What are the long-term effects of using methamphetamines and stimulant type drugs on the thyroid and hypothalamus? After, 25+ years of consistent use and abuse of these drugs, I find that after 5+ years of Being drug free, I cannot lose weight – regardless of the type of healthy diet I follow, exercise regimen or assistance with prescribed medications. I have been diagnosed with hypothyroidism, however, the Synthroid caused me to gain weight and feel awful.