When you have marines and marauders, and they have been trained for stim packs, and they enter a battle, and you are microing them around, and you want to use stim packs, are they already always in stim mode, or do you have to click the stim pack icon in the box (at bottom right of the screen) when you have marines selected on your screen?
Stim mode must be activated. Once activated it immediately takes 10hp of a Marine and 25(maybe 20)hp of a Marauder, while it also increase their movement and attack speed which only lasts 5 to 10 seconds(I'm not sure about the how long it lasts, but I can quickly look it up for you). If you want to continue to use Marines and Marauders late into the game then you might want to bring along Medivacs which would heal the damage caused by using stim. You can activate it more than once at the same time but the none of the effects stacks except for the health loss.(At least this was true in SC1 not sure about SC2)
[ot] This is a completely honest question in case you are not a troll: did coming here, registering, and creating a thread take less effort than... you know, clicking the icon in-game and checking if it does anything? Don't get me wrong, I'm all for asking help on a forum and such, it's just that this particular case is very weird. [/ot] One thing I'd like to add to the above is that your opponent can very well use fast units to attack you and then back off once you stimmed (and effectively damaged) all your infantry, so although it's tempting to use stim just before the battle to get the bonus right from the beginning, it's also risky in case the battle doesn't actually start.
Training for the combat shield from the Marauder tech lab does add 10 hp, thereby offsetting the hp loss from stimming, but I think having medivacs around would be a good idea. Now that I think about it, I've entered MANY battles without even thinking of bring medivacs along.
im surprised that you haven't tried clicking on the icon and not noticing a difference in the first place :/ stim pack is very powerful, you can hit and run and kill many units , you can chase down units, or simply plow through an army if you have medivacs. the only thing that can stop MMM (marine, marauder, medivacs) with stimpack in a even army match is aoe damage (colosus, high templar storm, inferstors, ultralisk, tanks) or sentry force fields to split the army and guardian shield.