Neath, Morriston and Singleton hospitals are the first to trial aloe vera as a treatment for irritable bowel syndrome (IBS), which affects around 20% of the UK population.
More than 250 IBS sufferers in the region are taking part in the two-year study, which will cost £50,000.
One of the volunteers Glyn Stevens, from Swansea, said the condition, which ranges from acute diarrhoea to constipation, has had a profound affect on his life.
"The pain is really bad and affects me on a daily basis," he said.
"It makes me cough so much it almost chokes me."
Sufferers often desperately need to go to the toilet with little warning, which severely limits their lifestyle.
Claire Hopkins, 26, from Penclawdd, said: "I have terrible stomach problems which have really affected my life.
"A cure would be marvellous."
So far clinical research has failed to identify the causes of IBS or a remedy for the condition.
However, experts working on the aloe vera trials are hopeful they can exploit the plant's healing properties.
Professor John Williams, consultant gastroenterologist, said: "IBS is very debilitating, causing troublesome symptoms which interfere with the social and working life of the individual.
"This is a study to look for an alternative treatment.
"There is a lot of anecdotal evidence of the beneficial properties of aloe vera but this has never been proven."
Alternative medicine
Aloe vera is not a drug but is derived from a plant which is part of the lily family.
It has been used as a complementary treatment since the 18th Century.
Each aloe vera plant takes about five years to mature and has a life span of about 12 years.
The leaves are harvested between three and four years of age which is used to make the liquid, which will be the basis of the research.
The study is being funded by the Foundation for Integrated Medicine.