Dry eye disease (DED) is a multifactorial disease of the ocular surface characterized by loss of homeostasis of the tear film and accompanied by symptoms such as ocular discomfort and visual disturbance. DED is one of the most common reasons for seeking medical care in the United States and across the world. Despite this, there are a limited number of pharmacologic therapies for the treatment of DED in the United States and Europe. This review examines the different pivotal trials for DED medications and the impact the vehicle in each trial. In recent clinical trials, the vehicle of the active formulation of the medication is often used as the active comparator. A literature review of published dry eye clinical trials was performed to identify the pivotal clinical trials of DED medications and to compare treatment effect and further understand the impact of the vehicle on clinical trial outcomes. The pivotal clinical trials for the currently approved treatments for dry eye have widely varying study designs. The variations include differences in inclusion criteria, outcome measures and efficacy endpoints, and whether or not the use of concomitant artificial tears is allowed. These differences make it difficult for accurate comparisons to be made between DED medications. Each trial demonstrated that the vehicle alone has some beneficial effect on signs and symptoms of dry eye disease. This review discusses the varying trial designs and vehicles used in the pivotal studies for the four approved dry eye medications in the United States and Europe, as well as novel vehicles under development and clinical trial recommendations.