What do you suggest if my friend has a condition called 'addison's disease' which is a fault with his adrenal glands. if i'm a match, would it be possible to donate?

No : Hi. Addison's disease is not ever treated with organ transplant. It is very easily treated with medication and education about how to manage severe illness/stress. It's kind of you to think of donating an organ to help, but you get to keep your adrenals! You CAN, however, be listed as an organ donor on your driver's license in case you're killed. That's a nice thing to do for someone.