"i have been on doxycycline for at least 10 years straight for acne. i saw a big improvement in my skin when i first started taking the drug in my thirties. now that i&#039;m 48 and entering menopause, it seems to be a little less effective because of my hormonal changes probably. but i have never had any side effects with this drug, which is great considering the amount of time i have been using it."