Hi, Welcome and thanks for posting your query to HCM. Lymecycline is a tetracycline base broad-spectrum antibiotic, the standard dose of 408 mg is equivalent to 300 mg tetracycline base and in its action to 500 mg tetracycline hydrochloride. Your doctor has prescribed as a part of treatment of acne. The known side effects include rash, headache, gastrointestinal problems, dermatitis, and visual disturbances. There is no direct evidence of the drug causing melasma. Melasma is one of of the pigmentation condition of face which is exacerbated by sun exposure and as all the tetracycline are known to cause photo-sensitivity and photo-toxicity( more or less), so it might be possible that this can aggravate the situation. As you are quite concerned about melasma than for acne so it is better to ask your doctor to shift you to those antibiotics which are not causing aggravation of melasma directly or indirectly- one good option is azithromycin which giving good response in acne and is quite safe in melasma also. One important advice is to reduce your stress level as stress can cause lot of problems including darkening of pigmentation in melasma too!! Hope this information prove to be help for you, Dr Sanjay K Kanodia