Intravenous magnesium sulfate tocolysis remains a North American anomaly. This therapy rose to prominence based on poor science and the recommendations of authorities. However, a Cochrane systematic review concluded that magnesium sulfate is ineffective as a tocolytic. The review found no benefit in preventing preterm or very preterm birth. Moreover, the risk of total pediatric mortality was significantly higher for infants exposed to magnesium sulfate (relative risk 2.8; 95% confidence interval 1.2-6.6). Given its lack of benefit, possible harms, and expense, magnesium sulfate should not be used for tocolysis. Any further use of magnesium sulfate for tocolysis should be restricted to formal clinical trials with approval by an institutional review board and signed informed consent for participants. Should tocolysis be desired, calcium channel blockers, such as nifedipine, seem preferable.