Active Active Thyroid Is It True That A Person With Hypothyroidism (under Active Thyroid) Cannot Lose Weight?

Is it true that a person with hypothyroidism (under active thyroid) cannot lose weight? - active active thyroid

I have a thyroid, and I lost 70 pounds. But I've heard that it would be impossible. Is this true or not? And if not - what can a man do in this situation in order to lose weight?

I take thyroid medication, on the street.
Thank you!