I already described you it above... But give me time to afternoon, I'll play game again especially to help you.

EDIT (again):
Ok, got it.
My mistake, sorry, but now it's full correct:
If you have got low health and use one time number of medcines enough to restore full health this Achievment is unlocked.
So it means:
Perfect Patient - make one portion of pills that make your health full.

And now everything is correct

I try but I can't. One recipe, please

I am not able cause it depends WHEN you use pills. Health of Ellen is going down slowly but in real time. In inventory You have list how much HP will be given by mixed pills so if you need 6 HP, use white-red and blue and You get full HP back.

Pic below as proof of my wisdom