Doyle says that when people are deep into the process he'll often see them lingering near The Sanctuary's cake cabinet like desperate window shoppers.

I walk through the resort's tranquil grounds, take part in an afternoon yoga session and take a seat in the herbal steam room while waiting for my detox appointment. At the "health bar" I meet Belle, a dubstep singer from London who is four days into a seven-day detox. There are 19 other participants here and among them are drinkers, smokers, gallstone sufferers and those looking to lose weight and gain a tan. Belle sips coconut water and, although she looks a little drained, tells me she has more vitality than she can remember. "I wake at 6am full of energy and do two hours of yoga," she says. "I'm used to getting home at that time." She is undertaking an extended version of what I'm to attempt: four psyllium-husk shakes with bentonite clay each day, no solids and an afternoon colonic. As odd as it is for strangers to chat about bowel movements, Belle says she is considering taking on the 10-day cleanse because she feels so good.

Soon enough, it's my turn. Moon, the resort's "wellness expert", pushes a purple psyllium-and- clay shake in my direction and suggests I drink it quickly. "It will expand like porridge once it's inside," he says. Psyllium husks are a hygroscopic source of fibre and bentonite clay is used as a laxative that absorbs toxins. I skol the shake.

Detox patients have their own bathrooms, equipped with a shower, incense, music and a colema board. The colonic solution is two cups of organic coffee, three tablespoons of apple cider vinegar and 10 litres of warm water in a gravity-fed device. I hear a few of Moon's words before he closes the door and departs: "Recline"; "lubricate"; "10 litres"; "relax".

I sit and contemplate Haad Rin - hedonism central on the sand; paying for those sins here - and remember the junk food and alcohol I've consumed in the past year. I think of what Doyle said about The Sanctuary when I arrived: "It's where you take responsibility for yourself and your actions." Then I disrobe and assume the position. With the music turned up, I take responsibility in hand and recline.

Ben Stubbs travelled courtesy of Thai Airways and the Anantara Rasananda.

FAST FACTS

Getting there

Thai Airways has a fare to Koh Samui from Sydney and Melbourne for about $1190 low-season return, including tax. Fly to Bangkok (about 9hr), then to Koh Samui (1hr 15min); see www.thaiairways.com. Ferries run daily services from Koh Samui's pier to Koh Pha Ngan. Tickets from 500 baht ($16) a person return. Speedboat transfers are also available.

Detoxing there

The Sanctuary, Haad Tien Bay, can be reached direct from Koh Samui by the same ferry service, by longtail boat from Haad Rin beach and by road taxi from Anantara. A one-day detox costs from 2750 baht and includes pre-detox interview, all supplements and shakes, meditation and steam room access; see thesanctuarythailand.com.