Author William Fiennes has lived with Crohn's disease since he was a teenager. Despite debilitating symptoms, he has written two bestselling books and co-founded the charity First Story, which promotes writing in secondary schools. He reflects on his experience of the disease and how it affects him now.

"I first knew something was wrong when I was 18 years old. I was having a year out in Brazil working as a teacher, and started getting unexplained abdominal pain and persistent diarrhoea.

"I was reluctant to talk about it or seek help, so I didn't see a GP until about six months later, when I was back in England. It was then that I was diagnosed with Crohn's disease. The treatment options around that time were quite limited. There were no biologics and I was put straight on steroid medication.

"Being on steroid medication during my time at university wasn't easy. The side effects were unpredictable and really affected my emotions. Sometimes they gave me a boost and I was full of energy, and sometimes I felt very low. Also, although steroids can be incredibly effective and helpful, they only keep you in remission for so long. As soon as I came off them, the symptoms would return.

"I started pretty much every other kind of treatment that was available, including complementary medicines, and tried changing my diet, but nothing really got to the symptoms.

"This cycle of flare-ups and remission continued for the next few years until, at the age of 24, I was offered the option of surgery. I had a loop ileostomy, where the surgeon diverts your bowel to a stoma to give your colon (the part of my bowel affected by Crohn's) a chance to rest.

"I lived with a bag for 18 months. It was not an easy time. After that, they reversed the surgery and my colon was reconnected.

"I felt pretty good for the following year, before my symptoms returned."

Living with the condition now

"At the moment, I feel pretty stable. I'm currently taking a mixture of infliximab (one of the biologics) and an immunosuppressant called 6-MP (mercaptopurine). This combination therapy is effective and the big advantage for me is that I can avoid steroids. I've been taking 6-MP for the past year and am so glad I decided to go on it.

"If I'm in remission, I can eat pretty much anything, although there are certain foods that I avoid because they make me feel uncomfortable. If I'm having a relapse, everything is hypersensitive.

"Crohn's disease does interfere a lot with my work. It's very hard to write a book when you've got constant pain in your abdomen and you're running to the bathroom all the time.

"When I'm not writing, I'm teaching and helping to run First Story. I also like to run, swim and play cricket. But if I'm in a bad state, it's incredibly hard to do those things. It can be hard to muster up the strength, and I just want to flop and lie down.

"Crohn's disease grinds on and on. It zaps you of vigour and energy – both physically and psychologically.

Misunderstood

"Crohn's is a hard condition for people to understand. Everyone's familiar with diarrhoea, but normally for just 24 hours. What they've got to imagine is diarrhoea for 24 hours every day for months, with pain and weakness.

"Also, people make the assumption (as Crohn's is a bowel condition) that it's to do with food allergy and you can just cut out certain foods like dairy or wheat and that will solve everything. While this might be helpful in some patients to an extent, it's not in any way a treatment for such an organic disease.

"I'm not sure why I developed Crohn's disease. I've never been a smoker and no-one in my family has it. It's possible that I had a genetic predisposition and the disease was triggered by the bacteria and viruses I was constantly exposed to in Brazil, where I first started getting symptoms."