Objectives: The aim of this study is to determine how to fully describe the drug as an intervention registered in the Intervention section of the ClinicalTrials.gov Registry in clinical interaction studies involving interventional designs and which has only one or two different drugs in the Register mentioned as an intervention. Methods: An advanced search engine for the ClinicalTrials.gov (in the scope of a major study part of this pilot study) has included a key term for drug-drug interaction (s), and all clinical trials that have 1) had a registration NCT number, 2 ) were registered on October 16, 2015 or earlier, and 3) were marked as closed and completed. Two researchers (AB and DJ) carried out an independent random sample extraction for a random sample of 10% of the conducted trials, and a final extraction protocol was then determined. Information for 12 items from TIDieR Checklist was collected. The data were processed in Excel, and a descriptive analysis were performed with the MedCalc statistical version, version 17.9.4 (MedCalc Software, Ostend, Belgium). Results: Most of the interventions did not have a good description of the pharmacological intervention and listed all the required information in accordance with recommendations from the TIDieR checklist. The generic name of the drug was registered in 77,0% cases, and trade name for 25,6% of interventions. 21,9% of the cases included just the special code. Contrary to recommendations most interventions did not have the indicated pharmaceutical form and almost one third of them did not have information about dose, duration of use, or route of administration. The manufacturer is listed in only 1,2% of cases. More than half of the clinical trials did not have a theoretical explanation or the hypothesis mentioned above, but only the pharmacokinetic or pharmacodynamic specificity test or the safety of the application. Most of the studies also had no mention of the delivery of the pharmacological intervention to the patients (72,2%), nor the person responsible for the intervention (99,5%).Conclusions: There should be more stringent requirements when registering clinical studies of pharmacological interventions in the ClinicalTrials.gov register. Potential solutions include: better regulatory requirements, extension of the current guidelines for clinical trials of pharmacological interventions, stricter and more extensive requirements for all components included in the description of pharmacological intervention in the Descriptive Information Registry ClinicalTrials.gov section.