Leah Calvert Custody Battle: 'Teen Mom 2' Star's Ex Is Concerned About Her Drug Use [VIDEO]

Leah Calvert and Corey Simms' custody battle is heating up.

'Teen Mom 2' Star Leah Calvert "Shocked" After Corey Simms Files For Full Custody Of Twins

According to a new report, Simms fears Calvert isn't properly caring for their twins, Ali specifically, and has grown concerned about her use of prescription drugs. As a result, the reality pair are heading to court in Kanawha County, W.V.

“Corey has made it clear that will stop at nothing to win this case,” mainly because of his ex-wife's "drug issues," which he believes could affect the safety of their four-year-old twins, a source revealed to In Touch Weekly.

Corey Simms On Leah Calvert's Parenting: They "Just Need Structure"

During the fifth season of Teen Mom 2, Calvert was seen telling her current husband, Jeremy Calvert, she felt "druggy" after taking a pill for anxiety. Although Calvert was prescribed the medication by a doctor, her body didn't respond well to it, and she was later seen slurring her words while on the phone with Ali's doctor.

In addition, Simms is "deeply disturbed" that Calvert has been failing to take their daughter, Ali, to her physical therapy appointments. Because Ali suffers from muscular dystrophy, she needs to stay active and strengthen her muscles.

“Corey believes he’s in a position to provide more stability and consistency than the children are receiving now,” Simms’ attorney Rusty Webb told the magazine.

Miranda Patterson is currently a stay-at-home wife, and will reportedly be more than able to assist Simms with the twins whenever needed.

Calvert and Simms are scheduled to return to court on Dec. 2.