Sir.—New drugs usually seem safer than older ones. The vogue for treating thyrotoxicosis with propranolol hydrochloride rather than a thioamide is yet another example of this often unfounded optimism. The article by Newman et al and the commentary by Gardner together provide an excellent summary of the hazards of propranolol therapy in the neonate. I would like to emphasize an additional area of concern: the possibility that propranolol treatment of neonatal toxicosis may have later-emerging developmental consequences. Propranolol is one of a large number of neuroactive drugs whose use is associated with intrauterine growth retardation.1 These reports are cited by Dr Gardner.
We have been studying the effect of oral propranolol on growth and development of suckling rats and find that as little as four days of propranolol administration significantly retards growth in a dose-dependent fashion (unpublished observations). A number of studies have indicated that propranolol can inhibit