Hello Friend, Good that you are seeking a help. Solution for such problems is to make him understand that such thoughts are unnecessary. Instead of trying to control it, First accept it and then learn to ignore through few self therapies. Medicine will only suppress those thoughts temporarily.
What he wants?.
Better consult him with a psychologists to assess his deep rooted thoughts which can trigger such negative desires.
Next Steps
Consult a psychologists directly or online. Feel free to reach out to me online through Practo app for further evaluation and recommendation.