Yes, several people do recommend that it's better to give up peanuts if you have a thyroid problem. This is because peanuts have a substance called goitrogens. Goitrogens can interfere with the working of your thyroid and thus aggravate your problem. Research has shown that when you cook food that contains goitrogens, the compound gets inactivated. Therefore roasted peanuts or peanut butter may lose some of these compounds. However, it's still fuzzy about what percentage of goitrogens is actually inactivated. It is therefore advisable for people with thyroid problems to avoid peanuts because it's not clear how inactive the goitrogens actually are.