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Gynaecomastia or male enlargement of breast is usually caused by hormonal changes occuring during puberty,drug effect,illegal drug use,any outgrowth etc.
Obesity can also cause them to look enlarged in size.Usually after few years in many cases it resolves by itself.
But if there is any underlying cause which needs to be treated then it would require appropriate treatment as medicines or surgery.If there is any tenderness then it would require medications.It requires a proper examination of the area to comment regarding this.
Kindly visit a Physician for evaluation so that he can guide you further.
Take care!