Are medicines really safe to take? My grandma never took any till 90 when forced to.

Mostly, yes. All medicines are two-edged swords; they have benefits and risks. You take them when the benefit outweighs the risk. Your grandma was very lucky to survive until 90 without any medicines; but medicines have been around for thousands of years, and it is the very rare individual who makes it to old age without having to take at least a few of them.