It's difficult to tell how advance your friend's diabetes is without knowing if that 170 was a fasting blood glucose or a non-fasting bg. If fasting, then it's high enough that he needs to get it down immediately, and his doctor was absolutely right to start him on medications. If his blood sugar is 170 fasting, then it's probably going way over 250 after eating.
As fishdude pointed out, ALL medications have side effects. Doctors usually weigh the risks of the medication versus the benefits of taking it. In your friend's case, the risks of NOT medicating are that he could develop all sorts of complications from uncontrolled diabetes...nerve damage (both peripheral and autonomic), eye problems such as retinopathy, kidney damage, vascular problems, and more. For some people, it doesn't take very long to develop side effects; thus his doctor has assessed that the risks of NOT taking medication are greater than the risks of taking it.
Your friend might possibly be able to get off medications down the road if he loses the excess weight and continues to monitor his eating, along with getting regular exercise. But the greater goal should be to keep blood sugar levels down by whatever means necessary.
Ruth