Works fast 2-3 days for visible improvements Not sure about long term acne use Some side effects mainly upset stomach I haven't been put on Amoxicillin for acne but within 3 days of taking the antibiotic my skin has started to clear up massively, on my face my back & chest with no new spots breaking out and the old ones are fading and having time to heal without still being infected. Can't believe it has worked so fast! I've been on amoxicillin in the past for tooth infections and also saw beneficial effects on my acne. It really works for acne but I'm not sure if a Dr or derm will prescribe this antibiotic for long term use for acne even though it really does work. The only side effect I've seen has been an upset stomach so I've started taking a probiotic supplement.