Hi Megan,
I know taking a drug like this can be a little scary, but keep in mind that the drug companies tend to go overboard on stressing side effects to appease the regulators and the lawyers. That said, some people do react adversely, but your doctor will monitor your blood to see if anything potentially harmful is going on. I got my bloods done every two weeks at first, then down to once a month, then 6 weeks, then 8. As long as you keep up with the blood work and keep in touch with your doc, you should be fine.
Several bits of advice I have learned from taking Imuran:
1. Your dosage usually depends on you weight, so the more you weigh, the more you can tolerate. I am around 125 lbs and was not able to take the 150mg dosage due to severe nausea, so I went back down to 100mg.
2. According to my doc, it's best to start off on a low dose and ramp it up. He used the analogy of turning on a hot faucet...it takes a little while to adjust before you can turn it up to the max. Judging from comments on the forum, I don't think every doctor prescribes it this way, so you might want to talk to your doc about it.
3. It's best taken with food. Also, if it makes you nauseous, ask your doctor about splitting your dosage. Some people on here do it that way.
Other than nausea when on a high dose, I never have had any problems with Imuran. There are lots of threads on here with lots of info, so search around!
Good luck and keep us posted.