While taking minocycline, a person should avoid prolonged, unprotected sun exposure. As with other antibiotics, taking minocycline may disturb the balance of normal bacteria residing in the body. This may show up as bacterial overgrowth. An example of this is yeast infection occurring in women taking antibiotics. Taking antibiotics over a long period may make bacteria less susceptible to being killed by the antibiotic.
Tetracycline antibiotics make penicillin antibiotics less effective.
Therefore, if penicillin is needed, the minocycline should be temporarily discontinued. One of the more common side-effects in persons taking minocycline for a long period is a discoloration of the skin. The skin may develop a bluish-grey complexion. Bruises may be darker and take longer to go away. Some persons have described changes similar to a dirty suntan.