With opiate wd, one dead ringer, pupils really big, it is one of the first symptoms of wd, even before the other nasty stuff starts and they stay that way a few days for most people. He will be extremely sensitive to the light.
But, there is another thing, if he is working outside in the heat the same symptoms as wd would be heat stroke, cramping, throwing up, general malaise, you won't be immune to heat stroke just case you are high, my husband had heat stroke many a time in active heroin addiction ...
Also I would remove the addiction as was suggested, really he is mean and the drug use isn't a good enough excuse for that at all, and should be never be an excuse. You do not have to take the abuse.