The correct way to do it is to click on the item (so that the cursor changes it to it), then right-click on a character's portrait. By the way, the aloe leaf cures a bit of health, but only the ginseng plant can cure poison – that's the item depicted as a green plant with a stem and some leaves.

don't forget to sleep it off when you're hurt, it's the cheapest way to heal up

Thanks for that Charon .. it really helped :)

Thanks also Cat .. but resting mostly doesn't cure poison & it was the poison that was causing me problems

If I remember correctly they don't actually die, they just fall unconscious. If one character gets poisoned let the poison bring him down and then cast a healing on him. He should be back in business. Of course that doesn't work if the whole party is being poisoned. When the whole party is unconscious the game is over.