Hello. Thanks for writing to us at healthcaremagic Let me answer your second question first. Doxycycline though as such won t cause any problem in conceiveing a pregnancy but it belongs to a tetracycline group of antibiotics, which may cause a permanent yellowish-grey-brown discoloration of teeth in neonates, specially if given in the second half of pregnancy.Therefore, the use of doxycycline during pregnancy is generally not recommended, especially during the last half of pregnancy. Doxycycline is rapidly effective in inflammatory acne and most people do notice a significant improvement in about 2-3 weeks,. The drug can be given for 8-12 weeks at a stretch depending on severity of acne. Topical treatment is an essential part in the overall management of acne, specially topical benzoyl peroxide gel as it is not only antibacterial and antiinflammatory but also prevents the development of bacterial resistance to doxycycline. Regards