Adverse events

Participants assigned to HCL group will initially be randomly assigned 1:1 to use either the Tandem t:slim X2 with Control-IQ technology or a Medtronic HCL system (Medtronic 670G 4.0 AHCL (prior to protocol version 5.0) or Medtronic 780G (starting with protocol version 5.0)). This group will receive intensive diabetes management with frequent contacts by study staff with the goal of near-normalization of glucose concentrations. Verapamil will be taken orally once per day by participants in Cohort A. A dosing scheme will be followed, using 120mg tablets or 60mg half tablets. Whether drug is active or placebo is blinded to both participant and site. \[Cohort B participants will not receive study drug. Instead, they will be randomized 2:1 to HCL or non-HCL.\] HCL: Hybrid Closed Loop therapy verapamil 120mg tablet: verapamil tablet

Participants assigned to HCL group will initially be randomly assigned 1:1 to use either the Tandem t:slim X2 with Control-IQ technology or a Medtronic HCL system (Medtronic 670G 4.0 AHCL (prior to protocol version 5.0) or Medtronic 780G (starting with protocol version 5.0)). This group will receive intensive diabetes management with frequent contacts by study staff with the goal of near-normalization of glucose concentrations. Placebo will be taken orally once per day by participants in Cohort A. A dosing scheme will be followed, using 120mg tablets or 60mg half tablets. Whether drug is active or placebo is blinded to both participant and site. \[Cohort B participants will not receive study drug. Instead, they will be randomized 2:1 to HCL or non-HCL.\] HCL: Hybrid Closed Loop therapy placebo: placebo pill manufactured to mimic verapamil 120mg tablet

Participants assigned to non-HCL will receive a Dexcom G6 CGM and diabetes management will follow usual care by their personal diabetes health care provider. Verapamil will be taken orally once per day by participants in Cohort A. A dosing scheme will be followed, using 120mg tablets or 60mg half tablets. Whether drug is active or placebo is blinded to both participant and site. \[Cohort B participants will not receive study drug. Instead, they will be randomized 2:1 to HCL or non-HCL.\] verapamil 120mg tablet: verapamil tablet non-HCL: Usual diabetes care

Participants assigned to non-HCL will receive a Dexcom G6 CGM and diabetes management will follow usual care by their personal diabetes health care provider. Placebo will be taken orally once per day by participants in Cohort A. A dosing scheme will be followed, using 120mg tablets or 60mg half tablets. Whether drug is active or placebo is blinded to both participant and site. \[Cohort B participants will not receive study drug. Instead, they will be randomized 2:1 to HCL or non-HCL.\] non-HCL: Usual diabetes care placebo: placebo pill manufactured to mimic verapamil 120mg tablet

Participants weighing \<30 kg at study enrollment were randomly assigned 2:1 in a parallel group design to HCL plus intensive diabetes care or usual care with no HCL. Participants assigned to HCL group will initially be randomly assigned 1:1 to use either the Tandem t:slim X2 with Control-IQ technology or a Medtronic HCL system (Medtronic 670G 4.0 AHCL (prior to protocol version 5.0) or Medtronic 780G (starting with protocol version 5.0)). This group will receive intensive diabetes management with frequent contacts by study staff with the goal of near-normalization of glucose concentrations. HCL: Hybrid Closed Loop Therapy

Participants weighing \<30 kg at study enrollment were randomly assigned 2:1 in a parallel group design to HCL plus intensive diabetes care or usual care with no HCL. Participants assigned to non-HCL will receive a Dexcom G6 CGM and diabetes management will follow usual care by their personal diabetes health care provider. non-HCL: Usual diabetes care