Thyrotropin-releasing hormone-induced GH release after cocaine withdrawal in cocaine addicts

During cocaine addiction the hypothalamus-pituitary axis is widely affected and a blunted response of thyroid stimulating hormone (TSH) to thyroid releasing hormone (TRH) consistent with a hyperthyroid state has been observed. Since the thyroid status can affect the release of growth hormone (GH) the authors evaluated TSH and GH responses to TRH in cocaine addicts at the time of drug withdrawal and 30 days after. Twenty-six male cocaine addicts and 11 healthy male control subjects agreed to participate in the study. TRH and placebo tests were performed at random at 5 day intervals at the time of drug withdrawal and after 30 days. In drug addicts, at the time of the first test basal plasma levels of freeT3, freeT4 and TSH were normal, but the TSH response to TRH was impaired. After 30 days of cocaine abstinence basal freeT4 plasma levels were significantly lower, and TSH levels and the TSH response to TRH were higher than in the first test. At the first examination, basal GH concentrations were similar in cocaine addicts and in control subjects and GH did not respond to TRH. After 30 days of abstinence, basal GH plasma levels were unmodified, but the TRH became stimulatory of GH release in cocaine-deprived, but not in control subjects. In conclusion, in cocaine addicts, drug withdrawal is associated with a condition of subclinical hypothyroidism that makes the GH-releasing machinery sensitive to TRH.