No, it is never ok to take a friend's medication, unless you have been cleared by a doctor
. There are many things that go into prescribing a medication, and it is difficult to know what those are. Some of the factors include allergies, the effectiveness, the effects of the drug on reproduction, and other things. Additionally, if you have not received the proper education prior to taking the drugs, you may not be aware of potential side effects or things to look out for. Many people have serious drug reactions or even die every year because of drug interactions or allergies, and the warning signs are not always obvious. Another problem has to do with the liability you take as the patient: for example, if you are driving after taking many medications (including many muscle relaxers) and get in an accident, it would likely be considered your fault given the impairment that many of these can have on your thinking and ability to react. As you can see, there are many reasons not to take a medication prescribed for someone else. If you are having back pain, please speak with your doctor. That is a common complaint, and there should be something just right for you (and it usually won't start with a muscle relaxer).