Hi, There is no documented any harmful interactions between these two medicines hence they may be taken together. Based on the history your son seems to be suffering from a skin infection not responding to Bactrim and hence the doctor prescribed Clindamycin. Clindamycin is commonly prescribed to treat skin infections caused by susceptible bacteria. Its common side effects include nausea, vomiting, abdominal pain and diarrhea which can be troublesome in some patients. The common side effects of Adderall include lack of sleep, headache, anxiety, agitation, dry mouth, increased heartbeats, palpitations, loss of appetite, and constipation. Kindly inform his doctor if he experiences side effects which are troublesome. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Mohammed Taher Ali, General & Family Physician