"When a criminal defendant enters a guilty plea, the trial court is required to ensure that the plea is knowing and voluntary." (People v. Cross (2015) 61 Cal.4th 164, 170.) The trial court should "cause an inquiry to be made of the defendant to satisfy itself that the plea is freely and voluntarily made . . . ." (Pen. Code, 1192.5; People v. Palmer (2013) 58 Cal.4th 110, 112.) "The purpose of the 'knowing and voluntary' inquiry . . . is to determine whether the defendant actually does understand the significance and consequences of a particular decision and whether the decision is uncoerced." (Godinez v. Moran (1993) 509 U.S. 389, 401, fn. 12.) A defendant seeking to withdraw a guilty plea must show there were circumstances overcoming his or her exercise of free judgment. (People v. Ravaux (2006) 142 Cal.App.4th 914, 917; Pen. Code, 1018.) A defendant's ingestion of drugs does not alone show a plea is involuntary; rather, "there must be some evidence that the medication has affected his rationality." (Carey v. United States (1st Cir. 1995) 50 F.3d 1097, 1099; Oliver v. State (Utah 2006) 147 P.3d 410, 412.) When evaluating the voluntariness of a plea, a trial court is not required in every case to inquire about drug or alcohol use. (Carey, supra, 50 F.3d at p. 1099 court not required to make inquiry regarding drug use where there was no suggestion "defendant was not in complete command of his faculties".) However, when a trial court is informed the defendant has recently ingested a substance capable of impairing the ability to make knowing and voluntary decisions, the trial court should question the defendant "'with a view to assessing the impact of the ingested substances on the defendant's capacity to understand the change-of-plea process and intelligently determine a proper course of action.'" (Ibid.) Deficiencies in the trial court's inquiries at the time the plea was entered do not mandate plea withdrawal if the record affirmatively shows a knowing and voluntary plea. (See People v. Cross, supra, 61 Cal.4th at pp. 171, 179.) A trial court may properly decline a plea withdrawal motion based on a claim of drug ingestion if the evidence shows the defendant "was not impaired to the point that his independent judgment was overcome at the time he entered the guilty plea." (People v. Ravaux, supra, 142 Cal.App.4th at p. 918.) On the other hand, a defendant is entitled to withdraw his plea if "'he proved that his mental faculties were so impaired by drugs when he pleaded that he was incapable of full understanding and appreciation of the charges against him, of comprehending his constitutional rights and of realizing the consequences of his plea.'" (Oliver v. State, supra, 147 P.3d at p. 413.) On appeal from the denial of a plea withdrawal motion, we defer to the trial court's credibility resolutions and factual findings if supported by substantial evidence. (People v. Fairbank (1997) 16 Cal.4th 1223, 1254; People v. Ravaux, supra, 142 Cal.App.4th at pp. 917-918.) The relevant inquiry is "whether the defendant's guilty plea was intelligent and voluntary in light of the totality of the circumstances." (People v. Mosby (2004) 33 Cal.4th 353, 361.)