I am glad that you are a good enough friend to ask of this concern. As with any prescription medications, the results would vary especially when stopping the medication abruptly without the physician who prescribed the medication being aware.
I would say your friend who has decided for one reason or another to stop taking the medication, depending what it is being prescribed for is in danger.
You can not force your friend to take the medication, and remeber you are not responsible for your friends choice.
For me when I decided to try to stop taking the Risperdal prescribed to me for Bi polar disorder, I became very anxious and ultimatly very depressed. Luckily I was still within the frame of mind to beging taking it again. It took a couple of days but I got back to 'myself'
I would encourage you to keep an eye on your friend for signs of mental decompensation or 'problems' and let someone close to your friend who is involved in his/her treatment (parents or such) know that they have made this decision. _ best wishes- Chris
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~KRIS~
If you think you have totally gave up, you haven't, because you are here!