"i&#039;m 27 and i just started taking doxycycline 2x a day 100mg. i saw my skin clearing up or at least no new pimples since day 1! i also use tretinoin cream at night and benzaclin/clindamycin in the morning. i had an upset stomach so far only for one day but the past two days i&#039;ve been dealing with a bad headache. i&#039;m hoping it&#039;ll go away soon. other than that, this medicine works great on me!"