Brief Answer:
try lifestyle changes first

Detailed Answer:
Hello,

Thanks for writing to us. I can understand your concern. As such weight gain with topamax is rare condition rather it causes reduce appetite and weight loss.
I first recommend going for some necessary blood investigations for weight gain like lipid profile, thyroid and routine blood investigations.

I want to clarify about Qsymia.

Qsymian is a combination of phentermine and topiramate. Phentermine is an appetite suppressant and belongs to a class of drugs called sympathomimetic amines. It is not known how this medication helps people to lose weight. It may work by decreasing your appetite, by increasing the amount of energy used by your body, or by affecting certain parts of the brain.
Qsymia is used with a doctor-approved exercise, behavior change, and reduced-calorie diet program to help you lose weight. It is used by certain overweight people, such as those who are obese or have weight-related medical problems.

Considering these facts I recommend lifestyle changes like exercise and diet management to reduce weight first. If you cannot succeed you can go for qsymia under your treating doctor's guidance.

Other option is you can shift to other medicine for migraine like propranolol , amitryptiline or valproate sodium.

Hope I have answered your query, I will be happy to help further.
Regards,
Dr.Chintan Solanki.

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