As HoH, you are responsible for taking care of your TIH’s health and wellbeing.

If your TIH has been prescribed medication, you need to ensure they take medicine as prescribed.
If your TIH is in pain, feeling unwell or has depression, you must ensure that they take their medication regularly.

If they are busy in the home and work lives, it is easy to forget to take regular medication.

As HOH take responsibility for seeing the medication is taken as prescribed.

Putting any medication in daily pill boxes is an easy way to monitor what has been taken.

If medication has not taken, you need to talk to your TiH and explain why it has to be taken as prescribed, and if they continue to miss taking medication, they will be held accountable.

At first, I would suggest punishments such as removing privileges like screen time,  or any activities that they enjoy doing.  If they persist, then you will have no option but to spank them.