Should i send him to rehab?

my son recently got caught smoking a lot of marijuana. he also took xanax and other prescription drugs such as ritalin and adderall. there are texts on his phone about cocaine. he denies wanting to do more drugs but his school says he comes high everyday and always looks stoned. he is 18. they said to send him to rehab. we have the finances to do so, and i sent him to a drug couselor who is ready to send him next week. he says he has stopped all drugs and i haven't seen him high in a few weeks and he hasn't been out with his friends. however, he drinks all day long. he just had 5 drinks with vodka and cranberry juice in the past hour. what do you suggest?