Since the threat to food has become a key aspect of this discussion and has been posed an understandable rationale for the Captain's
unusual action, the following may be useful since eye drops are considered to be a likely source of food contamination. (Yes, Rainboe it was an unusual action because no other Captain has come forward to say he/she ever had to undertake this type of diversion (cost estimate roughly $10,000) to deal with an unruly crew member. In fact several have said they haven't ever heard of a fellow Captain doing so.)
While the side effects of ingesting eye drops may be dire, one of them is not a bout of diarrhea.... according to the myth busting site |Snopes.com
However. Drinking or otherwise taking eye drops (active ingredient tetrahydrozoline) internally can lead to blurred vision, low body temperature, an elevated then sharply dropped blood pressure, nausea and vomiting. If enough has been ingested, the person can experience seizures, tremors or even slip into a coma. Anyone who would even consider doing this to someone else, especially someone entrusted with their safety, is an absolute idiot.
Those who have supposedly suffered the runs from eyedrops and see this as confirmation of food tampering as a regular occurance may have to consider another cause.