Introduction: Methylphenidate (MPH) is one of the common medications used for maintaining alertness and improving attention. Monosodium glutamate (MSG) is a food additive, which acts as an enhancer of palatability. The aim of this study was to evaluate the various effects of these compounds on the reproductive system during adolescence.
 
Materials and Methods: Methylphenidate (5 and 10 mg/kg) and monosodium glutamate (6 and 60 mg/kg) were administrated to adolescent rats. After 60 days, the pituitary-testicular axis hormones were assayed and testicular histomorphometric studies were performed.
 
Findings: The coadministration of MPH (5 mg/kg) and MSG (60 mg/kg) led to elevation in serum FSH levels (P<0.05). The highest blood level of luteinizing hormone was observed following high doses of MPH and MSG separately or in combination form. The effect of MPH and MSG on serum testosterone level was observed dose dependently and contradictorily (P>0.05). The administration of MSG led to a reduction in the population of Sertoli cells, spermatogonia, and spermatocyte. Coadministration of MPH and MSG also reduced this population. Morphometric studies revealed decrement of tubular diameter and germinal epithelium height (P<0.05), especially with low doses of MPH and high doses of MSG. The changes in spermatogenic indices were similar to morphometric results. Tubular atrophy, interstitial edema, and depopulation of spermatogenic cells were observed in MPH and MSG treated groups. Coadministration of these compounds increased spermatids with pyknotic nucleus.
 
Conclusion: It has been concluded that the coadministration of MPH and MSG through the induction of some hormonal and structural alterations could induce some changes in the normal structure and function of the reproductive system.