No. The reason we have doctors and pharmacists is to make sure that medications are used safely as determined by the people with sufficient knowledge to make that determination. There are many pain killers that are extremely addictive, and if anything, need MORE restrictions on them. And adults might give or sell some of the drugs (like morphine) to children and teenagers. Certain medications that control mental health problems need to be administered carefully, as taking too much or going cold turkey (as opposed to gradually tapering off of the drug) can cause drastic side effects.
You can also poison people with certain heart medications and other drugs. Yes, you can still do that now if you have a prescription, but because it is given by prescription, the drug can be traced back to you, and to use it as a poison on someone else you would have to deprive yourself of the needed medicine in order to kill that person. There are so many ways to abuse prescription drugs either through ignorance or malevolence that it is a very GOOD thing that we regulate their use.