Where possible, medications should be avoided during pregnancy. Most medications will cross the placenta to the baby and certain agents may be teratogenic (toxic or cause structural abnormalities).
The absorption, excretion and metabolism of medication are changed due to the physiological changes of pregnancy. This affects types and dosages of medication.
If you are on medication for medical conditions, you may need to make adjustments. This does not necessarily mean that you need to stop taking medication. Stopping therapy in conditions such as epilepsy, hypertension, asthma or diabetes would be extremely dangerous. In such cases, your doctor will prescribe the safest medication which may differ from that used before the pregnancy.
Avoid over-the-counter medication and agents containing additional vitamin supplements, unless they have been approved by your doctor.