My dermatologist recommended tranexamic acid orally for melasma

I have had patients who have had some success with oral tranexamic acid for melasma. However, I have had much greater success for treating melasma with Cosmelan. Cosmelan is the best treatment to reduce and eliminate melasma. Through the use of hydroquinone and retain-a the pigmentation will be resolved.  Careful sun exposure is necessary to stop the recurrence of your melasma.  Best, Dr. Green

T. acid can help with the vascular component of melasma, another option is Cosmelan - Dermamelan peel. Dr Michelle Green in NYC is an expert. 
Melasma can not be completely cured, however effective treatment are possible. Melasma patients have skin that is very sensitive to UV light. Even the smallest amount can stimulate your pigment cells to produce colour. The mainstay of treatment is strict UV protection- hats, sunglasses and SPF every 4 hours. 
I prefer to use a combination of creams and laser for melasma. My most frequently prescribed topicals include hydroquinone, along with vitamin A creams and botanical extracts. The exact percentages will depend on your skin sensitivity, clinical presentation and your current skin care routine. 
I usually start my patients on a series of lasers (low dose Q switch or Picosure), along with medical therapy. Another laser I use is the Clear and Brilliant in the Permea setting. In some cases I combine glycolic AHAs, TCA low strength single coat peels, and in other cases I use a tablet called Tranexamic acid to help modulate the blood vessels that are associated with melanocytes (pigment cells). Melasma treatments should be tailored to each patient. 
All the best, Dr Davin Lim. Laser, surgical and aesthetic dermatologist. Brisbane, Australia. Cutis International