Is it okay to take 100 mg of zoloft?

So my boyfriend has to take zoloft to help him and the doctors gave him 100 mg of it.now before that he was taking 30 mg. after he started to take his medicine when we would have sex.he wouldnt be able to *** like we could have sex for hours and no ***.i personaly dont think he should be taking that much of a dosage.i would like to know if the 100 mg zoloft is okay and safe for his body.btw hes 18 and he weighs around 140