Hi, thanks for asking in Healthcare Magic. Adderall is a combination of Amphetamine and Dextroamphetamine. It is given in ADHD (attention deficit hyperactivity disorder). Metronidazole is given in Protozoal infections like Amebiasis and Giardiasis. Doxycycline is an antibiotic. Broadly speaking, except for the fact that Metronidazole can increase the level of co administered drug by inhibiting their breakdown in liver, no serious interaction will be seen among these three drugs. At therapeutic doses, Adderall can be combined safely with the other two, provided that Metronidazole and Doxycycline are given for a short period. However, when given together, there may be an overlap of common side effects among these drugs. Both Metronidazole and Adderall can result in metallic taste, nausea, diarrhea, anorexia (loss of appetite) and headache. When given for prolonged period, doxycycline can cause oral candidiasis (white tongue) which can be confused with the flurry tongue caused by Metronidazole. I hope this is useful to you.