It's not ambiguous at all - medications are allowed, including medically necessary liquids.

Explosives are prohibited.

Medical nitro (in all of its forms) is not an explosive.

However, some moron in a TSA costume prohibited Chollie from taking his nitro through because he was under the idiotic delusion that nitro medications are explosives. This is not true, has never been true, and is an urban myth on the level of the guy who woke up in a bath tub of ice with a kidney missing. Yet the TSO not only forced him to dispose of his life-saving medication before transiting the c/p, the moron was also backed up by his moron supervisor when Chollie protested.

This is the level of intelligence evident in the average TSO - they actually think that medical nitro is an explosive. They probably think that the nitro explodes in the body to get the heart started after a heart attack (it's actually a vasodilator which opens blood vessels to improve blood flow). And although it's stated on the TSA blog somewhere that medical nitro is permitted, Chollie has been so spooked by the experience that he has never again tried to carry his nitro with him.