The medical term for difficulty with swallowing is "dysphagia" and more can be read about it here http://www.nhs.uk/conditions/Dysphagia/Pages/definition.aspx I believe in Dr Kelly's case it has been suggested that he didn't have any apparent difficulty in swallowing food, his dysphagia was confined to swallowing tablets. This sounds like a very unusual condition but I have had the odd occasion when I have found it extremely difficult to swallow a tablet, almost to the extent of giving up. Personally I'm not particularly keen on taking tablets but there are occasions when one just needs to do so.
If Dr Kelly did have an aversion to taking tablets the question to be asked is whether he just didn't like the idea of taking a medicine or was there a physical difficulty that stopped him so doing. This is part of a report by Sharon Churcher in the Mail on Sunday relating how Dr Kelly's confidante Mai Pederson was surprised to hear that he had taken an overdose of co-proxamol:
Ms Pederson’s Washington DC lawyer, Mark Zaid, has made available to The Mail on Sunday parts of her final statement to Thames Valley Police, given on September 1, 2003.
Its ten pages would appear critical, since they describe Iraqi death threats and the incident with the laser. She also stated that she was bewildered about how Dr Kelly could have taken an overdose, as he suffered from a disorder that made it difficult for him to swallow pills.
‘I was so confused when I heard he had swallowed a load of painkillers,’ she told the officers.