There is always a risk with any medication taken during pregnancy. However, medications most often prescribed typically present less risk to the mother and child than chronic dehydration and lack of nutrition. The risk decreases after the first trimester or around 10 weeks, but if vomiting is left uncontrolled until then, the stress on the body is great and it is much more difficult to stop the vomiting. These women are then at greater risk for complications and a prolonged recovery. They often will have great difficulty caring for themselves and their family for months. Medications are often more effective if started early because there are fewer nutritional deficiencies and the mother is in better overall health. It can be compared to pain control: most health professionals know that when pain medicine is given early for pain, rather than later, the pain is easier to control. The same holds true with vomiting. The consequences and complications are typically less if the nausea and vomiting are controlled earlier rather than later.
More Info on Medication Safety: http://www.helpher.org/family/treatment ... ations.php