Isopropyl alcohol (rubbing alcohol) and ethanol alcohol (liquor) are two very different things. Both chemicals are poison, but isol alc is literally a corrosive compound that illicits no euphoric...
ANY amount which impairs you is too much. For the "average" adult the body can synthesize approximately 1 ounce per hour. Any more than that amount at that rate, and the body is not able to throw off...