What are the physiological effects of drinking heavy water (deuterium oxide)?Heavy water is not radioactive. The deuterium in it is stable; it does not decay. You'd be in no danger at all from radiation.
Heavy water, being (literally) heavier than plain water, performs a bit differently in chemical reactions, but only a little, so you'd have to drink a LOT of heavy water for it to kill you. Experiments say you'd have to replace about 25% of the water in your body before you'd notice the effects, which would take about a week of drinking nothing else. At $600 a liter from United Nuclear, a week's supply would cost on the order of $10,000.
There is another form of heavy water, made with tritium rather than deuterium. It's somewhat radioactive, perhaps dangerously so if you drank nothing else. But tritiated water is much, much more expensive than deuterated water. It's treated as a radiation hazard, so it's much harder to come by. (Unless you happen to be drinking directly from Fukushima, where the tritium is a tiny fraction of the overall water content, albeit enough that you wouldn't want to drink it straight.)