I am looking for people who have had a UN-TREATED underactive thyroid, and who have taken doctor prescribed Phentermine. my question is, have you lost weight while taking them? I started Phentermine one week ago, and I was just advised by my doctor that I have a underactive thyroid and I will need. AlaskaONE is the original internet based Alaska travel guide. AlaskaONE lists 100's of independent Alaska businesses of all sizes. AlaskaONE is your resource to learn about Alaska's diverse Parks & Places. It took care of the thyroid problem but I too am having weight problems (10-12 extra pounds I can't shed). I have been put on phentermine, recently. I used it years ago after having some kids. I lost the weight easily and kept it off. I used a much lower dose, though. I usually cut my 37.5 dose into quarters or smaller. I was able to sleep better at night and had fewer heart issues. If you. Losing weight is hard, but combining that with thyroid problems makes it even harder! Find out everything you need to know about your thyroid and phentermine! What Are Thyroid Problems? Through the hormones it produces, the thyroid gland influences almost all of the metabolic processes in your body. Thyroid disorders can range from a small, harmless. This is a thyroid forum and that's not really a question for our forum. I can tell you that phentermine is not meant to be a long term medication and there should be breaks in taking it. You should not use phentermine if you have glaucoma, overactive thyroid, severe heart problems, uncontrolled high blood pressure, advanced coronary artery disease, extreme agitation, or a history of drug abuse. Phentermine is not recommended for patients with symptomatic heart disease including rhythm problems. SIDE EFFECTS: Side effects include diarrhea, dry mouth, constipation, an unpleasant taste, hives, impotence, palpitations, high blood pressure, and fast heart rates. Central nervous system side effects include overstimulation, insomnia, restlessness, tremor, and dizziness. Doctors give trusted answers on uses, effects, side-effects, and cautions: Dr. Lin on phentermine thyroid test: Address your thyroid problem. Phentermine is a medication that is usedfor weight loss and to treat obesity. It acts as an appetite suppressant and should be coupled with exercise and diet in order to be most effective.