Introduction:Spinal anesthesia is one of the most popular methods of anesthesia for caesarean. One of the major side effects of this method is the headache that the patients would experience as a result of spinal anesthesia. Ondansetron and dexamethasone have been reported to be very useful in reducing these headaches. The present research seeks to study the effects of these two types of medicine in reducing the headaches caused by spinal anesthesia among women candidated for caesarean. Materials and Methods: This is a double-blind clinical trial conducted on 120 mothers candidated for elective, second time caesarean. They were divided into the following groups with 40 participants in each one: dexamethasone, ondansetron, and placebo. 8 milligram of IV dexamethasone was used for the first group, while the second group was given 8 milligram of IV ondansetron, and the third group was given the same amount of IV distilled water. After the operation, patients' pain scores were measured at 12, 24, and 48 hours following the operation and the average amount of painkiller used 24 hours after the operation was recorded. SPSS 19 was used to analyze the data. Results: A significant difference was observed between the three groups in terms of the frequency of post-spinal anesthesia headache. This frequency was significantly higher in placebo group compared to what was observed in the other two groups (P = 0.01). Conclusion: Finally, it turned out that both dexamethasone and ondansetron are very effective in reducing headaches caused by spinal anesthesia. Statistics show that dexamethasone is much better and more effective than ondansetron.