Vaping products are the most commonly used method, which is a pharmaceutical grade precision engineered controlled dose of cannabis heated  into a mist or a vapor. But there are other options such as sublingual tinctures and hard pressed tablets. Each has its postives and negatives. 

There are a multitude of reasons that patients may accidentally overdose and become too high, but no one has ever overdosed.

Side effects can include changes in mood, lack of coordination, trouble thinking, increased appetite, diffculty conctrating, urninary retention, slurred speech, dizziness, red eyes, dry mouth, slow reaction time and lethargy.