Long-term administration of large doses of paracetamol impairs the reproductive competence of male rats

Aim: To evaluate the antireproductive effect of paracetamol in male rats. M ethods: Male rats were-orally administered daily with 500 mg/kg or 1000 mg/ kg of paracetamol for 30 consecutive days. Their sexual behaviour and ferti lity were evaluated using receptive females. Results: At 2 h after treratme nt, sexual behaviour was not inhibited but on day 30 both doses of paraceta mol caused marked impairment of Libido (assessed by % mounting, % intromiss ion and % ejaculation), sexual vigour (number of mounts and intromissions a nd copulatory efficiency) or sexual performance (intercopulatory interval). In mating experiments, the fertility (in terms of quantal pregnancy, ferti lity index, implantation index and number of implants) was significantly re duced. All these effects were reversible. The antireproductive effect was n ot due to a general toxicity but due to an increase in pre-implantation los ses resulting from oligozoospermia, impairments of normal and hyper-activat ed sperm motility, and reduction in the fertilizing potential of spermatozo a. Conclusion: Long-term use of high doses of paracetamol may be detrimenta l to male reproductive competence.